Evenings
AT TH E
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Microscope
MF
PH. GOSSE,F. R.S.
%«,. 71 :
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a- 6
EVENINGS AT THE MICROSCOPE ;
OK,
RESEARCHES
AMONG THE MINUTER ORGANS AND FORMS OF
ANIMAL LIFE.
BY
PHILIP HENRY GOSSE, F.R.S.
A NEW EDITION, REVISED AND ANNOTATED.
PUBLISHED UNDEE THE DIRECTION OF THE
COMMITTEE OP GENERAL LITERATURE AND EDUCATION,
APPOINTED BY THE SOCIETY FOE PROMOTING
CHRISTIAN KNOWLEDGE.
LONDON :
SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE ;
NORTHUMBERLAND AVENUE, CHARING CROSS, W.C. ;
43, Queen Yictoeia Street, E.C. ;
26, St. George's Place, Hyde Park Coenee, S.W.
BRIGHTON : 135, Noeth Street.
New York-. E. & J. B. YOUNG & Co.
1884.
7
PREFACE.
-*o*-
To open the path to the myriad wonders of creation,,
which, altogether unseen by the unassisted eye, are
made cognisable to sight by the aid of the micro-
scope, is the aim and scope of this volume. Great
and gorgeous as is the display of Divine power and
wisdom in the things that are seen of all, it may
safely be affirmed that a far more extensive prospect
of these glories lay unheeded and unknown, till the
optician's art revealed it. Like the work of some
mighty genie of Oriental fable, the brazen tube is
the key which unlocks a world of wonder and beauty
before invisible, which one who has once gazed upon
it can never forget, and never cease to admire.
This volume contains but a gleaning : the author
has swept rapidly across the vast field of marvels,
snatching up a gem here and there, and culling one
and another of the brilliant blossoms of this flowery
region, to weave a specimen chaplet, a sample coronal,
which may tell of the good things behind. Yet the
selection has been so made as to leave untouched no
considerable area of the great field of Zoology which
is under the control of the microscope ; so that the
student who shall have verified for himself the obser-
vations here detailed, will be no longer a tyro in
IV EVENINGS AT THE MICROSCOPE.
microscopic science, and will be well prepared to
extendhis independent researches, without any other
limit than that which the finite, though vast, sphere
of study itself presents to him.
The staple of the work now offered to the public
consists of orio-inal observation. The author is far
from thinking lightly of the labours of others in this
ample field ; but still, it is true that, respecting very
many of the subjects that came under his notice, he
found, in endeavouring to reproduce and verify pub-
lished statements, so much perplexity and difficulty
that he was thrown back npon himself and nature,
compelled to observe de novo, and to set down
simply what he himself could see. The ever-
accumulating stock of observed and recorded facts
is the common property of science ; and the author
has not scrupled to reproduce, to amplify, or to
abridge his own observations which have already
appeared in his published works and scientific
memoirs, as freely as he would have cited those of
any other observer in which he had confidence, and
which were germane to his purpose. Yet, in almost
all cases, the observations so used have been sub-
jected to renewed scrutiny, and have been verified
afresh, or corrected where found defective.
In order to relieve as much as possible the dryness
of technical description, a colloquial and familiar style
has been given to the work ; which has been thrown
into the form of a series of imaginary conversaziones,
or microscopical soirees, in which the author is sup-
posed to act as the provider of scientific entertain-
ment and instruction to a circle of friends. It is
proper to add, however, that the precision essential
PREFACE.
to science lias never been consciously sacrificed. A
master may be easy and familiar without being loose
or vague.
A considerable amount of information will be
found incidentally scattered throughout the work on
microscopic manipulation, — the selecting, securing,
and preparing of the objects for examination ; — an
important matter, and one which presents a good
deal of practical difficulty to the beginner. Not a
little help will be afforded to him, also, on the power
to observe and to discriminate what he has under his
eye. In almost every instance, the objects selected
for illustration are common things, such as any one
placed in tolerably favourable circumstances, with
access to sea-shore and country-side, may reasonably
expect to meet with in a twelvemonth/ s round of
research.
The pictorial illustrations are almost co- extensive
with the descriptions ; they are one hundred and
thirteen in number; all, with the exception of
eighteen,* productions of the author's own pencil,
the great majority having been drawn on the wood
direct from the microscope, at the same time as the
respective descriptions were written. He ventures
to hope that they will be found accurate delineations
of the objects represented.
Torquay, February, 1859.
* The subjects on pp. 43, 48, 98, 100, and 151, have been copied,
under the courteous permission of the publisher, from Dr. Carpenter's
valuable work, " The Microscope, and its Kevelations." (Churchill,
London.)
PREFACE TO THE PRESENT EDITION.
In preparing a new edition of this Work for the press,
every page has passed under the Author's eye, and
has been examined with earnest care. A very large
portion of it consisting of his own original re-
searches, there was little room for alteration ; but
new facts, interesting in themselves, and germane to
the subjects herein treated, which have been recorded
since, he has used to enrich the work. These have
been uniformly added in the shape of marginal
notes -, leaving the text untouched, a reflection of
Microscopical Science a quarter of a century ago.
P. H. G.
Torquay, May, 1SS4.
CONTENTS.
CHAPTER I.
Hairs, Feathers, and Scales .
PAGE
CHAPTER II.
Blood .25
CHAPTER III.
Mollusca: their Shells, Tongues, Etes, and Ears . . 3£
CHAPTER IV.
Sea-mats and Shelly Corallines &>
CHAPTER V.
Insects : Wings and their Appendages 70
CHAPTER VI.
Insects : their Breathing Organs 93
CHAPTER VII.
Insects : their Feet 100
CHAPTER VIII.
Insects : their Stings and Ovipositors 125-
CHAPTER IX.
Insects : their Mouths 138.
/ & b~^o
Vlll EVENINGS AT THE MICROSCOPE.
PAGE
CHAPTER X.
Insects : their Ears and Eyes 158
CHAPTER XL
Crabs and Shrimps 171
CHAPTER XII.
Barnacles • 191
CHAPTER XIII.
Spiders and Mites 203
CHAPTER XIV.
Wheel-bearers . 223
CHAPTER XV.
Worms. 258
CHAPTER XVI.
Sea-urchins and Sea-cucumbers 276
CHAPTER XVII.
Jelly-fishes 307
CHAPTER XVIH.
Zoophytes .... 325
CHAPTER XIX.
Sea- Anemones : their Weapons 355
CHAPTER XX.
Protozoa and Sponges 376
CHAPTER XXI
Infusoria 389
LIST OF ILLTJSTKATIONS.
Human Hair
Hog's Bristles
Fibre of Sheep's wool .
Hair of Cat .
Hairs of Mole
Hair of Sable
Hair of Mouse
Tip of Small Hair of Mouse
Hair of Bat .
Hair of Indian Bat
Tip of Hair of Dermestes
Barb of Clothing Feather of
Fowl
Barb from Goose-quill .
Scales of Perch .
Scales of Gold-fish
■Scale of Flounder
Scales of Pike
Spicula of Gold-fish's Scale
Blood-disks
Circulation in Frog's Foot
Perophora .
■Cuttle-shell .
Section of Nacre from Pearl
Oyster
Toogue of Trochus
Structure of Eye of Snail
Leafy Sea-mat
Doubling and Hooks in a
Bee's Wing
Scales on a Gnat's Wing
Bristle-tail .
Scale of Bristle-tail
Page
2
5
7
8
9
9
10
11
II
12
11
15
16
17
19
21
23
21
28
32
33
41
43
48
54
62
74
75
76
^*-
Battledore scale of Polyom
matus Alexis .
Fringed Scale of Pieris
Scales of Diamond-beetle
Air-pipe of Fly .
Spiracle of Fly
Spiracle of Leather-coat
Spiracle of Cockchafer-grub
Grub of Chameleon-fly
Foot of Fly .
Foot of Water-beetle .
Sting of Bee
Gall-fly, and Mechanism of
Ovipositor
Outer Saw of Saw-fly .
Inner Saw of Saw-fly .
Mouth of Beetle .
Jaws of Bee
Lancets of Female Gnat
Tongue of Blow-fly
Sucker of Butterfly
Antenna of Cockchafer
Antenna of Oak Egger Moth
Ear of Crab .
Daphnia
Cypris ....
Zoea of Shore-crab
Second Stage of Shore-crab
Third Stage of Shore- crab
Adult Shore-crab
Hand of Barnacle
Young of Barnacle
Fang of Spider . ,
Page
80
81
83
95
98
99
100
102
116
118
127
128
133
134
140
142
150
151
156
162
164
172
179
181
183
185
187
188
193
197
206
EVENINGS AT THE MICROSCOPE.
Eyes of Spider
Claws of Spider .
Head of Cheese-mite .
Page
207
217
221
Cydippe ....
Sarsia .....
Thaumantias
Page
310
316
319
Brachionus .
232
Otolithes of Thaumantias .
320
Mouth of Brachionus .
235
Turris and its Young .
324
Whiptail
239
Laomedea ....
328
Skeleton Wheel-bearer
243
Tentacle of Laomedea
329
Sword-bearer
247
Stauridia ....
342
Tripod Wheel-bearer .
Two-lipped Tube-Wheel
Wheels of Tube-wheel
Foot of Nais
249
252
253
. 262
Lares .....
Polypes of Cow's Pap .
Spicula of Cow's Pap .
Portion of Acontium .
345
351
353
357
Throat of Leech Laid Open
Jaw of Leech
Pushing Poles of Serpula
Hooks of Serpula
Spine of Echinus .
. 269
. 270
. 273
274
281
Cinclides ....
Cnida of Madrepore .
Cnida of Tealia .
Cnida of Corynactis
Forms of Amoeba
358
364
367
370
379
Head of Pedicellaria Triden
3 284
Section of Sponge
386
Sucker of Urchin
289
Three-sided Euglena .
391
Pores of Urchin .
289
Swan-neck and its Divisions
394
Sucker-plate of Urchin
292
Paramcecium
398
Dumb-bells in Holothuria
298
Ccleps and Chilomonas
399
Wheel in Chirodota .
298
Vorticellse ....
402
Anchor-plate in Synapta
Larva of Sea-urchin
299
303
Acineta ....
Vaginicola ....
407
410
Young Sea-urchin: Deve
lopment of Disk
305
Euplotes ....
416
EVENINGS
AT THE MICROSCOPE.
-»<>♦-
CHAPTER I.
IIAIIJS, FEATHERS, AND SCALES.
Kot many years ago an eminent microscopist received a
communication inquiring whether, if a minute portion of
dried skin were submitted to him, he could determine it
to be human skin or not. He replied that he thought
he could. Accordingly a very minute fragment was
forwarded to him, somewhat resembling what might be
torn from the surface of an old trunk, with all the hair
rubbed off.
The professor brought his microscope to bear upon it,
and presently found some fine hairs scattered over the
surface ; which, after carefully examining them, he
pronounced with confidence to be human hairs, and
such as grew on the naked parts of the body ; and
declared the person who had owned them to have been
of a fair complexion.
This was a very interesting decision, because the frag-
ment of skin was taken from the door of an old church
in Yorkshire ;* in the vicinity of which a tradition is
* I am writing from memory, having no means of referring- to the
original record, which will be found in the first (or second) volume of
the "Transactions of the Microscopical Society " of London. The
general facts, however, may be depended on.
B
EVENINGS AT THE MICROSCOPE.
preserved, that, about a thousand years ago, a Danish
robber had violated this church, and, having been taken,
had been condemned to be flayed, and his skin nailed to
the church-door, as a terror to evil-doers. The action of
the weather and other causes had long ago removed all
traces of the stretched and dried skin, except that, from
under the edges of the broad-headed nails with which
the door was studded, fragments still peeped out. It
was one of those atoms, obtained by drawing one of the
old nails, that was now subjected to microscopical scru-
tiny ; and it was interesting to find that the wonder-
showing tube could confirm the tradition with the utmost
certainty ; not only in the general fact, that it was really
the skin of man, but in the special fact of the race to
which that man belonged, viz., one with fair complexion and
light hair, such as the Danes are well known to possess.
It is evident from this anecdote that the human hair
presents characters which are so indelible that centuries
of exposure do not avail to obliterate them,
and which readily distinguish it from the hair
of any other creature. Let us then begin our
evening's entertainment by an examination of
a human hair, and a comparison of it with
that which belongs to various animals.
Here, then, is a hair from my own head. I
cut oft" about half-an-inch of its length, and,
laying it between two plates of glass, put it
upon the stage of the microscope. I now
apply a power of 600 diameters ; that is, the
apparent increase of thickness is the same as
if six hundred of these hairs were placed side
by side. Now, with this eye-piece micrometer,
we will first of all measure its diameter.
You see, crossing the bright circular field
of view, a semi-pellucid cylindrical object •
that is the hair. You see also a number of fine
HVMAN HAIR.
HAIRS, FEATHERS, AND SCALPS. 6
lines drawn parallel to each other, exactly like those on
an ivory rule or scale, with every fifth line longer than the
rest, and every tenth longer still. This is the micrometer,
or scale by which we measure objects; and the difference
in the length of the lines, you will readily guess, is merely
a device to facilitate the counting of them. By moving
the stage up or down, or to either side, we easily bring
the hair exactly into the centre of the field ; and now,
by adjusting the eye-piece, we make the scale to lie
directly across the hair, at right angles with its length.
Thus we see that its diameter covers just thirty of the
fine lines ; and as, with this magnifying power, each
line represents 1-1 0,000th of an inch, the hair is 30-
10,000ths, = —^1x1 of an inch, in diameter.
In all branches of natural history, but perhaps pre-
eminently in microscopic natural history, — owing to its
greater liability to error from deceptive appearances, — we
gain much information on any given structure by com-
paring it with parallel or analogous structures in other
forms. Thus we shall find that our understanding of the
structure of this hair will be much increased when we have
seen, under the same magnifying power, specimens of the
hair of other animals. In order, however, to explain it, I
must anticipate those observations.
What Ave see, then, is a perfectly translucent cylinder,
having a light brown tinge, and marked with a great
number of delicate lines, having a general transverse
direction, but very irregularly sinuous or winding in
their individual courses. These lines we perceive to be
on the surface ; because, if we slowly turn the adjustment-
screw, the lines grow dim on the central part of the
cylinder, while those parts that lie near the edges (speak-
ing according to the optical appearance) come into dis-
tinctness. Presently the edges of the cylinder become
sharply defined, and are seen to be cut into exceedingly
shallow saw-like teeth, about as far apart as the lines ;
b 2
4 EVENINGS AT THE MICROSCOPE.
these, however, are so slight that they can be seen only
by very delicate adjustment. We go on turning the
screw, and presently another series of transverse lines,
having the same characters as the former, but differing
from them individually, come into view, at the sides first,
and presently in the middie, and then, as we still turn,
become dim, and the whole is confused. In fact, our eye
has travelled, in this process, from the nearer surface of
the hair, right through its transparent substance, to the
farther surface : and we have seen that it is surrounded
by these sinuous lines, which the edges — or those portions
of the hair which would be the edges, if it were split
through the middle (for, optically, this is the same thing)
— show to be successive coats of the surface, suddenlv
terminated. If we suppose a cylinder to be formed of very
thin paper, rolled up, and then, by means of a turning-
lathe, this cylinder to be tapered into a very lengthened
cone, the whole would be surrounded by lines marking the
cut-through edges of the successive layers of paper ; and,
owing to the thickness of the paper not being mathema-
tically equal in every part, these edges would be sinuous ;
exactly as we see in these lines upon the hair. The
effect and the cause are the same in the two cases.
A hair is closely analogous to the stem of a plant :
inasmuch as it grows from a root, by continual additions
of cells to the lower parts, which, as they lengthen, push
forward the ever-extending tip. Indeed, in some of the
hairs which we shall presently look at, there is the most
curious resemblance to the stem of a palm, with the
projections produced by the successive growth and break-
ing away of leaf-bases around the central cylinder. In-
ternally, too, the resemblance is remarkable ; for, if we
split a human hair, and especially if we macerate it, i.e.
soften it by soaking it, in weak muriatic acid, we shall
find it composed of (1) a thin but dense kind of bark,
forming the successive overlapping scales just described :.
HAIRS, FEATHERS, AND SCALES.
{2) a fibrous substance, extending from the bulb to the
point of the hair. By soaking the hair in hot sulphuric
•acid, this fibrous substance resolves itself into an immense
number of very long cells, pointed at each end, and
squeezed by mutual pressure into various angular forms.
" A human hair, of one-tenth of a line in thickness,* has
about 250 fibrils in its mere diameter, and about 50,000
in its entire calibre : so that these ultimate fibrils are
finer than those of almost any other known tissue, from
the great elongation and narrowing of their constituent
cells as they are drawn out into the shaft of the hair
during growth : and hence the expanded bulb of the hair,
where the cells are yet spherical and soft."f (3) Running
through the very centre of the fibrous portion may be
sometimes discerned a dark slender line, which is a sort of
pith (medulla) composed of minute roundish cells, filled
Avith air, and arranged in two or three rows. J
HOG S HRISTLE*.
The bristles of the Hog bear much resemblance to the
human hair. On this slide is one (a), which you perceive
* This is nearly thrice as great as the diameter I have given above,
which i.s the result of several careful admeasurements of diffeient
hairs, taken from childhood and adult age.
f Grant, "Outl. Comp. Anat.," 647.
£ " The cortical (or bark-like) substance has different colour, accord-
ing to the colour of the hair ; generally, the colour is diffused through
its whole mass ; less frequently, the colour depends on granular pigment
scattered through its substance in small masses. The cortical substance
6 EVENINGS AT THE MICROSCOPE.
is just thrice as thick as the hair that we have been
examining, or y^^th of an inch in diameter. The sinuous
lines across the surface are proportionally far finer and
closer together, and no saw-teeth are visible at the edge,
the most delicate adjustment showing only a minute un-
dulation in the outline ; that is to say, the overlapping
scales are far thinner, and therefore their terminations are
nearer together, in the hair of the Swine than in that of
Man. I will now show you a transverse section of a similar
bristle, which I will obtain thus : I take this old brush,
and with a razor cut off one of the bundles of bristles,
close to the wood ; then I take off as thin a shaving as
I can cut, wood, bristles, and all ; I repeat the same opera-
tion two or three times. Now, having picked out the
shavings of wood, I take up with the point of my pen-
knife a few of the dust-like atoms that remain, and scatter
them on this plate (or slide) of glass, and these I cover
with another plate of thin glass; for this dust is composed
of thin transverse slices of the bristles, and as I scatter
contains a number of cavities filled with air, most evident in the hair
from aged persons, or in dry hair.
" The central portion, the medulla, forms, when well developed, an
axis-cylinder, one-fifth, or one-fourth, the diameter of the hair, with
sharp outlines, generally central, but often a little excentric in position.
It is often wanting in human hair, especially in blond hair. ... In
woolly hair it is always wanting ; also in the hair of the new-born
child. The medullary substance is often interrupted, and sometimes
consists of only a few dark points lying in the axis of the hair . .
The medullary substance has been thought to contain the pigment : this
is not so, the supposed pigment granules being very minute air- bubbles.
The cause of the colour of the hair is found in the diffuse pigmentation
of the cortical substance. The cause for the hair becoming grey or
white is to be found in the disappearance of the diffuse pigmentation
of the cortical substance, the cause of which is not yet known. The
medullary substance can be more easily seen in white hair than in
coloured." (From a valuable memoir, entitled, " Hair in its Micro-
scopical and Medico-legal Aspects," by Dr. E. Hofman ; transferred to
the "English Mechanic" for May 9, 18/3, from the " Xew York
Medical Journal.")
HAIRS, FEATHERS, AND SCALES.
them, some will fall upon their cut ends, so that we shall
look through them endwise.
Here is one, very suitable for examination (b), — since it
is not a whole section, the razor having passed somewhat
obliquely across it, coming out beyond the middle, where
it thins away to an edge. The outline is not circular,
but elliptical; that is, the hair is not round, but flattened.
There is no separable cortex, or bark, and the whole sub-
stance appears as if made up of exceedingly fine fibres, of
which we see the ends cut across. A rough dark line
occupies the middle of the slice, in the plane of the
greater diameter ; but at the edge of the slice we are able
to see that this is not a solid core, as has been sometimes
supposed, but a cavity passing up through the hair. It is
surrounded by a layer of cells, called medullary, and
which appear black, because they are filled with air.
The finer hairs of the Horse and the Ass,
such as those selected from the cheeks, have
the sinuous edges of the plates about as
close as in human hair. But they are dis-
tinguished at once by the conspicuousness of
the medullary portion, which is thick, and
quite opaque, and is broken up (especially
towards each extremity of the hair) into
separate longitudinal irregular masses.
The fine wool of the Sheep is clothed with
imbrications, * proportionally much fewer than
those of human hair, while the diameter is
also much less. Thus these examples, selected
from fine flannel and from coarse worsted,
vary in diameter from ^^th to T£ -^th of an
inch ; and there are, upon an average, about
two imbrications in a space equal to the dia-
meter. No colour is perceptible in these spe- SHFKP'S woot"
FIBRE OF
* A structure is said to be imbricated when it is arranged like tiles
on the roof of a house.
8
EVENINGS AT THE MICROSCOPE.
cimens ; they are as transparent and colourless as glass.
The imbricated plates project here considerably more
than in either of the examples we before examined ;
the " teeth," however, form an obtuse angle.
We shall presently see the importance of this imbri-
cate structure ; but we will first look at a few more
examples, in which we shall find it still more strongly
developed, in conjunction with some other peculiarities.
All the hairs that we have looked at are what I have
called fibrous in their interior texture, but those of
many animals are more distinctly cellular.
Thus, in these specimens, plucked from the fur of the
Cat that lies coiled up on the hearthrug, we see, first, that
the imbrications are short, being about equal
to thediameterinlength,but are very strongly
marked ; though, like those of the Sheep's
wool, obtuse. Hence the outline is extremely
like that of the stem of an old rough palm-
tree. There is a distinct bark (cortex), which
is thick, and marked with longitudinal lines,
which add to the resemblance just alluded to.
The interior is clear, marked off at pretty
regular intervals by the broad flattened me-
dullary cells, in single series, each cell occu-
pying, for the most part, the whole breadth
of the interior. These cells are transparent,
and apparently empty ; but their walls ap-
pear opaque and almost black, — an optical
illusion, dependent on the absorption of the
light by their surfaces at certain angles with
the eye of the beholder. The fibrous portion is here
almost displaced by the great development of the medul-
lary cells.
In the larger hairs of the Mole, which we will now look
at, the bark is very thin ; and though the surface is
marked with sinuous lines, these do not project into teeth.
iE!
HAIR OF CAT.
HAIRS, FEATHERS, AND SCALES.
HAIRS OF MOLE.
The pith here again forms the greater portion of the hair,
the cells of which it is composed being placed in single
series, which, for the most part,
extend all across the body of
the hair, though they are some-
what irregular both in size
and shape. They are rather
flattened, and appear per-
fectly black (that is, opaque)
by transmitted light, their sur-
faces absorbing all the rays of
light. The small hairs of the
same animal, however, are very
different in form : they are
flattened, so as to appear twice
as broad in one aspect as in
another at right angles to it ;
and, what is curious, the
scales of the bark project into strongly-marked imbrica-
tions on one side, and are scarcely perceptible on the
other. Here, as in the larger hairs, there is a single row
of oval transverse cells, perfectly opaque.
The hair of many of the !ta
smaller Mammalia shows
considerable diversity of
form, according to the part
which we select for obser-
vation. Thus, if we take
a long hair out of this
Sable tippet, and examine
it near the base, we sec
(a) that it is very slender,
transparent, and color, r-
less, covered with strongly
marked imbrications, which
are not obtuse teeth, but
HAIR OF SABLE.
10
EVENINGS AT THE MICROSCOPE.
long, pointed, overlapping scales, about ten of which
form a complete ring, or whorl, as it is called. The
fibrous portion is moderately thick ; inclosing a wide
pith of roundish cells, set in two rows, that allow the
rays of light to be transmitted through their central
parts.
As we trace the hair upwards (b), by moving the
stage of the microscope, by-and-by it swells and
rapidly increases in thickness ; the imbrications are
scarcely perceptible ; while the pith-cells have greatly
augmented in number and in breadth. These are ar-
ranged in confused close set, transverse rows, and are
nearly opaque.
Still tracing up the same hair, as we approach the tip,
the bark and fibrous part become very thin ; the cells are
fewer and fewer till thev cease altogether, and a lom>-
slender point, of a clear yellow tinge, without cells, pre-
sents tranverse wavy lines of imbrication scarcely pro-
iecting,
The hair of the common Alouse is a pretty and inter-
esting object. In the larger speci-
mens the fibrous portion is reduced
almost to nothing. The imbrica-
tions project very little, but care-
ful observation reveals slanting;
lines proceeding from the "teeth;"
which show that the whole surface
is clothed with large pointed scales,
which are very thin, and lie close.
The pith consists of large flattened
cells, arranged thus : one row
passes up through the centre, and
other similar ones are set in a
circle around it, so that a longitudi-
nal section would show threeparal-
These cells are translucent, and some of them
HAIR OF MOUSE.
lei rows.
HAIRS, FEATHERS. AND SCALES. 11
are either wholly or partially lined with a clear yellow
pigment, or colouring- matter.
The smaller hairs from the same little animal
are scarcely distinguishable from those of the Cat,
already described, except that the imbrications are
proportionally larger. In all, the extremity is
drawn out to a lengthened fine point, and is occu-
pied with clear yellow cells, except the very tip,
which is colourless, and imbricated with sinuous
whorls, each consisting of a single scale.
But it is in the Bats that the imbricated
character attains its greatest development.
On this slide is a number of hairs from the
fur of one of our English Bats, in which it is
far more conspicuous than in any example
we have yet seen. In the middle portion of
each hair the scales lie close, embracing their
successors to the very edges, or nearly : but
the lower part, which is more slender, re-
sembles a multitude of trumpet-shaped flowers
formed into a chain, each being inserted into
the throat of another. The lip of the "flower''
is generally oblique, and here and there we
can perceive that each is formed of two half-
encircling scales ; for one scale occasionally
mouse, springs from the level of its fellow, so as to 0"Abat.
make the imbrication alternate.
Even this, however, is far excelled by a species of Bat
from India, of whose hair I have now specimens on the
stage. The trumpet-like cups are here very thin and
transparent, but very expansive ; the diameter of the lip
being, in some parts of the hair, fully thrice as great as
that of the stem itself. The margin of each cup appears
to be undivided, but very irregularly notched and cut.
In the middle portion of the hair, the cups are far more
crowded than in the basal part, more brush-like, and less
TIP OP
SMALL
HAIB
OP
12
EVENINGS AT THE MICROSCOPE.
elegant ; and this structure is continued to the very ex-
tremity, which is not drawn out to so attenuated a point
as the hair of the Mouse, though it is of a needle-like
sharpness. The trumpet-shaped scales
are, it seems, liable to be removed by
i Ws"jL II accident; for in these dozen hairs there
V"'-K are several in which we see one or more
H/ cups rubbed off, and in one the stem is
destitute of them for a considerable
space. The stem so denuded closely
resembles the basal part of a Mouse's
hair in its ordinary condition.
This character of being clothed witli
overlapping scales, each growing out of
its predecessor, is common, then, to the
hairs of the Mammalia, though it exists
in different degrees of development. It
may be readily detected by the unaided
sense, even when the eye, though as-
sisted by the microscope, fails to recog-
nise it. Almost every schoolboy is familiar with the mode
by which the tip of any hair may be distinguished from
its base ; and, even of the least fragment, the terminal end
from the basal end. A hair is rubbed to and fro between
the finger and thumb, and it regularly travels through in
the direction of its base ; thus enabling the boy after one
or two rubs to pronounce a very decided opinion on the
subject. Now you see the cause of this property lies in
the imbricate structure ; the scales may be ever so thin
and close, but still they project sufficiently in any speci-
men to present a barrier to motion in the direction of
the tip when pressed between two surfaces, such as the
fingers, while they very readily move in the oppc site.
But more than the success of a schoolboy's magic de-
pends on the imbricate surface of hairs. England's time-
honoured manufacture, that which affords the highest
HAIR OF INDIAN BAT.
HAIRS, FEATHERS, AND SCALES. 1 -°>
seat in her most august assembly, depends on it. The
hat on your head, the coat on your back, the flannel
waistcoat that shields your chest, the double hose that
comfort your ankles, the carpet under your feet, and
hundreds of other necessaries of life, are what they are,
because mammalian hairs are covered with sheathing
scales.
It is owin£ to this structure that those hairs which
possess it in an appreciable degree are endowed with the
property of felting ; that is, of being, especially under the
combined action of heat, moisture, motion, and pressure,
so interlaced and entangled as to become inseparable; and
of gradually forming a dense and cloth-like texture. The
" body " or substance of the best sort of men's hats is
made of lamb's wool and rabbit's fur, not interwoven, but
simply beaten, pressed, and worked together, between
damp cloths. The same property enables woven woollen
tissues to become close and thick ; every one knows that
worsted stockings shrink in their dimensions, but become
much thicker and firmer, after they have been worn and
washed a little ; and the " stout broad-cloth," which has
been the characteristic covering of Englishmen for ages,
would be but a poor, open, flimsy texture, but for the
intimate union of the felted wool fibres, which accrues
from the various processes to which the fabric has been
subjected.
In a commercial view, the excellence of wool is tested
by the closeness of its imbrications. When first the wool-
fibre was submitted to microscopical examination, the ex-
periment was made on a specimen of Merino; it presented
2,400 little teeth in an inch. Then a fibre of Saxon wool,
finer than the former, and known to possess a superior
felting power, was tried: there were 2,720 teeth in an
inch. Next a specimen of South-Down wool, acknow-
ledged to be inferior to either of the former, was
examined, and gave 2,080 teeth. Finally, the Leicester
14
EVENINGS AT THE MICROSCOFE.
wool, whose felting property is feebler still, yielded only
1,850 teeth per inch. And this connection of good
felting quality with the number and sharpness of the
sheathing scales, is found to be invariable.
The hairs of many insects are curious and interesting.
Here you may see the head of the hive bee, which is
moderately clothed with hair ; each hair is slender and
pointed, and is beset with a multitude of other short
hairs, which project from the main stem, and stand out
at an angle : these are set on in a spiral order. Here,
again, is one of the hinder legs of the same bee : the
yellow hair, which you can see with the naked eye, con-
sists of strong, horny, curved spines, each of which is
scored obliquely, like a butcher's steel. These legs are
used, as you are well aware, to brush off the pollen from
the anthers of flowers, wherewith the substance called bee-
bread, the food of the grubs, is made : and in
this specimen, you may see hundreds of the
beautiful oval pollen-grains entangled among
these formidable-looking spines.
These rusty hairs are from a large cater-
pillar (that of the Oak Egger Moth, I believe) ;
they appear, when highly magnified, like stout
horny rods drawn out to a sharp point, and
sending forth alternate short pointed spines,
which scarcely project from the line of the
axis.
But there is scarcely any hair more curious
than that of a troublesome grub in museums
and cabinets, the larva of Dermestes lardarius,
which lives upon fur-skins, and any dried
animal substances. It has a cylindrical shaft,
which is covered with whorls of large close-set
spines, four or five in each whorl, closely succeeding each
other; the upper part of the shaft is surrounded by a whorl
of larger and more knotted spines, and the extremity
TIP OF HAIR OF
DEBMESTES.
HAIRS, FEATHERS, AND SCALES.
15
is furnished with six or seven large filaments or threads,
which appear to have a knob-like hinge in the middle, by
which they are bent up on themselves.
The feathers of Birds are essentially hairs. That
shrivelled membrane which we pull out of the interior of a
quill when we make a pen, is the medullary portion, dried.
There is a beautiful contrivance in the barbs, or beards, of
most feathers, which I will illustrate by this feather from
the body-plumage of the domestic
fowl. Every one must have ob-
served the regular arrangement of
the vane of a feather, and the ex-
quisite manner in which the beards
of which it is composed are con-
nected together. This is espe-
cially observable in the wing-fea-
thers— a goose-quill for example, L^.
where the vane, though very light j
and thin, forms an exceedingly
firm resisting medium, the indi-
vidual beards maintaining their
union with great tenacity, and re-
suming it immediately, when they
have been violently separated.
]N~ow this property is of high
importance in the economy of the EAEB 0F ™;™LG FE^THEE
bird. It is essential that with
great lightness and buoyancy — for the bird is a flying
creature — there be power to strike the air with a broad
resisting surface. The wide vanes of the quill-feathers
afford these two requisites, strength and lightness ; the
latter depending on the material employed, which is very
cellular, and the former on the mode in which the indi-
vidual barbs, set edgewise to the direction of the stroke,
take a firm hold on each other.
jSTow, in the bodv-feather, which is under the micro-
16
EVENINGS AT THE MICROSCOPE.
scope, we see that the central stem carries on each side a
row of barbs, which interlock with each other. The mag-
nifying power shows us that these barbs are not simple
filaments, but are themselves doubly bearded in the same
fashion ; and further, that these little beards, called bar-
bules, of the second series, are furnished with a third
series. It is in this third series of filaments, called bar-
bulets, that the tenacity in question resides. If we isolate
one of the primary beards, by stripping away a few on
each side of it, and again put it on the stage, we see that
the secondary barbules of one side are armed differently
from those of the other side. Those of the lower side
carry short and simple barbulets, whereas those of the side
which looks towards the point of the feather bear much
longer ones ; and, moreover, many of them are abruptly
hooked backwards. Xow, whenever the primary beards
are brought into contact, some of these hooks catch on
the barbule next above, and, slipping into the angles
formed by the barbulets, hold there, and thus the two
contiguous beards are firmly locked together.
In the beard of the goose-quill,
the structure is essentially the
same, but the barbulets are far
more numerous and more closely
set ; they are also proportionally
much larger — both those which
are hooked and those which are
simple. Indeed, the latter mani-
fest a tendency to the hooked
form, and by all these peculiari-
ties the interlocking power is aug-
mented. It is interesting to ob-
serve the great expansion of the
beard in a direction towards the
interior surface of the feather —
barb fbom GoosB-QiiLL. towards the stroke, as I just now
HAIRS, FEATHERS, AND SCALES.
17
observed. This is to increase the resisting power, as a
thin board set edgewise will bear a great weight without
bending or breaking, provided it can be kept from
yielding sidewise. The barbules are arranged only on
the very edge, the upper edge, of the beard.
We will now examine some specimens of scales of
Fishes, all of which are very interesting and beautiful
objects, under low powers of the microscope ; though
higher powers are requisite to resolve their structure.
We will use both.
The scales of almost all the Fishes with which we are
familiar, fall under two kinds, which have been named
-ctenoid (or comb-like), and cycloid (or roundish). The
</
SCALES OF PEBLH.
Perch affords us good examples of the former kind. On
this slide are three scales from the body of this fish : the
one on the left side is taken from the back (a) : the
middle one from the lateral line (b) ; and the one on the
right from the belly (c). In order to understand these
objects, we must remember that the scales of Fishes are
horny or bony plates, developed in the substance of the
proper skin, with a layer of which they are always covered.
In most cases (as, for example, the Perch), the hinder end
of each scale projects, carrying with it the thin layer of
.skin with which it is invested ; and thus the scales overlav
one another, like the tiles of a house, or like the feathers
of a bird, and that for a like purpose. For as the rain,
c
IS EVENINGS AT THE MICROSCOPE.
falling on the housetop, has a tendency to flow down-
wards, from gravitation ; and as the slope of the roof is
in that direction, the current passing over each tile is
deposited from its bottom-edge on the middle of the
next, whence it still flows down to the free edge, —
and so in succession. So the motion of the bird through
the air, and of the fish through the water, produces the
very same effect as if these fluids were in motion, and the
animals were still ; and therefore the bodies of the latter
are, as it were, tiled with feathers or scales, the free edges
of which, looking in the opposite direction to the coming
of the current (that is, the same direction as its flow),
deposit the successive particles of the moving fluid in
the midst of the successive feathers or scales. Thus two
results ensue, both essential to the comfort of the animal :
first, the air or water does not run upward between the
feathers or scales to the skin ; and secondly, the surface
presents no impediment to free motion. This latter
advantage will be appreciated, if you take hold of a dead
bird by the legs, and push it rapidly through the air
tail foremost : the feathers will instantly rise and ruffle
up, presenting a powerful resistance to movement in
that direction.
These scales of the Perch have their hinder, or free
edge, set with fine crystalline points, arranged in succes-
sive rows, and overlapping, Their front side is cut with
a scolloped pattern, the extremities of undulations of the
surface that radiate from a common point behind the
centre. These undulations are separated by narrow fur-
rows, across which, contrary to the ordinary rule, the
close-set lines that follow the sinuosities of the outline
are not visible. Under the microscope they look as if they
had been split in these radiating lines, after the whole
number of layers had been completed, and the fissures
had then been filled with new transparent substance.
The middle scale is, as I have said, from the lateral
HAIRS, FEATHERS, AND SCALES.
19
line. Along each side, in most fishes, may be observed a
line, known as the lateral line, formed by scales of pecu-
liar form. They are commonly more bony than the
other scales, and are pierced by a tubular orifioe for the
escape (as is generally supposed, though this has been
denied) of a mucous secretion, which is poured out from
glands beneath, and thus Hows over the body for the
double purpose of protecting the skin from the mace-
rating influence of the surrounding water, and of
diminishing friction in swimming.
Let us now look at some scales of the cycloid kind.
The great majority of our fishes are clothed with such
as are of this description. This dead Gold-fish shall give
us examples. The three scales in the upper row are from
SCALES OF GOLD-FISH.
the lateral line, the left-hand one (a) taken just behind
the head, the second (b) near the middle of the body, and
the right-hand one (c) near the tail. Of the lower row, the
first (d) is from the back, the second (?) from the middle
c 2
20 EVENINGS AT THE MICROSCOPE.
of the belly, and the last (f) from the throat. Thus we
see there is considerable variety in form presented by the
scales even of the same individual fish. They all, how-
ever, differ from those of the Perch, in this respect ; — that
their free overlapping edges are entire, or destitute of the
crystalline points which we saw in the former examples ;
while they agree in having the front edges, by which they
are during life imbedded in the skin, cut into waves or
sinuosities. The lower part, as we now look at them, is
the free portion of each, which alone is visible in the living
fish, the other parts being concealed by the three neigh-
bouring scales that overlap it, — above, in front, and below.
In those from the lateral line, the tube already referred
to is seen to pervade each, running through it longitudi-
nally, so that it opens behind on the outer surface, and
in front on the inner or under surface of the scale. In
the scales near the front of the line, just behind the
head, the tube is large and prominent (a), while in the
scales at the opposite extremity it becomes slender ;
diminishing, in the very last scale, viz., at the commence-
ment of the tail-fin, to a mere groove.
The whole surface of each scale, when viewed under a
lens of low power, is seen to be covered with concentric-
lines, following the irregular sinuosities of the outline.
These lines are the edges of the successive layers of which
the scale is believed to be composed, each layer being
added in the process of growth to the under surface, and
each being a little larger every way than its predecessor;
thus the scale is a very depressed cone, of which the centre
is the apex. There is a marked difference (indicated in
the figures) between that part of the surface which is ex-
posed, and that which is covered by the other scales : the
concentric marks in the former are much coarser and less
regular, often being interrupted, and seeming to run into
each other, and frequently swelling into oval scars. This
may, perhaps, be owing to the surface having been par-
IIAIUS, FEATHERS, AND SCALES.
21
tially worn down by rubbing against the gravel of the
bottom, or against other objects in the water. Besides
the concentric lines, there are seen on many of the scales,
especially those of the lateral line, radiating lines varying
in number from one to twenty, or more, diverging from
the centre towards the circumference, and frequently
connected by cross lines forming a sort of net-work
around the centre (see c). Under the microscope, these
lines appear to be elevated ridges, dividing the con-
i fiitric lines ; but of their use I am ignorant.
What I have just stated is the ordinary explanation of
these hoe concentric lines ; but a careful examination of
the structure with much higher powers than we have been
using, induces me to doubt its correctness. Reverting to
the scales of the Perch,
let us notice the clear
diverging bands, which
look as if the whole scale
had been split in several
places, and the openings
thus made filled with
uniform clear substance.
The same structure is
seen in many other
scales, as in this cycloid
one from the Flounder
which, beinof coarse! v lined, shows the structure well; or
i n these from the Green Wrasse. I will now apply to one
of these a power of 600 diameters, concentrating the light
thrown through the scale from the mirror by the achromatic-
condenser,* and examine the scale anew. You now see
two distinct layers : the upper one which bears the con-
centric lines, and a lower clear one which not only fills the
' Called achromatic, from its being so constructed as not to split the
li'dit coming through it and cause colour. The term is tunned from
the Creek a, k<>L Yptoua (chroma), colour.
SCALE OF FLOUNDER.
a. Natural size.
'22 EVENINGS AT THE MICROSCOPE.
radiating bands, but underlies the whole of the lined
parts. The concentric lines of the upper layer do not
now appear to be edges of successive plates, but irregular
canals running through the solid substance. This, how-
ever, is deceptive : for, by delicate focussing, we perceive
that each portion marked by these lines is really in a
different plane from the others, that the highest is at the
centre of radiation of the scale, and that each is succes-
sively lower till we reach the margin. But now, if with
very sharp scissors we cut one of these scales longitudi-
nally through the centre, and examine the cut edge, we
find that each of these lines forms a distinct ridge. On
the other hand, the under layer of clear substance is quite
smooth, and always a little exceeds the margin of the
concentrically lined portion. The clear substance that
tills the radiating slits agrees both in texture and level with
this lower layer, and is manifestly continuous with it.
Hence, I think that, in these slit scales, the upper layer
is formed, as commonly believed, by successive deposits
from beneath ; but that, after a few have been deposited,
they begin to slit, probably by contraction in becoming
solid ; that the lower layer is formed after each upper one
is hardened, exceeding its length by a little, and filling
up the slit ; that this lower layer becomes the upper
layer of the next course, slitting, and turning up its
terminal edge as it hardens ; that then the lower layer
is deposited on this, filling up the slit as before ; and
that this process goes on as long as the fish lives.
It is curious that, in the scales of the Pike, the por-
tions thus separated by slitting, instead of expanding
and leaving spaces to be filled up, actually close over
each other, the divided parts overlapping considerably,
as you may see in these specimens. The left-hand scale
(a) is from the back ; the central one (6), which has only a
deep narrow incision instead of a tube, is from the lateral
line ; and the third (c) is from the belly of the fish.
HAIRS, FEATHERS, AND SCALES.
23
Let us return now to the scales of our Gold-fish, and
examine a highly interesting structure connected with
them. The brilliant golden or silvery reflection that con-
stitutes the beauty of these lovely fishes, depends not on
the scales themselves, but on a soft layer of pigment spread
over their inner surface, and seen through theirtranslucent
substance. On carefully detaching a scale, we see on the
under side, opposite to that portion only which was ex-
posed (all the concealed parts being colourless), a layer of
soft gleaming substance, easily separable, either silvery or
golden, according to the hue of the fish. If now we remove
a small portion of this substance with a fine needle, and
(i
SCALES OF PIKE.
spread it on a plate of thin glass, we shall find, by the aid
of the microscope, that it consists of two distinct sub-
stances ; the one giving the colour, the other the metallic
lustre. Witha power of 300 diameters, the former is seen
to be a layer of loose membranous cells, of an orange
colour in what are properly called the Gold-fishes, and
whitish or pellucid in the Silver-fishes. If we now add a
minute drop of water to the mass, and gently agitate it
with the point of a needle, and again submit it to the
microscope, we shall have a beautiful and interesting spec-
tacle. The water around the mass is seen to be full of an
infinite number of flat spicula or crystals, varying much
in size, but of very constant form, a flat oblong prism
2-t EVENINGS AT THE MICROSCOPE.
with angular ends (as represented in the accompanying
engraving). By transmitted light they are so transparent
and filmy as to be only just discernible ;
but by reflected light, and especially
under the sun's rays, thev flash like
plates of polished steel. But what ap-
pears most singular, is that each spicu-
lum is perpetually vibrating and quiver-
ing with a motion apparently quite spon-
taneous, but probably to be referred to
slight vibrations of the water in which
spicula of gold-fish's they float \ and each independently of
SCALES. i i 1 •
the rest, so as to convey the impres-
sion to the observer that each is animated with life, though
the scale be taken from a lish some days dead. Owing to
this irregular motion, and consequent change of position,
each spiculum, as it assumes or leaves the reflecting angle,
is momentarily brightening or waning, flashing out or
retiring into darkness, producing a magic effect on the
admiring observer. To this property, I suppose, is to be
attributed the beautiful pearly play of light that marks
these lovely fishes, as distinguished from the light reflected
by an uniformly polished surface. I have found the pearly
pigment of the scales to be provided with similar spicula in
fishes widely differing in size, structure, and habits ; as
the Gudgeon and Minnow, the Pike and the Marine Bream.
The spicula of these fishes agree in general form with those
of the Gold-fish : and also in size, with the exception of
trifling variations in the comparative length and breadth.
The colouring matter is lodged in lengthened cylindrical
cells, arranged side by side, and running across the scale :.
that is, in a direction at right angles to the lateral line..
BLOOD. 25
CHAPTER IT,
BLOOD.
The microscope is daily becoming a more and more im-
portant aid to legal investigation. An illustration of this
occurred not long ago, in which a murder was brought
home to the criminal by means of this instrument. Much
circumstantial evidence had been adduced against him,
among which was the fact, that a knife in his possession
was smeared with blood, which had dried both on the
blade and on the handle. The prisoner strove to turn
aside the force of this circumstance by asserting that he
had cut some raw beef with the knife, and had omitted
to wipe it.
The knife was submitted to an eminent professor of
microscopy, who immediately discovered the following
facts : — 1. The stain was certainly blood. 2. It was not
the blood of a piece of dead flesh, but that of a living
1 »ody ; for it had coagulated where ic was found. 3. It was
not the blood of an ox, sheep or hog. 4. It was human
blood. Besides these facts, however, other important
ones were revealed by the same mode of investigation.
5. Among the blood were found some vegetable fibres.
6. These were proved to be cotton fibres, — agreeing with
those of the murdered man's shirt and neckerchief.
7. There were present also numerous tesselated epithelial
cells. In order to understand the meaning and the bear-
ing of this last fact, I must explain that the whole of the
internal surface of the body is lined with a delicate mem-
brane (a continuation of the external skin), which dis-
'26 EVENINGS AT THE MICROSCOPE.
•charges mucus, and is hence termed mucous membrane.
Now this is composed of loose cells, which very easily
separate, called epithelial cells ; they are in fact con-
stantly in process of being detached (in which state they
constitute the mucus), and of being replaced from the
tissues beneath. Now microscopical anatomists have
learned that these epithelial scales or cells, which are so
minute as to be undiscernible by the unaided eye, differ in
appearance and arrangement in different parts of the body.
Thus, those which line the gullet and the lower part of
the throat are tesselated, or resemble the stones of a pave-
ment ; those that cover the root of the tongue are
arranged in cylinders or tall cones, and are known as
columnar; while those that line some of the entrails
carry little waving hairs {cilia) at their tips, and are
known as ciliated epithelium.
The result of the investigation left no doubt remaining:
that with that knife the throat of a living human being,
which throat had been protected by some cotton fabric,
had been cut. The accumulation of evidence was fatal
to the prisoner, who without the microscopic testimony
might have escaped.
But what was there in the dried brown stain that
determined it to be blood % And, particularly, how was
it proved to be not the blood of an ox, as the prisoner
averred 1 To these points we will now give a moment's
attention.
With this fine needle I make a minute prick through
the skin of my hand. A drop of blood oozes out, with
which I smear this slip of glass. The slip is now on the
stage of the instrument, under a power of 600 diameters.
You see an infinite number of small roundish bodies, of
a clear yellowish colour, floating in a colourless fluid, but
so numerous, that it is only here and there, as near the
edges of the smear, that you can detect any interval in
their continuity.
BLOOD. 27
These bodies are what we frequently call the blood-
globules, or, more correctly, blood-disks ; since their form
is not globular, but thin and flat, like that of a piece of
money. The slightness of their colour is dependent on
their extreme thinness : when a larger number lie over
each other the aggregated colour is very manifest, as it
then becomes either full dark red, or bright rich scarlet ;
for to these disks blood is entirely indebted for its well-
known hue. The blood of all vertebrate animals is com-
posed principally of these bodies, which when once seen
are easily recognised again : the microscope then readily
determines whether any given red fluid or dried stain is
composed of blood.
The disks in the blood of Mammalia, or animals which
suckle their young, are circular or nearly so, and slightly
concave on both of the surfaces. On the other hand, in
Birds, Fishes, and Reptiles, their form is elliptical, and
the surfaces are flat, or slightly convex. This distinction,
then, will at once enable us to determine Mammalian
blood.* But to determine the various tribes of this great
class among themselves, we must have recourse to another
•criterion, — that of dimensions.
The blood-disks of Man nearly agree in size with those
of the Monkey tribe, of the Seals and Whales, of the
Elephant, and of the Kangaroo. Most other quadrupeds
have them smaller than in Man ; the smallest of all being
found in those animals which chew the cud. The little
Musk-deer of Java has disks not more than one-fourth as
large as the human, but these are remarkably minute ;
no other known animal approaches it in this respect :
those of the Ox are about three-fourths, and those of the
Sheep little more than half the human average.
Tables have been made out, showing the comparative
* The Camels among Mammalia, and the Lampreys among Fishes,
are exceptions to the above rule ; the former having ellijotical and
convex blood-disks, the latter circular and slightly concave.
28
EVENINGS AT THE MICROSCOPE.
size of these corpuscles in various animals, and such
tables are very useful ; but we must bear in mind that
the average dimensions only are to be looked for ; since
in any given quantity of blood under examination, we
shall not fail to see that some disks exceed, while others
come short of, the dimensions of the majority.
Generally speaking, the blood-disks in Birds and in
Fishes are about equal in size : their form is, however,
that of a more elongated ellipse in Birds than in Fishes.
They may be set down as averaging in breadth the dia-
meter of the human disks, while their length is about
half as much again, or a little more, in most Birds.
a Man.
d
BLOOD-DISKS.
b Blennv. c Frog.
,/ Newt.
It is in Reptiles that we meet with the largest disks,
and especially in those naked-skinned species, the Frogs
and Newts. A large species inhabiting the American
lakes — Siren lacertina — has disks of the extraordinary
size of l-400th of an inch long by l-800th broad, or about
eight times as large as those of Man, in linear measure.
Our common Newts afford us the largest examples
among British animals, but they do not reach above
half the size just mentioned.
Taking this drop of blood from my finger as a standard
of comparison, we find, on applying the micrometer, that
BLOOD. 29
the disks rim from l-2500th to 1 -5000th of an inch ; but
that the great majority are about l-3300th in diameter.
On these slides are samples of other kinds. This is the
blood of a Fish — the common Blenny or Shanny (Blen-
iilus pltolis). Here we see at once the oval form of the
disks ; their average is l-2800th by l-3300th of an inch.
Here is the blood of a Frog (Rana temporaria) ; these are
more than twice the size of the fish's ; for they average
l-1250th by 1-1 800th of an inch. And, finally, I can
show you a drop of blood from this Smooth-newt (Lisso-
triton punctatis). The large size of the disks is now
plainly seen, and so indeed is the elegance of their form :
in this case, as in the last, we see in each disk a distinct
roundish nucleus. These run from l-703th to l-950th in
length by 1-1 100th to 1-1 600th in breadth; but the
average are about 1 -800th by 1-1 300th of an inch.
It may interest you to see these blood-disks in their
proper situation, and to observe the motion which they
possess during the life of their owners. It is, indeed, one
of the most instructive modes of using this wonder-work-
ing instrument to look through it at living structures, and
watch thet differen processes of life as they are carried on
under our eyes. Nor is this at all difficult to accomplish ;
for a large number of animals are so small that we can
•easily put them upon the stage of the microscope ; and
are withal so transparent that their coverings and various
tissues offer little or no impediment to our discerning the
forms and movements of the contained viscera. And in
•cases where the entire animal is too large to be viewed
under the microscope as a whole, it sometimes happens
that, by a little contrivance, we can so secure the creature
as to look without interruptionon certain parts of the body
which afford the requisite minuteness and transparency.
I have here a living Frog. You perceive that the web
which connects the toes is exceedingly thin and trans-
lucent, yet arteries and veins meander through its delicate
30 EVENINGS AT THE MICROSCOPE.
tissues, which are then clothed on both surfaces with the
common skin. But you ask how we can induce the Frog
to be so polite as to hold his paw up and keep it steady
for our scientific investigation. We will manage that
without difficulty.
Most microscopes are furnished (among their accessory
apparatus) with what is called a frog-plate, provided for
this very demonstration. Here is mine. It is a thin
plate of brass, two inches and a half broad and seven long,
with a number of small holes pierced through it along
the margins, and a large orifice near one end, which is
covered with a plate of glass. This is to be Froggy's bed
during the operation, for we must make him as comfort-
able as circumstances will admit.
Well, then, we take this strip of linen, damp it, and
proceed to wrap up our unconscious subject. When we
have passed two or three folds round him, we bind a tape
round the whole, with just sufficient tightness to keep him
from struggling. One hind-leg must project from the
linen, and we now pass a needle of thread twice or thrice
through the drapery and round the small of this free leg,
so as to prevent him from retracting it.
Here then he lies, swathed like a mummy, with one
little cold foot protruded. Lay him carefully on the brass
plate, so that the webbed toes shall stretch across the
glass. Now, then, we pass another tape through the mar-
ginal holes, and over the body, to bind it to the brass ; of
course taking care not to cut the animal, but only using
just as much force as is needful to prevent his wrigglings.
Now a bit of thread round each toe, with which we tie it
to as many of the holes, so as to expand the web across
the glass. A drop of cold water now upon the swathes to
keep him cool, and a touch of the same with a feather
upon the toes to prevent them from drying (which must
be repeated at intervals during the examination)— and he
is read v.
BLOOD. 3 ?
What a striking spectacle is now presented to us, as
with a power of 300 diameters we gaze on the web of the
foot ! There is an area of clear colourless tissue filling
the held, marked all over with delicate angular lines, some--
thing like scales ; this is the tesselated epithelium of the
surface. Our attention is caught by a number of black
spots, often taking fantastic forms, but generally some-
what star-like ; these are pigment cells, on which the
colour of the animal's skin is dej)endent. But the most
prominent feature is the blood. Wide rivers, with tor-
tuous course roll across the area, with many smaller
streams meandering among them ; some pursuing an inde-
pendent course below the larger, and others branchingout
of them, or joining them at different angles. The larger
rivers are of a deep orange-red hue, the smaller faintly
tinged with reddish-yellow. In some of these channels
the stream rolls with a majestic evenness ; in others it
shoots along with headlong impetuosity ; and in some it is
almost, or even quite, stagnant. By looking with a steady
gaze, we see that in all cases the stream is made up of a
multitude of thin reddish disks, of exactly the same dimen-
sions and appearance as those we saw just now in the
Frog's blood; only that here, being in motion, we see very
distinctly, as they are rolled over each other, that they are
disks, and not spherules ; for they forcibly remind us of
counters, such as are used for play, supposing they were
made out of pale red glass.
It is charming to watch one of these streams: selecting
one of medium size, where the density is not too great to
see the individual disks, and, tixing our eye on the point
where a branch issues from one side of the channel, mark
the disks shoot by one after another, some pursuing the
main course, and others turning aside into the branch,
perhaps so small as to allow of only a single disk to pass
at once.
The streams do not pursue the same uniform direction.
EVENINGS AT THE MICROSCOPE.
The larger ones do indeed ; and their course is from th
extremity of the toes towards the body : these are the
veins ; but the smaller streamlets flow in any direction,
and frequently send out side-branches, which presently
return into the stream from which they issued, or unite
with others in a very irregular net-work. These are the
capillaries which feed
the veins, and which
are themselves fed by
the arteries, who»e
course is in the oppo-
site direction, viz.,
from the body. These,
however, are with dif-
ficulty seen : they are
more deeply seated in
the tissues, and are
less spread over the
webs, being generally
placed along the bor-
ders of the toes : they
are, moreover, fewer
and smaller than the
veins ; but the blood
in them usually flows with more impetuous rapidity.
The variations in the impetus of the current which we
observe in the same vessel are probably owing to the men-
tal emotions of the animal ; alarm at its unusual position,
and at the confinement which it feels when it endeavours
to move, may suspend the action of the heart, and thus
cause an interruption in the flow ; or analogous emotions
may quicken the pulse. We will, however, now release
•our little prisoner, who, though glad to be at liberty, is. as
you see, none the worse for his temporary imprisonment.
Let us now look at the circulation of the blood in one of
the Invertebrate Animals. In this thin glass cell of sea-
CIECULATION IN FROG S FOOT.
BLOOD.
33
water is a small fragment of sea- weed, and attached to one
of its slender filaments you may see three or four tiny
knobs of jelly, clustered together like a bunch of grapes.
These are animals ; each endowed with a distinct life, but
associated together by a common stalk, which maintains
the mutual vital connexion of the whole. It is one of
the Social Tunicata, and is named Perophora Listeri.
Though each globose knob is no larger than a small
pin's head, it is full of organs which carry on the various
functions of life ; and, because the whole tissues are as
transparent as crystal, they allow us to watch the
processes with perfect ease. Take a peep at it.
It is a gelatinous sac, of a form intermediate between
globular and cubi-
cal, flattened on
two opposite sides,
with a sort of wart
at the summit and
another at the side,
each of which is
pierced with a
pursed orifice. The
upper of these ori-
fices admits water
for respiration and
food ; the latter
passes through
a
digestive system,
and is discharged
through
the side
PEROPHOKA.
orifice. The di-
gestive organs lie on that flattened side which is farthest
from your eye, and are therefore dimly seen.
The globose body is enclosed in a coating of loose shape-
less jelly, that passes off from one of the lower corners
.and forms a short foot-stalk, which unites with similar
34 EVENINGS AT THE MICROSCOPE.
foot-stalks from the sister globules, and all together are
attached to the sea-weed. Each foot-stalk has an organic
core, into which a vessel passes from the body.
Your attention is first arrested by the breathing sac,
with its rows of oblong cells, all in wheel-like motion. It
is indeed a wonderful object ; but for the present neglect
this, as we will return to it shortly, and direct your con-
sideration to the course of the blood.
It is true the fluid which I so name is not red, like
that of the Frog which you have just been gazing at, nor
does it carry disks of the same elegantly regular form.
But you have the advantage here of tracing, at one view,
the whole course of the circulation, from its first rush
out of the heart, to its return into that organ again.
At the bottom of the interior, below the breathing sac,
there is an oblong cavity, through whose centre there runs
a long transparent vessel, formed of a delicate membrane,
the appearance of which resembles that of a long bag,
pointed (but not closed) at either end, and then twisted in
some unintelligible manner, so as to make three turns.
This is the heart ; and within it are seen many minute
colourless globules, floating freely in a subtle fluid : this is
the nourishing juice of the body, which we may, without
much violence, designate the blood. Now see the circula-
tion of this fluid. The membranous bag gives a spasmodic
contraction at one end, and drives forward the globules
contained there ; the contraction in an instant passes on-
ward along the three twists of the heart (the part behind
expanding immediately as the action passes on), and the
globules are forcibly expelled through the narrow but open
extremity. Meanwhile, globules from around the other
end have rushed in as soon as that part resumed its usual
width, which in turn are driven forward by a periodic
repetition of the contraction and expansion of the heart.
The globules thus periodically driven forth from the
heart, now let us watch, and see what becomes of them.
BLOOD. 35
They do not appear to pass into any defined system of
vessels that we may call arteries, but to find their way
through the interstices of the various organs in the
general cavity of the body.
The greater number of globules pass immediately from
the heart through a vessel into the short foot-stalk, where
they accumulate in a large reservoir; but the rest pass up
along the side of the body, which (in the aspect in which
we are looking at it) is the right. As they proceed (by
jerks, of course, impelled by the contractions of the heart),
some find their way into the space between the breathing
surfaces, through narrow slits along the edges of the sac
and wind along between the oval ciliary wheels, which
we will presently consider. Besides these, however, other
globules wind along between the outer surfaces of the
sac and the inner surface of the body-walls.
But to return to the current which passes up the right
side : arriving at the upper angle of the body, the stream
turns off to the left abruptly, principally passing along a
fold or groove in the exterior of the breathing sac until
it reaches the left side, down which it passes, and along
the bottom, until it arrives at the entrance of the heart,
and rushes in to fill the vacuum produced by the expan-
sion of its walls after the periodic contraction. This is
the perfect circle ; but the minor streams that had forked
off sideways in the course, as those within the sac for
example, find their way to the entrance of the heart by
shorter and more irregular courses.
One or two things connected with this circulatory system
are worthy of special notice. The first is, that its direc-
tion is not constant, but reversible. After we have watched
this course followed with regularity for perhaps a hundred
pulsations or so, all of a sudden the heart ceases to beat,
and all the globules rest in their circling course, that we
had supposed incessant. Strange to behold, after a pause
of two or three seconds, the pulsation begins again, but at
D 2
36 EVENINGS AT THE MICROSCOPE.
the opposite end of the heart, and proceeds with perfect
regularity, just as before, but in the opposite direction.
The globules, of course, obey the new impulse, enter at
their former exit, and pass out at their former entrance,
and perform their circulation in every respect the same
as before, but in the reverse direction.
Those globules that pass through the vessel into the
foot-stalk appear to accumulate there as in a reservoir,
until the course is changed, when they crowd into the
heart again, and perform their grand tour. Yet there is a
measure of circulation here, for even in the connecting
vessel one stream ascends from the reservoir into the
body, as the other (and principal one) descends into it
from the heart ; and so, vice versa.
I have spoken of these motions as being performed
with regularity ; but if you look closely, you will see that
this must be understood with some qualification. The
pulsations are not quite uniform, being sometimes more
languid, sometimes more vigorous ; perhaps forty beats
in a minute may be the average ; but I have counted
sixty, and, presently after, thirty; I have counted twenty
beats in one half-minute, and only fifteen in the next.
The period during which one course continues is equally
uncertain ; but about two minutes may be the usual time.
Sometimes the pulsation intermits for a second or so, and
then goes on in the same direction ; and sometimes there
is a curious variation in the heart's action, — a faint and
then a strong beat, a faint and a strong one, and so
alternately for some time.
The phenomena of respiration are so closely connected
with those of circulation that it is not at all out of the way
to turn from the latter to the former; not to say that it
would be high treason against scientific curiosity if I were
to remove this object without explaining to you that mar-
vellous play of wheels that occupies the largest part of the
area that you behold. As you look on the globe, you ob-
BLOOD. 37
serve, hanging down from the upper extremity, and reach-
ing nearly to the bottom in one direction and almost from
side to side in another, a transparent square veil, which
is indeed a flat membranous bag, having its sides pretty
close together, with small openings along its edges, and
an orifice at the bottom leading into the stomach.
The mouth of this sac is in close connexion with the
upper or principal orifice, and therefore receives the
water, which is constantly flowing in, while that aperture
is expanded. This fluid then bathes the whole interior
of the sac ; but a portion of it escapes by the lateral
openings into the cavity of the body, between the sac
and the mantle, and is discharged through the secondary,
or side orifice.
The inner surface of this transparent sac is studded
with rings of a long oval figure, set side by side in four
rows. These rings appear to consist of a slight elevation
of the general membranous surface, so as to make little
shallow cells, the whole edges of which are fringed with
cilia, whose movements make waves, that follow each
other round the course in regular succession. In truth it
is a beautiful sight to see forty or more of these rings, all
set round their interior with what look like the cogs on a
watch wheel, dark and distinct, running round and round
with an even, moderately rapid, ceaseless motion. These
black running figures, so like cogs and so well defined as
they are, are merely an optical delusion ; they do not
represent the cilia, but merely the waves which the cilia
make : the cilia themselves are exceedingly slender close -
set hairs, as may be seen at the ends of the ovals, where a
slight alteration of position prevents the waves from taking
the tooth-like appearance. Sometimes one here and there
of the ovals ceases to play, while the rest continue ; and,
now and then, the whole are suddenly arrested simultane-
ously, as if by magic, and presently all start together again,
which has a most charming effect. A still more singular
38 EVENINGS AT THE MICROSCOPE.
circumstance is, that while in general the ciliary wave runs
in the same direction in the different ovals, there will be
one here and there in which the course is reversed ; and T
think that the animal has the power of choosing the direc-
tion of the waves, of setting them going and of stopping
them, individually as well as collectively.
The object of these ciliary wheels is to keep up a con-
stant current in the water. This fluid, as I have said,
enters from without, through the upper orifice of the body,
and is hurled over the whole surface of the breathing sac
by means of the ciliary waves, parting with its oxygen, as
it goes, to the blood, which streams, as we saw, every-
where between the rows of wheels. But the water has
another function : it carries particles of organic matter
with it, which are suitable for the nourishment of the
creature; these atoms are carried by the currents to the
bottom of the sac, and are poured into the stomach, where
they are digested ; the remains, together with the waste
water, being discharged through the lateral orifice.
Thus we see how closely connected are the three great
processes of circulation, respiration, and digestion.
MOLLUSC A. 39
CHAPTER III.
MOLLUSCA : THEIR SHELLS, TONGUES, EYES, AND EARS.
One of the most interesting aspects of microscopic study
is that in which it reveals the intimate structure of objects,
which, to the unassisted eye, appear simple or nearly so,
but which prove by the aid of magnifying power to be
complex. Thus we are often introduced to very curious
contrivances (if I may use such a word in reference to the
works of God), by which difficulties are overcome, and
substances, which would seem at first wholly unfit for
certain duties, are in the most admirable manner adapted
to fulfil them.
The combination of strength and lightness is always a
difficult problem in human art ; its successful solution
always excites our admiration. In the Divine mechanics,
too, it is very often required, and the variety of modes in
which it is accomplished are in the highest degree novel
and suggestive. We lately saw one of these in the struc-
ture of a feather, in the contrivance by which extreme
lightness of material was made, by a most remarkable
arrangement, to offer a firm resistance to opposing force.
I have now another example to show you, in which a
material, in itself heavy, is by its arrangement made very
light, while it preserves its strength.
You have seen many times, when walking along the
yellow sands kissed by the rippling waves, the shell, or
bone, as it is sometimes called, of the Cuttle-fish. You
know that it consists of a shallow boat-shaped shell, the
hollow of which is filled with a white substance, which can
40 EVENINGS AT THE MICROSCOPE.
be scraped away even with the finger-nail, and which
is sometimes used as pounce, to rub on paper from which
writing has been erased. It is this substance of which I
mean now to speak.
The possessor of this structure is a member of the
numerous class Mollusca,* which are generally charac-
terised by being inclosed in shells. Now shell, as we
all knowr is a solid, stony substance, much heavier than
water ; take into your hand that large Cassis on the
mantel-piece, and observe its great weight and compact-
ness. It is, in fact, real limestone; differing from that of
the rocks only in this, that it has been deposited by the
living organic cells of an animal, and arranged in a de-
finite form. We will presently examine other examples.
The " cuttle-bone " is a shell, not indeed inclosing the
animal, but inclosed by it, being contained within a
cavity in the substance of the fleshy mantle ; cut open the
mantle, and the shell instantly drops out.
The Cuttle is a rapid swimmer through the open sea.
A shell so large as this, if solid and compact like that of
the Cassis, would condemn it to grovel on the bottom, and
frustrate all the instincts of its nature. On the other
hand, it needs the strength and support of a solid column.
Wonderful to tell, the calcareous f shell is made not only
to be no hindrance to its swimming, but to contribute
greatly to its buoyancy : it is what the string of corks is.
to the bather who cannot swim, it is afloat. Throw this
entire cuttle-shell into water ; it floats on the surface as-
buoyantly as if it were actually carved out of cork.
I cut with a keen knife a little cube out of the shell,,
and, fixing it on the end of the revolving stage-needle,
apply a low power, say seventy diameters, using reflected
* From the Latin mollis, soft ; a name given by Cuvier to this
class from their bodies being always soft, whether bearing shells or
not.
T From calx, Latin for lime.
MOLLUSCA I THEIR SHELLS.
41
light. We are looking now at the perpendicular section ;
is it not a beautiful object1? you might fancy yourself
looking at one of the noble icebergs that majestically
navigate the polar seas, when it is rendered porous and
laminated by the rains of spring. You see a number of
thin horizontal tiers
or' stages, perfectly
parallel and equi-dis-
tant, about one-for-
tieth of an inch apart,
rising above each
other like the floors
of an editice. These
are connected to-
gether by an infinite
multitude of thin
pillars of crystal, or
rather leaves, some of
which show their edges towards us, others their broader
sides, and others are broken off at various distances, the
fragments standing up from the floor, or depending from
the roof, like stalactites and stalagmites in a cavern.*
This whole series of crystal floors and supporting plates
is formed of calcareous matter, — limestone, in short ; but
though the latter are set in such close array that the eye
cannot penetrate to any appreciable distance between
them, their extreme thinness renders the whole structure
very light, the interstices being occupied by air.
But now if I give the stage-needle half a revolution, we
shall have the horizontal section presented to the eye. In
this aspect we acquire much more information as to the
structure. The cut has been made very close to one of
CUTTLE-SHELL.
a Perpendicular. b Horizontal.
* In calcareous districts the water trickling through into caverns
often forms shapeless masses on the floor or hanging like icicles from
the roof; in the former case they are called stalagmites, in the latter
stalactites.
42 EVENINGS AT THE MICROSCOPE.
the horizontal floors, which we see marked all over with
a great number of lines, each of which runs hither and
thither, in a very sinuous pattern. The lines are made
up of a brilliant sparkling substance ; they are, in fact,
the basal portions of what we saw in the other section
as thin perpendicular plates ; I have cut oft* the plates
close to the bottom, and what we see is their insertion
into the floor.
Thus we perceive that what we took for a multitude of
plates, were but the various doublings and infoldings of a
single plate of great length, running quite across the
floor : an arrangement by which the strength of the ma-
terial is greatly augmented. You have often seen the
mode in which light walls are made of corrugated iron,
especially at railway stations; and are doubtless aware that
the corrugation, or bending in or out, imparts a strength
to it which the mere sheet iron, if set up as a smooth,
plane surface, would in no wise possess. The principle is
exactly the same in the two cases ; but the corrugation of
the limestone plates in the cuttle-shell is far more perfect
than that of the iron ; added to which there is the other
advantage, that the aggregate mass of material is made
highly buoyant by the large bulk of empty space that
intervenes between the sinuous folds of the crystal plates.
It may be interesting to compare with this the structure
of the more solid shells of bivalves, which have been so
elaborately studied by Dr. Carpenter. In general, these
consist of two very distinct layers, well seen in the valve
of the Pearl Oyster and its allies. The Pinna, or Wing-
shell, the largest of our native bivalves, affords us a good
example, especially of the external layer, since here this
layer projects beyond the inner one, in thin transparent
edges, which gives us an opportunity of examining their
structure without any artificial preparation. This frag-
ment, taken from the edge of one of those leafy expan-
sions, we will examine with a low magnifying power.
MOLLUSCA : THEIR SHELLS.
43
Each oHts surfaces has a sort of facetted, or honeycombed
appearance ; and the broken edges, which even to the
naked eye appear fibrous, are seen to resemble a number
of basaltic columns. " The shell 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."*
SECTIOX OF SACKE FROM 1'EAKL OYSTEK.
The inner layer of such shells is remarkable for pos-
sessing in different degrees the property of reflecting rain-
bow-like colours, often with great delicacy and splendour ;
and this is termed nacre, or familiarly " mother-of-pearl."
This iridescent lustre depends, as Sir David Brewster has
shown,f upon a multitude of grooves or fine lines, which
run in a very waved pattern, but nearly parallel to each
other, across the surface of the nacre. " As these lines
are not obliterated by any amount of polishing, it is
Carpenter, " The Micro cope," 590. + " Phil. Trans.," 1814.
44 EVENINGS AT THE MICROSCOPE.
obvious that their presence depends upon something pe-
culiar in the texture of this substance, and not upon any
mere superficial arrangement. When a piece of nacre is
carefully examined, it becomes evident that the lines are
produced by the cropping out of lamina? of shell, situated
more or less obliquely to the plane of the surface. The
greater the dip of these lamina?, 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 aptly compared by Sir J. Herschel to the
surface of a smoothed deal board, in which the woody
layers are cut perpendicularly to their surface in one part,
and nearly in their plane in another." *
Those beautiful objects, — so much prized for personal
adornment, — pearls, are concretions accidentally formed
within the shells of such mollusks, and are wholly com-
posed of the inner layer. Drs. Kelaart and Mobius have
recently published some highly interesting observations
on the causes both of the iridescence and of the pearly
lustre ; and these I will cite from the abstract trans-
lation of them made by Mr. Dallas.
" The surface of pearls is not perfectly smooth, but
covered with very fine microscopic elevations and depres-
sions. These are more or less irregular in their altitude,
but approach most nearly to equality in pearls of the
finest water. In pearls which exhibit a certain iridescence,
and which, when turned in different directions towards
the eye, present even very faint bluish, greenish, and red-
dish tints, the surface is found to present delicate irregular
curved furrows, which either run tolerably parallel to each
other, or form small irregular closed curves. This is due
to the mode of growth of the pearl, in which thin layers
* Carpenter, "The Microscope," 5<H.
MOLLUSCA : THEIR SHELLS. 45
of nacre, of small dimensions, have been laid over each
other. There is no continuous layer over the pearl, but a
number of small portions which sometimes overlie the
margins of the subjacent layers, and sometimes leave
them uncovered. This structure is seen most distinctly
in the pearl shell, where the conditions are rendered more
simple by the layers being deposited on a flat, or but
slightly curved surface. The distance of the furrows from
each other is not always the same ; sometimes they may
be recognised with the simple lens, while on other parts
they approach within —J^th of an inch of each other.
That the iridescence of nacre, or the nacreous colour, as
distinguished from pearly lustre, is caused by the inter-
ference of the light reflected from these furrows and the
intervening edges of the strata, is proved by the circum-
stance, ascertained by Brewster, that impressions of
mother-of-pearl taken in red or black sealing-wax exhibit
the same phenomena of colour distinctly. In pearls, in
consequence of their spherical form, the different masses
of coloured light are so diffused that they unite to form
white light; and this takes place with the greater perfec-
tion in proportion as the furrows are lost, and become
converted into a surface of fine elevations and depres-
sions.
" For their lustre, pearls are indebted to their being
composed of fine layers, which allow light to pass through
them ; whilst the numerous layers, lying one under the
other, disperse and reflect the light in such a manner that
it returns and mixes with that which is directly thrown
back from the outer surface. It is the co-operation of
light reflected from the surface, with light dispersed and
reflected in the interior, that gives rise to lustre ; for this
reason the knots of window-glass exhibit pearly lustre, and
the membranes of pearls deprived of their line are almost
as lustrous as solid pearls, except that their whiteness is
destroyed. ' The two masses of light entering the eye, act
46 EVENINGS AT THE MICROSCOPE.
upon it from different distances. Now, as it adapts itself
to the body seen through the transparent layer, it cannot
distinctly see the light reflected from the surface, and
the consciousness of this infinitely perceptible reflection
produces the phenomena of lustre.' * The thinner and
the more transparent the layers of which the pearl
consists, the more beautiful is its lustre ; and in this
respect the sea-pearls excel those of our river-mol-
lusks." f
We will pass now, by an easy transition, from the shells
of the Mollusca to their tongues. Who that looks at the
weather-worn cone of the Limpet, as he adheres sluggishly
to the rock between' tide-levels, would suspect that he
carries coiled up in his throat a tongue twice as long-
as his shell 1 And that this tongue is armed with thou-
sands of crystal teeth, all arranged with the most consum-
mate art in a pattern of perfect regularity 1 It sounds
almost like a fable to be told that the great Spotted Slug,
which we sometimes find crawling in damp cellars, carries
a tongue armed with 2G,800 teeth ! Yet there is no doubt
of the fact.
You see on this slip of glass a very slender band about
two inches in length. This is the tongue of the common
Periwinkle. While it was in the living animal, its fore-
part occupied the floor of the mouth, whence it passed
down below the throat, and, turning towards the right
side, formed a close spire of many whorls, exactly like a
coil of rope, which rested on the gullet. Here we have
it extracted, uncoiled, cleansed, and affixed to a slip of
glass for microscopical examination.
Only a small portion of the band is visible at a time
with such a power as is necessary to display the structure;
but by means of the stage-movement we can bring the
whole in succession under the eye, and discover that, with
some modifications of form, the same essential plan of
* Dove, " Farbenlehre," 117. t "Ann. & Mag. N.H." ; Feb. 1S58.
MOLLUSCA I THEIR TONGUES. 47
structure, and even the same elements, exist throughout.
Concentrating our attention on a single transverse series
of the numerous curved lines that at first sight bewilder
the mind, we perceive, by delicate focussing, that the
object before us consists of a number of hooks projecting
from the surface of the translucent band, and arching
downward. In this case a single row consists of seven
such hooked plates or teeth ; one in the centre and three
on each side. Each hooked plate has its arching tip cut
into five toothlets, of which the central one is the largest ;
and its base is united with the cartilaginous or gristly sub-
stance of the band. Only the middle plate is symmetrical ;
the lateral ones bend inwards towards the central one,
and are symmetrical only when considered in pairs, each
associated with its opposite. The plates are perfectly
transparent, but of a yellow horny colour; they are very
hard; and, as they are not dissolved by acids, it has been
supposed that their substance is siliceous (having the
nature of flint) ; but they are more probably chitinous, or
formed of the substance of which the hard parts of insects
are composed. The tongue before us has 600 rows such as
these, each, as we see, closely following, and indeed over-
lapping, its predecessor ; so that we can never look at a
single row without at the same time seeing others which
it overlaps, or by which it is overlapped.
The specimen which I will now show you is broader, but
shorter. It is the tongue of Trochus ziziphinus, a large
and handsome shell of regularly conical form, not un-
common on our rocky shores. It is perhaps a more
interesting study than that of the Periwinkle. There are
here, you observe, three constituent elements in the pat-
tern. First, a delicate glassy central tooth, tapering to a
fine point, and cut into minute saw-teeth along each edge.
Then a series, of five on each side, of similar glassy
pointed leaves, bending inward ; and outside these, on
either hand, are a great number of stout dark-coloured
48
EVENINGS AT THE MICROSCOPE.
hooks, arching forward and inward, each notched with
saw-teeth, and diminishing in thickness as they recede
from the centre.
The manner of using this elaborate organ is no less
curious than is its structure. During life it is only the
front portion — not more than one-third — of the band that
is in use ; this is spread out on the floor of the mouth,
with the teeth projecting and hooking backwards. The
remainder has its edges rolled over towards each other,
forming a tube closed at its extremity, which, as I have
e>
P ■■■■>>*■■
M
(
j
I
TOXGUE OF TROCHUS.
already observed, is coiled away (in the long-tongued
kinds) among the viscera.
The mode in which the tongue is used may be readily
seen by watching the actions of a Periwinkle in a marine,
or a Pond-snail in a fresh-water aquarium. When the
conferva has begun to form a thin green growth on the
glass sides of the tank, the Mollusca are incessantly en-
gaged in feeding on it, and rasping it away with this tooth-
ed band. "The upper lip with its mandible is raised ; the
ower lip expands; the tongue is protruded, and applied to
MOLLUSCA : THEIR TONGUES. 49
the surface for an instant, and then withdrawn ; its teeth
glitter like glass-paper, and in the Pond-snail it is so
flexible that frequently it will catch against projecting
points, and be drawn out of shape slightly as it vibrates
over the surface."*
Perhaps every variety is accompanied by some variation
in food or manner of feeding. With the Trochus, the pro-
boscis, a tube with thick fleshy walls, is rapidly turned
inside out to a certain extent, until a surface is brought
into contact with the glass, having a silky lustre: this is
the tongue; it is moved with a short sweep, and then the
tubular proboscis infolds its walls again ; the tongue dis-
appearing, and every filament of conferva being carried up
into the interior from the little area which had been swept.
The next instant, the foot meanwhile having made a small
advance, the proboscis unfolds again, the tongue makes
another sweep, and again the whole is withdrawn ; and
this proceeds with great regularity. I can compare the
action to nothing so well as to the manner in which the
tongue of an ox licks up the grass of the field, or to the
action of a mower cutting down swathe after swathe as he
marches along. The latter comparison is more striking,
on account of the marks of progress which each operator
leaves behind him. Though the confervoid plants are
swept off by the tongue of the Mollusk, it is not done so
cleanly but that a mark is left where they grew ; and
the peculiar form and structure of the tongue, which I
have above noticed, leave a series of successive curves all
along the course which the Mollusk has followed, very
closely like those which mark the individual swathes cut
by the mower in his course through the field.
The Periwinkle's table-manners differ slightly from
those of his relations. When he eats, he separates two
little fleshy lips, and the glistening, glass-like tongue is
seen, or rather the rounded extremity of a bend of it
* 'Woodward's "Mollusca," 161.
E
50 EVENINGS AT THE MICROSCOPE.
rapidly running round like an endless band in some piece
of machinery ; only that the tooth points, as they run
by, remind one rather of a watch-wheel. For an instant
this appears, then the lips close again, and presently re-
open, and the tongue again performs its rasping. It is
wonderful to see ; — perhaps not more wonderful than
any other of God's great works, never more great than
when minutely great; but the action and the instrument,
the perfect way in which it works, and the effectiveness
with which the vegetation is cleared away before it, all
strike the mind with more than usual force, as exhibitions
of the skill of the Creator.
As the Periwinkle moves along, mowing his sea-grass
as he goes, he carries before him two soft and flexible
horns, marked with zebra-like bands of black and white,
which he constantly waves about. These are organs of
some sense, probably of touch, and are therefore called
tentacles (or tryers) ; but they bear on their outer sides,
near the base, a pair of other organs, which are more
closely analogous to what we ourselves possess. You see
on each tentacle a little wart, which, when you look at it
with a lens, you perceive to have a round black glossy
extremity. This is the eye. By careful dissection under
the microscope, Ave find it to contain a beautiful trans-
parent crystalline lens, with a thick and glutinous vitreous
humour adhering to it behind, bounded by a retina or
curtain to receive the optic image, and an optic nerve.
But much more attractive you will find the eyes in
this little Scallop. It is a half -grown individual of what
is provincially known as the Squin (Pecten opercidaris),
much prized for its delicate flavour. Belonging to the
bivalve class of the Mollusca, the animal is inclosed
within two shallow shelly plates, concave internally and
convex externally, which are united by a hinge, just as the
works of a watch are protected by the case. When the
little creature is at its ease, as when the water is pure
MOLLUSCA : THEIR EYES. 51
and clear, it lies on one side, its valves being separated
as we see them now, a quarter of an inch or so apart
allowing us to discern what is contained between them.
Well, we see first a number of slender white pointed
threads, peeping out from each valve, and spreading on
all sides, waving hither and thither, groping, now contract-
ing, now expanding, with incessant but deliberate motion.
These are tentacles. If we trace them to their origin, we
find them attached to a fleshy sort of veil that lines each
valve to near its edge, and then abruptly falls at an angle
towards the opposite valve, where it meets a correspond-
ing veil. These two veils form the mantle. It is from
each of these that the tentacles spring ; and we discover
that there are four rows of these organs, one row set
along the angle, and one along the edge, of each veil.
But as we peer among these slender threads, our atten-
tion is riveted by some tiny points that are seated near
their bases, which glitter like brilliant gems. They are
seen only in those rows of tentacles which spring from
the angles of the veils, and not in those which fringe their
edges. Even the unassisted sight can detect the gleam
and glitter of these little specks ; but it is only when we
bring the lens to bear upon them that we see all their
beauty. Then they look like diamonds or emeralds, each
set in a broad ring of dark red substance, which greatly
enhances their beauty. They are inserted into the mantle
in the line of the tentacles, alternating with them, yet
not with absolute regularity, for there are more tentacles
than gem-points ; they are about half as numerous again
as the radiating ridges of the shell. Some are much
larger and more prominent than others, but they have
all the same structure and appearance.
These little organs are eyes. As its movements are far
more extensive, and more fitful and rapid than is common
in this class of animals, the little Pecten probably needs
these brilliant organs of vision to guide its wayward
e 2
52 EVENINGS AT THE MICROSCOPE.
rovings, as well as to guard it from hostile assaults. The
animal is very sensitive, withdrawing its tentacles and
mantle, and bringing the valves of its shell together, on.
any shock being given to the vessel in which it resides.
It manifests, however, a wisely measured degree of
caution, for it does not actually close the valves, unless
it be repeatedly disturbed, or unless the shock be violent,
contenting itself with narrowing the opening to the
smallest space appreciable ; yet even then the two rows
of gem-like eyes are distinctly visible, peeping out from
the almost closed shell, the tw^o appearing like one
undulating row from the closeness of their proximity.
If you are familiar with the pin-cushions which children
often make with a narrow ribbon round the edges of these
very Scallop-shells, you can scarcely fail to be struck
with the resemblance borne by the living animal to its
homely but useful substitute ; and the beautiful eyes
themselves might be readily mistaken for two rows of
diamond-headed pins, carefully and regularly stuck along
the two edges of the pin-cushion ribbon, — the ribbon itself
representing the satiny and painted mantle. A friend of
mine, to whom I was once showing this object compared
it, not inaptly, to a lady's ring set with diamonds.
You will not fail to remark how the position of these
beauteous organs is suited for their most extensive useful-
ness consistent with their safety. In the ordinary condi
tion of the animal's expansion, and especially when it i&
about to make its sudden and vigorous leaps, the gem-
like points are so situated as just to project beyond the
margin of the shell. So that when we view the creature
perpendicularly as it lies, our eyes looking down on the-
convexity of the upper valve, the minute eyes are seen, all
round its circumference, just, and but just, peeping from
under its edge. It is clear that this arrangement secures
to them the widest range of vision with the least possible-
exposure. As Divine contrivance has been often most
MOLLUSCA : THEIR EYES. 53
■deservedly recognised in the projection of the bony ridge
•over the human eye, which we call the brow, we surely
cannot fail to recognise, and admire it also, in the position
•of these delicate organs, either beneath the margin of the
solid shell, or, if projected, projected only in the smallest
•degree, and endowed with the power of retreating beneath
its barrier with the rapidity of thought on the least alarm.
There can be no doubt that these points, numerous as
they are, are true eyes, endowed with the faculty of vision
an a well-developed degree. For when their structure is
carefully examined by the skilful anatomist, each is found
to be covered with the proper sclerotic* tunic, which
•becomes a perfectly transparent cornea in front, and to
possess a coloured iris, — perforated with a well-defined
pupil, and connected with a layer of pigment which lines
ithe choroid tunic, — -a crystalline lens, and a vitreous
humour for the due refraction of the rays of light, and a
retina in their focus, formed by an expansion of the optic
aierve, and fitted to receive the picture ; the sensation of
which is then conveyed by an optic nerve from each eye
to the common nerve-trunk which runs along the border
of the mantle. Thus there exists in each of these lus-
trous points every element needful for the due performance
of vision; though, probably, the impressions thus con-
veyed may be neither so powerful nor so distinct as those
which are conveyed by the eyes of vertebrate animals.
They are, however, we may be sure, amply sufficient for
the wants of the pretty Scallop, and are fresh proofs of
the Divine wisdom and benevolence.
We have been accustomed from childhood to recognise
.as eyes the shining black extremities of the upper pair of
" horns " in the Garden Snail. And though some natu-
* The ball of the eye is composed of three coat* or tunics, the
sclerotic, choroid, and retina, and contains three humours, the aqueoits,
■vitreous, and crystalline. The cornea is the front part of the sclerotic,
tthe iris that of the choroid.
54
EVENINGS AT THE MICROSCOPE.
ralists have doubted, and even denied, that the tentacle
was anything more than a very delicate organ of touch,
yet it has been abundantly proved by dissection, and is
now incontrovertibly established, that its tip carries an
eye, even more completely developed than those of the
Pecten which we have just been looking at. The eye is
situated, not indeed on the very summit of the tentacle,
but on one side of a movable bulb there placed. It is
very minute, almost spherical, but slightly flattened in
front. It is protected by a very thin transparent layer of
the common skin, and is surrounded at the side and
behind by a perfectly black membrane, called the choroid,
or pigment-membrane. This black globule contains a
transparent and semi-fluid substance, with which it is
completely filled ; towards the bottom it is of thinner
consistence, and appears to contain many brilliant particles
when the eye is dissected under the microscope ; this may
be considered as the vitreous humour. In the front part
of the eye there is a crystalline lens, a small, circular,
nattish body, shaped like a lens, perfectly clear and trans-
lucent, but a little more solid than the vitreous humour.
Now protection for these so delicate organs is provided
in a way quite different from, yet equally effective with,
that which we just now admired in the case of the Pecten.
You know that if you touch, though ever so tenderly, the
eye of the Snail, it is instantly drawn into the horn by a
STRUCTURE OF EYE OF SNAIL.
most curious process of inversion. This action is per-
formed by means of a long muscular ribbon, which origi-
MOLLUSCA : THEIR EARS. 55
nates from the great muscle that retracts the head within
the shell, and which is inserted into the extremity of the
hollow tentacle. When this ribbon contracts at the will
of the animal, and still more forcibly when it is aided by
the contraction of the great head-muscle, the tip of the
tentacle with its eye is drawn within the surrounding parts,
just like the finger of a glove. When the animal would
again protrude its eye, the fibres which surround the
tentacle, like so many rings throughout its whole length,
successively contract, and thus gradually squeeze out, as
it were, the inverted part, until it is turned back to its
original position.
But the ears of this homely " creeping thing " are,
perhaps, even more curious than its eyes, though far less
elaborate in their structure. You will imagine now, that
I refer to the other pair of tentacles, as you are accus-
tomed to associate the idea of ears with projecting organs
situated on the head. No, you must not look there for
them. Here, in this young Garden Slug, which is so
small as to be conveniently examined on the stage of the
microscope, and so devoid of colour that we can readily
look through its tissues, — we shall easily find its ears,
though they are not quite so prominent as those of
an ass.
I subject the animal to a gentle pressure by means of
the compressoriurn,* just sufficient to flatten its soft body
a little, without injuring it. And now, with this low power,
you may see what Siebold, a learned zoologist and com-
parative anatomist, familiar with the curious phenomena
of life, truly calls " a wonderful spectacle." In the neck
of the little animal you discern, deep-seated in the soft
flesh, a pair of perfectly transparent globules, or capsules,
without any opening, but filled with a clear fluid, in which
there are some minute bodies performing the most extra-
* An instrument for compressing or flattening an object under the
microscope.
56 EVENINGS AT THE MICROSCOPE.
ordinary evolutions. They constantly keep up a series of
swinging or balancing movements, sometimes rotating,
sometimes forcibly driven in a certain direction, then in
the opposite, yet no single one ever by any accident
touching the walls of the capsule in which they are con-
tained. If the capsule be ruptured, the motions instantly
cease. These little bodies are of a calcareous nature ;
and they are called otolithes* that is, ear- stones. The
most that we know of these curious capsules, which
are indubitably ascertained to be organs of hearing, we
owe to the observations of the eminent zoologist just
named, and of this you may perhaps like to learn a
little.
Siebold says that a concentric depression is evident in
these otolithes, and that there may be seen in the centre
of the greater number of them a shaded spot, or rather a
minute aperture, which penetrates through the concretion
from the one flattened surface to the other. Subjected to
a strong pressure, the otolithes crack in radiating lines,
separating often into four pyramidal pieces. This separa-
tion also ensues, after a longer time, when the otolithes
are immersed in diluted nitric acid; and, if we touch them
with the concentrated acid, they suddenly dissolve with
the disengagement of a gas, whence Siebold concludes
them to be composed of carbonate of lime. The size of
the otolithes is not equal, and in the same capsule there
are always some which are smaller than others. Within
the capsule they have, during life, a very remarkable, and
in some respects peculiar, lively, oscillatory movement,
being driven about as particles of any light insoluble
powder might be in boiling water. The otolithes in the
centre have the appearance of being pressed together so
as to form a sort of solid nucleus, and towards this centre
the otolithes near the circumference seem even to be
* From the Greek ovg (ous), genitive Cjtoq (otos), an ear, and \i6oq
(lithos), a stone.
MOLLUSCA : THEIR EARS. 57
violently urged, their centripetal rush being invariably
repulsed, and as often driven again into a centrifugal direc-
tion. Removed from the capsule, the motions of the
otolithes instantly cease. The cause of these curious
oscillations remains undiscovered. Siebold could detect
no vibratile cilia on the surfaces of the capsule, and the
cessation of the motion when the otolithes are removed,
proves them to be unciliated themselves, and, at the same
time, distinguishes the motion from that of inorganic
molecules.
It has been, however, more recently ascertained that
the movements of the otolithes are due to very minute
cilia with which the interior surface of the capsule is
covered. This had been long suspected, and some eminent
23hysiologists, as Wagner and Kolliker, have distinctly
seen the cilia themselves.
If you ask what can be the use of ears to a class of
animals which are invariably dumb, I answer that though
this is true with respect to the great majority, yet it may
be only that our senses are too dull to perceive the delicate
sounds which they utter, and which may be sufficiently
audible to their more sensitive organs; and besides, some
Mollusca can certainly emit sounds audible by us. Two
very elegant species of Sea-slug, viz., Eolis punctata,
and Tritonia arborescens,* certainly produce audible
sounds. Professor Grant, who first observed the interest-
ing fact in some specimens of the latter which he was
keeping in an aquarium, says of the sounds, that " they
resemble very much the clink of a steel wire on the side
of the jar, one stroke only been given at a time, and
repeated at intervals of a minute or two; when placed
in a large basin of water the sound is much obscured,
and is like that of a watch, one stroke being repeated, as
before, at intervals. The sound is longest and oftenest
repeated when the Tritonia) are lively and moving about,
* Now called Dendronotus arlorescens.
58 EVENINGS AT THE MICROSCOPE.
and is not heard when they are cold and without any
motion ; in the dark I have not observed any light
emitted at the time of the stroke ; no globule of air
escapes to the surface of the water, nor is any ripple
produced on the surface at the instant of the stroke ; the
sound, when in a glass vessel, is mellow and distinct."
The Professor has kept these Tritonire alive in his room
for a month, and during the whole period of their
confinement they have continued to produce the sounds
with very little diminution of their original intensity.
In a small apartment they are audible at the distance of
twelve feet. " The sounds obviously proceed from the
mouth of the animal ; and at the instant of the stroke,
we observe the lips suddenly separate, as if to allow the
the water to rush into a small vacuum formed within. As
these animals are hermaphrodites, requiring mutual
impregnation, the sounds may possibly be a means of
communication between them ; or, if they are of an
electric nature, they may be the means of defending
from foreign enemies one of the most delicate, defence-
less, and beautiful Gasteropods that inhabit the deep." *
* "Edinb. Phil. Journ.," xiv. 18G.
SEA-MATS AND SHELLY CORALLINES. 59
CHAPTER IV.
SEA-MATS AND SHELLY CORALLINES.
When we were at the sea-side last summer we bought,
you may remember, of a poor widow whom we met on the
beach, a little basket of dried sea-weeds.
Now all of those objects were not sea-weeds. I mean
they were not all plants ; some of them are animals, and
these I wish to bring under your notice this evening for
our microscopical entertainment. Here are exquisitely
delicate crimson leaves, as thin or thinner than the thin-
nest tissue paper, with solid ribs and sinuous edges. Here
is a tall and elegant dark red feather, quite regularly pin-
nated. Here is a tuft of purple filaments as "fine as
silkworm's thread." And here is a broad irregular
expanse of the richest emerald green, crumpled and
folded, yet as glossy as if varnished.
Well, all of these are plants, certainly : they are veri-
table Algce, or sea-weeds. But here are other plant-like
objects of a pale brown, drab, or snowy-white hue. Let
us take this flattened brown leaf, divided into irregular
broad lobes; it looks almost like a thickish paper, and is
about as flexible. But pass your finger over it, and you
feel that its surface is evenly roughened ; and on close
and careful scrutiny you discern, even by the naked eye,
that its surface is covered with a delicate network of
minute shallow cells.
" Broad Hornwrack," and " Leafy Sea-mat," are the
names which the old collectors gave to this object ; and
60 EVENINGS AT THE MICROSCOPE.
^modern naturalists have given it the scientific appellation
of Flustra foliacea, and arranged it in the class Polt/zoa,
a group of animate beings, which have much of the form
of Polypes, and much of the structure of Mollusks.
We cut off a little piece from the end of one of the
lobes, and put this upon the stage of the microscope. We
now see that the cells are disposed in nearly parallel rows ;
but so that those of one row alternate with those of the
next, quincunx fashion, the middle of one cell being
opposite the end of its right and left neighbours; or like
the meshes of a net. The cells extend over the whole leaf,
and are spread over both its surfaces in this case ; the
united depth of two cells constituting the thickness of the
leaf-like structure. There are other species, more delicate,
which have but a single series of cells, all opening on the
same side of the leaf.
Each individual cell is shaped like a child's cradle; and
if you will imagine 20,000 wicker cradles stuck together
side by side in one plane, after the quincunx pattern I
have just mentioned ; and then the whole broad array
turned over, and 20,000 more glued on to these, bottom
to bottom, — you will have an idea of the framework of this
pale-brown leaf; dimensions of course, being out of the
consideration. The number may appear somewhat im-
mense, yet it is no larger than the ordinary average, as I
will soon show you. I measure off a square half-inch of
this leaf, which I carefully cut out with scissors; now with
the micrometer count the cells in the square piece. — You
find 60 longitudinal rows, each containing 28 cells, or
thereabouts. Very well ; a simple arithmetical process
shows that there are 1,680 cells in this square hal: inch ;
or 6,720 in a square inch. Now this very specimen,
before I mutilated it, contained an area of about three
square inches ; which would give 20,160 cells. This is
the number on one surface; the other contains an equal
aiumber ; and thus you see that I have not exaggerated
SEA-MATS AND SHELLY CORALLINES. Gl
the population of this tiny marine city. This, however,,
is by no means a specimen of unusual size.
These cells, which I compare to cradles, are of shallow
depth, but the head part rises to a much greater height
than the foot. All round this elevated portion the mar-
gin is armed with short blunt spines, two on each side,
which stand obliquely erect, projecting outwards over
the middle of the next cell, which thus, in concert with
the spines of the cell on the opposite side, they protect.
If you search carefully over the mass of cells with this
pocket-lens, you will perceive that on some of them are-
seated minute white globules, which look like tiny pearls.
These are not placed in any regular order, two being
sometimes found on contiguous cells, but generally thej
are scattered at more or less remote intervals. If we
now apply the microscope to these appendages, each glo-
bule is seen to be flat on that perpendicular side which
faces the foot of the cradle ; and this flat side is a
movable door, with a hinge along its lower edge. The
door is of a yellow hue ; the globule itself being, as I said,
of a pearly white hue.
This is all that we can see in this dried specimen ; but
if we had been fortunate enough to examine it when first
it was torn from its attachment to an old shell at the
bottom of the sea, you would have seen much more.
And what would then have appeared I will describe to
you.
Suppose, then, that a coverlid of transparent skin were
stretched over each cradle, from a little within the mar-
gin all round, leaving a transverse opening just in the right
place, viz., over the pillow, and you would have exactly
what exists here. There is a crescent-form slit in the
membrane of the upper part of the cell, from which the
semicircular edge, or lip, can recede if pushed from
within.
Suppose, yet again, that in every cradle there lies a
62
EVENINGS AT THE MICROSCOPE.
baby, with its little knees bent up to its chin, in that
zigzag fashion that children, little and big, often like to
lie in. But stay, here is a child moving ! Softly ! He
slowly pushes open the semicircular slit in the coverlid,
and we see him gradually protruding his head and
shoulders in an erect position, straightening his knees at
the same time. He is raised half out of bed, when lo !
his head falls open, and becomes a bell of tentacles ! The
baby is the tenant-polype !
"This is a very amusing romance," you say. Nay, it
is no romance at all. If you will excuse the homeliness of
the comparisons, I venture to affirm that a personal exa-
mination of the creature itself would justify their correct-
ness, and you would acknowledge that they could scarcely
be more apt.
Moreover, the globular chambers show signs of life ;
their front doors suddenly open, gape widely, and then
LEAFY SEA- MAT.
(A portion magnified.)
shut with a snap ; and presently this opening and shut-
ting is repeated. The meaning of this action you will
better understand when you see analogous organs in
SEA-MATS AND SHELLY CORALLINES. 63
another form of the same class of animals. Meanwhile,
I will just point out a beautiful though minute proof of
design in a point of the structure of the cells connected
with these pearly chambers. If you look closely, you
will see that the spines of the margin are not found on
those cells that carry the pearls ; and moreover, that they
are also wanting on the approximate edges of the two cells
that lie behind every such pearl-bearing cell. Now the
reason of this omission is obvious. The spines project-
ing obliquely would interfere with the gaping of the
door ; and hence they are invariably absent there.
I happen to have in my aquarium a living individual
of another species belonging to the same class, and agree-
ing with this in all essential particulars of structure, though
widely different in form. The difference, however, is
mainly dependent on a rather unimportant point of ar-
rangement ; for the cells, instead of being set side by side
and end to end, in quincunx fashion, to an indefinite
extent, on two surfaces of a plane, are disposed on one
single surface, and in longitudinal rows of two or three
cells abreast ; thus narrow ribbon-like branches are
formed, which now and then divide into two, then these
into two more, and so on. These branches thus become
fan-shaped, which, by being slightly curved, became seg-
ments of funnels ; and the peculiar elegance of this coral-
line consists in the mode in which these branches are set
on the stem, viz., in an ascending spiral curve, so that the
effect is that of several imperfect funnels set one within
another, but which yet you perceive, by turning the whole
gradually round, to compose a single corkscrew band of
successive fans. This whole structure stands upright in
its natural state, like a little compact shrub growing from
a root ; and as a good many are commonly associated
together, they form a sort of mimic grove, fringing the
sides of dark rocky sea-pools.
The species is called the Corkscrew Coralline, or some-
G4 EVENINGS AT THE MICROSCOPE.
times, the Bird's-head Coralline, the latter name being
assigned to it for a reason which you will presently per-
ceive. The appellation by which it is known to natura-
lists is Bugula avicularia.
We drop our specimen into a very narrow cell, com-
posed of parallel walls of thin glass, a very minute flat-
tened tank, in fact, such as can be put on the stage of
the microscope. Here, bathed in its native sea-water, as
clear as crystal, we shall see it opening and expanding
its numerous polypides with the utmost activity and
evident enjoyment.
You gaze ; but you know not what you see. The pre-
sence of many lines, representing transparent vessels of
strange and dissimilar shapes, overlying each other ; and
the swaying to and fro of curious objects, which strike
now and then forcibly across the field of view, are quite
bewildering. I must act the showman and tell you
what to see.
The cells are oblong, shaped much like a sack of corn,
with a spine ascending from each of the upper corners.
Each stands on the summit of its predecessor in the same
row, and side by side with those of its fellow-rows, in
such an order that the top of one cell comes opposite the
middle of the one beside it. The top of the sack is
rounded, and appears closed, but we shall presently find
an opening there. The broad side that faces inwardly has
a large elliptical transparent space occupying nearly its
whole surface; this is covered with a very thin and elastic
membrane, and answers a peculiar end. Just below one of
the spines that crowns the summit of the cell on one of the
edges, is situated a little lump, to which is attached, by a
very free joint, an object which you will perceive to bear a
remarkable resemblance to the head of a bird of prey. It
has a beak strongly hooked, with two well-formed man-
dibles, of which the lower is movable, shutting into the
cavity of the upper ; you observe it deliberately opening,
SEA-MATS AND SHELLY CORALLINES. 65
like that of a bird, only stretching to an enormous width
of gape, and then closing with a strong and sudden snap.
Now and then the whole head sways backward and for-
ward on its joints; and these movements, combined with
the fitful and apparently spiteful snappings, performed
by many birds' heads scattered about the branch, are
highly curious and amusing.
The birds' heads, however, are not the living inhabi-
tants of the cells ; they are not integral parts of them.
The cells have their proper inhabitants, each dwelling in
its own ; and each essentially formed on the same plan
as the "baby with the tucked-up knees," that makes the
Sea- mat for his cradle-house.
In order to get a good view of the tenant here, you
must move the stage about till you find that the branch
is presented to your eye sidewise. Directing your attention
then to the lateral edge of a single inhabited cell, its
summit is seen to protrude diagonally, towards the inner
side (i.e., towards the axis of the spire), a tubular mouth
which is membranous and contractile. When the animal
wishes to emerge, this tubular orifice is pushed out by
unfolding the integument, and the tentacles are exposed
to view, closely pressed into a parallel bundle; the un-
folding of the integument, that is attached at their base,
goes on till the whole is straightened ; when the tentacles
diverge and assume the form of a funnel, or rather that
of a wide-mouthed bell, the tips being slightly turned out.
They are furnished with a double row of short cilia in the
usual order, one set working upward, the other downward.
Their base surrounds a muscular thick ring, the entrance
to a funnel-shaped sac, the substance of which is granular,
and evidently muscular, for its contractions and expan-
sions are very vigorous, and yet delicate. Into this first
stomach passes, with a sort of gulp, any animalcule whirled
to the bottom of the funnel by the ciliary vortex ; and
from thence it is delivered, through a contracted, but still
F
66 EVENINGS AT THE MICROSCOPE.
rather wide gullet, into an oblong stomach, the lower
portion of which is obtuse. An extremely attenuated
duct connects this, which is probably the true stomach,
with a globular, rather small, intestine, which is again con-
nected by a lengthened thread with the base of the cell. By
an arrangement common to the ascidian* type of the diges-
tive function, the food is returned from the intestine into
the true stomach, whence the useless parts are discharged
through a wide and thick tube that issues from it close
behind the point where the gullet enters. This tube passes
upwards parallel to the gullet, and terminates by an
orifice outside and behind the base of the tentacles. All
these viscera are beautifully distinct and easily identified,
owing to the perfect transparency of the walls of the cell,
the simplicity of the parts, and their density and dark
yellow colour. All of them are manifestly granular in
texture, except the slender corrugated tube which connects
the stomach with the globose intestine : this is thin and mem-
branous, and is doubtless, if I may judge from analogy,
capable of wide expansion for the passage of the food-pellet.
The sudden contraction of the polypide into its cell
upon disturbance or alarm, and its slow and gradual
emergence again, afford excellent opportunities for study-
ing the forms, proportions, and relative positions of the
internal organs. In contraction, the globular intestine
remains nearly where it was; but the stomach slides down
into the cell behind it, as far as the flexible duct will
allow, and the thick gullet bows out in front, showing
more clearly the separation between it and the rectum,
and the insertion of both into the stomach. This retrac-
tion is, in part, effected by a pair of longitudinal muscular
bands, which are inserted at the back of the bottom-part
of the cell, and into the skin of the neck below the ten-
* The Ascidia are a low order of animals growing in masses in the
sea, with bodies like little leathern pouches : whence their name, from
a Greek word clctkoq (askos), meaning pouch.
SEA-MATS AND SHELLY CORALLINES. 67
tacles. The contraction of these bands draws in the
integument, like the drawing of a stocking within itself,
and forces down the viscera into the cavity of the cell,
which is probably filled with the vital juices.
Besides the hind bands, there is one, or a pair of
similar muscular bands attached on each side of the front
part of the base of the cell, and inserted similarly into
the neck. By watching the contraction of these, you will
be enabled to determine the use of the membrane-covered
aperture up the front of the cell. At the moment of the
retraction of the viscera into the cell, a large angular
membrane is forced outward from the front side, which
is protruded more or less in proportion to the degree of
withdrawal of the polypide ; and as the latter emerges
again, the membrane falls back to its place. It is evident,
then, that this is a provision for enlarging the cavity ; the
walls are horny, and probably almost inelastic; but when
the stomach forces the intestine forward, and the thick
gullet is bent outward by the withdrawal of the neck
and tentacles, the needful room is provided by the bulg-
ing out of this elastic membrane, which recovers its
place by the pressure of the surrounding water, when the
pressure of the fluids within is removed.
Now, after watching these movements of the polypides,
and the various structures whose forms and limits those
movements reveal, it will become manifest to you that
there is no visible organic connexion between the animal,
distinctively so called, and the curious bird's head. This
latter has a muscular system of its own, by means of
which its energetic motions are performed; but it appears
quite isolated on the outside of the calcareous cell, and
wholly cut off from the interior by the knob on which it
works, and by the thickness of the cell-wall. Both knob
and wall appear quite imperforate ; and yet we cannot
but presume that some connexion exists, perhaps through
the medium of an exceedingly delicate and subtile, but
f 2
68 EVENINGS AT THE MICROSCOPE.
living tissue, which may be presumed not only to line,
but also to cover the strong cell; just as the strong-
envelope and spines of a Sea-urchin are covered with
a thin film of living flesh.
The functions and use of these singular processes are
as obscure as their connexions with the animal. Yet, that
they play some important part, we may almost certainly
infer, from the general prevalence of similar or analo-
gous appendages among the various forms of this class.
The globular pearls which you lately saw on the Sea-mat
are but another form of bird's head ; and the falling-door
answers to the opening and shutting mandible. The
forms, indeed, of these organs are very diverse, and some-
times they are greatly disguised. But what about their
function 1 More than one observer has noticed the
seizure of small roving animals by these pincer-like beaks;
and hence the conclusion is pretty general, that they are
in some way connected with the procuring of food. But it
seems to have been forgotten, not only that these organs
have no power of passing the prey thus seized to the
mouth, but also that this latter is situated at the bottom
of a funnel of ciliated tentacles, and is calculated to re-
ceive only such minute prey as is drawn within the ciliary
vortex. I have ventured to suggest a new explanation.
The seizure of a passing animal, and the holding of it in a
tenacious grasp until it dies, may be a means of attract-
ing the proper prey to the vicinity of the mouth. The pre-
sence of decomposing animal substance in water invariably
attracts crowds of infusory animalcules, which then breed
with amazing rapidity, so as to form a cloud of living
atoms around the decaying body, quite visible in the
aggregate to the unassisted eye; and these remain in the
vicinity, playing round and round until the organic matter
is quite consumed. Now a tiny worm or other animal
caught by the bird's head of a Polyzoon,* and tightly held7
* From the Greek ttoXvq (polus), many, and Z,wov (animal). A name
SEA-MATS AND SHELLY CORALLINES. 69
would presently die ; and though in its own substance it
would not yield any nutriment to the capturer, yet by
becoming the centre of a crowd of busy infusoria, multi-
tudes of which would constantly be drawn into the ten-
tacular vortex, and swallowed, it would be ancillary to
its support ; and the organ in question would thus play
no unimportant part in the economy of the animal.
given to a certain group of animals which are, as it were, made up or
many individuals massed together. By some naturalists they are called
Bryozoa, a term derived from /3puor (bruon), sea-mos*7 and Z,Coov.
'0 EVENINGS AT THE MICROSCOPE.
CHAPTER V.
INSECTS : WINGS AND THEIR APPENDAGES.
I propose now to reveal to you some of the microscopic
marvels of the insect world ; a race vastly more populous
than all of the other animate tribes put together ; for the
most part so minute as to be peculiarly suitable subjects
for our present investigations, and so furnished with
elaborate contrivances and exquisite pieces of mechanism,
as to elevate our thoughts at every turn to the majesty of
the Divine wisdom displayed in the most minute of His
creatures. Let us begin with their wings.
The most perfect fliers in existence are Insects. The
swallow and the humming-bird are powerful on the wing,
and rapid ; but neither these nor any other " winged
fowl " can be compared with many of the filmy-winged
Insects. The common House-fly, for example, will remain
for hours together floating in the air beneath the ceilings
of our dwelling-rooms, hovering and dancing from side
to side, apparently without eflbrt and without fatigue.
It has been calculated that in its ordinary flight the
House-fly makes about 600 strokes with its wings every
second, and that it is carried through the air a distance
of five feet during that brief period. But, if alarmed,
the velocity can be increased six or seven fold, as every
one must have observed, so as to carry the insect thirty,
or five and thirty, feet in the second. " In the same
space of time," observes Mr. Kirby, "a race-horse could
clear only ninety feet, which is at the rate of more than
a mile in a minute. Our little fly, in her swiftest flight,
INSECTS : WINGS AND THEIR APPENDAGES. 7 1
will in the same space of time go more than the third of
a mile. Now compare the immense difference in size of
the two animals (ten millions of the fly would hardly
counterpoise one racer), and how wonderful will the
velocity of this minute creature appear ! Did the fly
equal the race-horse in size, and retain its present powers
in the ratio of its magnitude, it would traverse the globe
with the rapidity of lightning." *
Bees, again, are accomplished masters of aerial motion.
The Humble-bees, notwithstanding their heavy bodies,
are the most powerful fliers of this class. The same
excellent entomologist tells us that they " traverse the
air in segments of a circle, the arc of which is alternately
to right and left. The rapidity of their flight is so great
that could it be calculated, it would be found, the size of
the creature considered, far to exceed that of any bird,
as has been proved by the observations of a traveller in
a railway carriage proceeding at the rate of twenty miles
an hour, which was accompanied, though the wind was
against them, for a considerable distance by a Humble-
bee (fiombus siibinterrujrtus), not merely with the same
rapidity, but even greater, as it not unfrequently flew to
and fro about the carriage, or described zig-zag lines in
its flight. The aerial movements of the Hive-bee are
more distinct and leisurely." f
You have doubtless often admired the noble Dragon-
fly, with its four ample and wide-spread wings of gauze,
hawking in a green lane or over a pool in the noon of
summer. It sails, or rather shoots with arrowy fleetness
hither and thither, now forwards, now backwards, now to
the right, now to the left, without turning its body, but
simply by the action of its powerful and elegant wings.
Leeuwenhoek once saw an insect of this tribe chased by a
swallow in a menagerie a hundred feet long. The Dragon-
fly shot along with such astonishing power of wing, to the
* "Intr. to Entorr." ; Lett, xx f Ibid.
72 EVENINGS AT THE MICROSCOPE.
right, to the left, and in all directions, that this bird of
rapid flight and ready evolution was unable to overtake
and capture it, the insect eluding every attempt, and being
in general fully six feet in advance of the bird. A Dragon-
fly has been known to fly on board a ship at sea, the
nearest land being the coast of Africa, five hundred miles
distant, a fact highly illustrative of its power of wing.
It is a point of interest to know the structure of the
organs by which such results are accomplished, and there-
fore we will devote an hour to the microscopical examina-
tion of the wings of one or two insects. Let us begin
with the common Fly, one of which, a fine blue-bottle, is
somewhat noisily buzzing in the window ; —
" The blue-fly sung i' the pane/' —
as if to invite our attention to him. Well, we will
borrow one of his wings for the lesson ; and, putting it
into the stage-forceps, we shall be able to turn it in any
direction for observation beneath the microscope.
At first it seems a very thin transparent membrane, of
a shape between triangular and oval, with a few fine
black lines running through it, and along one edge. But
on bringing a greater magnifying power to bear on it, we
see that the clear surface is covered with minute short
stiff hairs, each of which has an expanded base. And
still further, by delicate focussing, we find that there are
two sets of these hairs, which come into view alternately,
those of one row projecting upward towards our eye,
those of the other downward. They are placed on both
the upper and under surfaces, and are in fact appendages
of two distinct membranes, applied to each other. There
is some reason to believe that these hairs are delicate
organs of touch, communicating impressions through the
skin to a sensitive layer beneath ; at least such seems
their function on the body, and we may judge from
analogy that it is not different here.
INSECTS : WINGS AND THEIR APPENDAGES. 76
The black lines are elastic, horny tubes, over which
the membranes are spread and stretched, like the silk of
an umbrella by its ribs. The upper membrane is firmly
attached to the tubes (which are called nervures); the
lower has but a slight adhesion, and is easily stripped
from them. The nervures originate in the body, and
diverge like a fan to various points of the tip, and to the
upper and lower edges; some of them, however, terminate
in the substance of the wing without reaching the edge,
and some send off cross branches by which two are con-
nected together. They generally maintain the same
thickness throughout ; but there are enlargements, where
the branches join the main trunks. These nervures are
hollow ; and are during life filled with a subtle fluid,
which is supplied from the vessels of the body. They
contain also ramifications of the exquisite spiral air-
vessels, which we shall presently consider, so that both
air and blood circulate in them.
But in this wing of a Bee all these structures may be
seen to greater advantage. The membrane appears per-
fectly uniform by transmitted light, even with so high a
magnifying power as 600 diameters, at least on a cursory
examination ; though, by careful manipulation, we may
discern faint traces of angular lines which divide the
whole surface into irregular areas. But, by using reflected
light at an oblique angle, this areolation, wrhich indicates
the primary cells of the structure, is much plainer, and
each area is perceived to carry a single hair in its centre.
The hairs themselves here take the character of curved
spines, not unlike those of a rose-bush. Along the front
edge of the wing they are straight, stout, densely crowded,
and overlapping in an inclined position ; but the most
interesting modification of these organs is seen at the front
edge of the posterior pair. Unlike the Fly, wrhich has but
a single pair of wings, the Bee has two pairs, of which the
fore pair is the larger and more horny, the hinder pair
74
EVENINGS AT THE MICROSCOPE.
DOUBLING AND HOOKS IX A BEE S WI>"G.
seeming to be, as it were, cut out of the hinder and inner
side of the fore ones. The two edsres — the hinder edo-e of
the fore pair and the
front edge of the hind
pair — then corre-
spond ; but it is neces-
sary that, during flight,
when the wings are ex-
panded, the two wings
on each side should
maintain this relative
position, neither over-
lapping the other, but
together presenting
one broad surface,
wherewith to beat the
air. There must be, therefore, some contrivance for
locking together the two edges in question, which yet
shall be capable of being unlocked at the pleasure of
the animal ; for the wings during repose slide over one
another. This contrivance is furnished by a series of
hairs or spines running along the front edge of the hind-
wing ; they are bent up into strong semicircular hooks,
arching outwards, looking, under a high power, like the
hooks on a butcher's stall. On the other hand, the margin
of the fore-wing is strengthened, and is turned-over with
a shallow doubling, so as to make a groove into which
the hooks catch ; and thus, while the fore-wings are ex-
panded, the hooks of the other pair are firmly locked in
their doubled edge ; while, as soon as flight ceases, and
the wings are relaxed, there is no hindrance to the
sliding of the fore over the hind pair.
The wings of many insects are interesting on account
of the organs with which they are clothed. A familiar
example is furnished by the common Gnat, a wing of
which is on the slide now before us. There is the same
INSECTS : WINGS AND THEIR APPENDAGES.
7a
general structure as before, — two clear elastic membranes
stretched over slender horny tubular nervures, and stud-
ded on both surfaces with short spine-like hairs, which
in this case, however, are very numerous and minute.
But, along the nervures, and along other lines which run
(generally) parallel with the front margin, and also along
the whole margin, there are set long leaf-like scales of
very curious appearance and structure.
Confining our attention to one of these lines, suppose
one of the nervures, we see that its course is marked on
the upper membrane by five rows of minute elevated
warts, arranged obliquely with one another. Erom each
of these warts springs a slender stem, which gradually
dilates into a thin leaf -shaped plate of transparent sub-
stance, having from four to eight or ten longitudinal ribs.
They project in a radiating manner, all inclined towards
the tip of the wing. The same line on the under-surface
carries the like number of leaf-like plates, corresponding
in arrangement, structure, form, and direction with those
on the upper side.
The margins of
the wing all round
are furnished with
similar organs,
with this difference,
that whereas the
plates along the
lines are, as it were, cut off abruptly at their greatest
diameter, the marginal ones converge again with a
gracefully curved outline, to a fine point : a form which
is seen to the greatest advantage along the hind edge of
the wing ; while those of the front margin are thicker,
and more densely crowded.
There are, however, other Insects which display these
or similar appendages in far greater profusion, and in
much variety of form and appearance. In the fissures or
SCALES ON A GNAT'S WING.
76
EVENINGS AT THE MICROSCOPE.
cliffs that border the sea-shore may often be found some
wingless but active Insects, which are endowed with the
power of leaping in great perfection. From their hinder
extremity being furnished with long projecting bristles,
they are sometimes called Bristle-tails, but naturalists
designate the genus Jfachilis. If you can get one suffi-
ciently still to examine it, you will be delighted with the
lustre of its clothing, which appears dusted all over with
a metallic powder of rich colours, — red, brown, orange
and yellow, foiled by dull lead-grey in places.
EBISTLE-TAIL.
(Slightly enlarged.)
If you touch one of these nimble leapers, though ever
so lightly, you will see the result on your linger-ends ;
for they will be found covered with a thin stratum of the
finest dust, which displays the coloured metallic reflections
seen on the insect. By touching one with a plate of glass
instead of your linger, you will get the same dust to
adhere to this transparent medium, by applying which
to the microscope you may at once discern the marvellous
nature of the raiment with which the little creature is
bedecked.
The dust is now seen to be composed of myriads of
thin scales, mostly regular and symmetrical in their forms,
though varying exceedingly among themselves in this re-
spect. Some are heart-shaped, some shovel-shaped, some
round, oval, elliptical, half-round, half-elliptical, long and
INSECTS : WINGS AND THEIR APPENDAGES.
« i
narrow, sometimes irregular and unequal, and of various
other indescribable outlines. Perhaps the most common
forms are ovate, heart-shaped, and like that of the pan
of a fire-shovel. Each thin scale has a minute foot-stalky
which is not connected with it at either extremity, but
at a point of one surface a little way from the smaller end,
whence it projects at an oblique angle ; so that when the
stalk was inserted in its proper cell in the skin of the
insect, the scale lay horizontally, covering the insertion.
This is a peculiarity not found in
some other scales that I shall pre-
sently introduce to you.
The whole body of the scale is
traversed by a series of fine close-
set parallel lines, running longitu-
dinally from end to end. At least
this is the ordinary arrangement ;
but occasionally you see scales, in
which there are two series of parallel
lines, arranged on either side of an
imaginary central line, towards which
they respectively converge,but never
I think, diverge from it. These lines
appear to form thickened ribs, but seem to be made by
elevations of the membrane both above and below. Be-
tween the ribs, on the larger scales, we see a number of
very delicate cross lines, which are probably regular
wrinklings of the depressed surface.
There is another little Insect of the same family, com-
monly found in cupboards, and in chinks of old damp
houses, and called the Sugar-louse (Lepisma); very much
like this, but of a silvery lustre, and carrying the three
bristles of the tail diverging widely. This also is covered
with scales, some of which are preserved on this glass
slide. Here, while the general appearance and structure
agree with those of the scales which we have just been
SCALE OF BRISTLE-TAIL.
78 EVENINGS AT THE MICROSCOPE.
considering, there is considerable diversity in details.
The form is usually ovate or shovel-like ; the foot-stalk,
projecting at a similar angle, is not set on the inferior
surface, but in the bottom of a deep narrow incision ;
and the ribs are invariably divergent like those of a fan.
In these, however, there is a peculiarity of arrangement,
which I have never seen noticed, but which is obvious
enough in the specimens before us. The ribs on the two
surfaces diverge at different angles, those of the upper
surface being the more divergent, standing out widely
from the foot-stalk, while those of the lower membrane
are coarser, and much more nearly parallel, their bases
ranging along the hind edge of the scale. The effect of
the intersection of the sets of lines at so acute an angle,
is to convey the optical impression that the scale is
covered with short irregular dashes.
Such is the arrangement on these scales, which I pre-
pared myself from the common Lepisma; but I have a
slide marked " Lepisma," from one of the dealers in
microscopic objects, in which the ribs on the two sides
concur ; but, on one side, there are obliquely divergent
lines visible only near the margin, which appear to be
produced by wrinkles of the membrane analogous to the
transverse dashes on those of Machilis.
Scales much more delicate than either of these sorts
are found on the Podura, a minute insect, of which there
are several species ; which leap, jerking out the bristles of
the tail, that are ordinarily carried under the body, like
a coiled spring. They are common in cellars, in hot-bed
frames, on dunghills, on the surface of water in road-
ruts, kc. On the slide before you are some of the smaller
scales from one of these insects ; they are exceedingly
delicate, and the clearness with which you discern the
character of their markings, is a proof of the good defini-
tion of your microscope; this is what is called a "test-
object." At first sight they seem covered with ribs like
INSECTS I WINGS AND THEIR APPENDAGES. / 9
those of the Machilis and Lepisma ; but, by the use of a
magnifying power of 600 diameters (as I have now put
on), you perceive that, in the first place, the lines are not
straight nor parallel, but curve irregularly, and are often
branched; and, in the second place, that they are not
uninterrupted, but made up of a series of successive
wedge-shaped warts, which lie nearly flat, but project a
little at the larger end, where each overlaps the next.*
The scale we are looking at measures "00 14: inch in
length, and '0009 in width; here the marks are well de-
fined; here are smaller scales *0008 in length by -00035 in
width, but these are more dim and difficult to resolve.
The beautiful and extensive order called Lepidoptera or
Scale-winged, par excellence, including the gay tribes of
Butterflies and Moths, present us with many exceedingly
interesting varieties in these singular coverings. The
study of these might be almost as wide as the immensity
of species; I can show you only a few examples.
Here are specimens from the pretty little white Five-
plume Moth (Pterophorus), so common in meadows in
summer. The general shape of the scales from the body
and wings is that of a willow-leaf, some singly pointed,
but more cut at the tip into two, three, or four notches.
Those from the legs are longer, and slenderer in propor-
tion; and among the others from the wings, there are
some which take the form of hairs, which send forth one
or more branches from one side, that form a very acute
angle with the main stem. The scales proper are all
* Mr. Richard Beck, using illumination under a power of 1,300 dia-
meters, with the binocular microscope, has satisfied himself that the
markings of the Podura scale " consist of a series of toothed ridges,
the profile of which might be said to resemble the edge of a saw." He
believes that the markings on this and all similar scales are " more or
less elevations or corrugations upon the surface, which serve the simple
purpose of giving strength to very delicate membranes." (See Quart.
Journ. Microsc. Sci. for 1862, p. 122.) This verdict, though diversely-
expressed, does not importantly differ from my own judgment given
above.
80
EVENINGS AT THE MICROSCOPE.
marked "with longitudinal lines, very minute and close,
but they mostly bear a central band, and sometimes a
marginal one on each side, of spots set in sinuous lines
like the bands on a mackerel's back ; these are probably
composed of pigment-granules.
These from the pretty Six-spot Burnet Hawk-moth, are
nearly opaque, especially those from the red parts of the
wings, which have a rich ruddy glow by transmitted light-
They are narrow in shape, tapering gradually forward from
the foot-stalk, and terminate mostly in two blunt points.
The ribs are coarse for the size of the scales, and the de-
pressed spaces are marked with irregular pigment grains.
The hairs with which the bodies of Moths are invested
are essentially of the same character as the scales which
clothe their wings. Here are examples from the glowing-
sides of the abdomen of that richly coloured insect, the
Cream-spot Tiger-moth (Arctia villica).
You see they are simple scales, drawn
out to an inordinate length and great
tenuity; each has its quill-like foot-
stalk, and we may trace on some of
them the ribs and transverse dotting,
while here we see all intermediate
stages between the slenderest hair and
the broadly ovate, bluntly pointed,
scales from the wings.
You are familiar of course with the
brilliant little Blue Butterfly (Polyom-
matus Alexis), which dances and glit-
ters in the sunshine on waste places in
June. Among the scales of ordinary
form which clothe the lovely little
wings will occur one here and there of
battledore scale of a different shape from the rest. Here
POLYOMAS ALEXXS. ^ ^^ ^ ^ . ft ^ ^^ jg^^gg
than the average; the foot-stalk is very long, and the shape
INSECTS : WINGS AND THEIR APPENDAGES.
81
of the entire scale is that of a battledore. The ribs are
rather few and coarse, and they have this peculiarity, that
each rib swells at intervals into rounded dilations, each
of which has a minute black point in its centre. In some
of these battledore scales there is, near the lower part
of the expansion, a crescent of minute pigment-grains.
The silvery grey surface of the front wings of a common
moth, known as the Buff-tip {Pygcera bucepltala), is com-
posed of scales of unusual magnitude, and of a remarkable
form, their shape being that of an expanded fan, and being
quite distinguishable by the unassisted eye. The ribs are
very fine and numerous, and there are diverging lines of
pigment-grains running through the scale.
Those of the Emperor Moth (Saticmia pavonia minor)
are likewise triangular in outline, and are remarkable for
being deeply notched at the end ; so deeply as to leave
projecting points (from two to five) as long as, or even
longer than, the undivided portions of the scale.
In some species we find scales the
tips of which are furnished with a curi-
ous sort of fringe. This slide presents
several such in the midst of many of a
more ordinary shape and appearance.
The scales in question are straight, and
parallel-sided, rather narrow, with the
basal end rounded, and the terminal ex_
tremity tapered abruptly to a point ; it
is on each slope of this point that the
fringe is arranged. The surface does
not appear to be elevated in ribs, but
smooth ; while the whole interior, except
a crescent around the foot-stalk, is filled
with pigment-grains, imparting a mottled
appearance. It is remarkable that all
the scales of this form have the foot-
stalk turned in under the expanse. The example which
G
FKIKGKD SCALB OF
PIEBIS.
82 EVENINGS AT THE MICROSCOPE.
we are considering is from the white portion of the wing
of Pieris Glaucippe, sl fine butterfly from China ; but a
similar structure is found in our own Garden Whites and
Meadow Browns (Piericlce and Satyridw).
Scales taken from the brilliant changeable blue-o-reen
patch in the hind-wing of Papilio Paris, a fine Indian but-
terfly, have an interesting appearance. They are simply
pear-shaped in outline, with few longitudinal ribs set far
apart, and numerous strongly marked corrugations running
across between them. That these are really elevations of the
surface, is well seen in some scales, even with transmitted
light, and a high power; for the slopes of the wrinkles
that face the light display the lustrous emerald reflection
proper to the wing, while the transmitted colour of the
whole scale is a rich transparent red.
The dimensions of the scales do not bear any certain
proportion to the size of the insect which is clothed with
them ; those from the broad wings of the noble Satnrnia
Atlas, for example, eight or nine inches in expanse, being
exceeded in size by some from those of our little native
Muslin Moth, an inch wide.
You will say that what I am about to show you is a
lovely object ; but for its right display I must use a low
magnifying power, — not higher than a hundred diameters,
— with condensed light falling upon the surface. It is a
small fragment cut from the wing of Papilio Paris, show-
ing several rows of the scales in their natural arrangement.
The gem-like radiance of the glittering green scales on the
black ones, by which they are environed, glares out with a
splendid effect ; and, what is more interesting, you can
trace the manner in which they are set, — those of each
row slightly overlapping the bases of another row, like
slates on a roof, — and also the mode in which they are in-
serted. The clear horn-coloured membrane of the wing is
seen raised in shallow transverse steps (if I may use such
a term), so that if it were divided longitudinally, the edge
INSECTS I WINGS AND THEIR APPENDAGES.
S3
would appear cut into saw-like teeth. Along the margins
of these ridges are set minute sockets, which are very
distinctly seen, where the scales have been displaced; in
these the tiny foot-stalks of the scales are inserted.
The little Beetles with which we are familiar under the
name of Weevils, characterised by their long slender
snouts, at the end of which they carry curiously folding
antenna?, and which constitute the family C urcidionidce,
are in many cases clothed with scales, to which they owe
their colours and patterns. Several of our native species
display a green or silvery lustre, which under the micro-
scope is seen to be produced by oval scales. But these
are eclipsed by the splendour of many tropical species ;
especially that well-known one from South America,
which is called the Diamond Beetle, and scientifically
Entimus imperialism from its unparalleled magnificence.
A piece of one of the wing-cases of this beetle is gum-
med to the slide now upon the stage. We look at it by
reflected light with a magnifying power of 130 diameters.
We see a black ground, on which is strewn a profusion of
what look like precious stones blazing in the most gorgeous
lustre. Topazes,
sapphires, ame-
thysts, rubies, eme-
ralds, seem sown
broadcast; and yet
not wholly without
regularity, for there
are broad bands of
the deep black sur-
face, where there
and,
are no gems ;
though at consider-
SCALES OF DIAHOXD-BEETLE.
able diversity of
angle, they do all point with more or less precision in
one direction, viz., that of the bands.
G
9
84: EVENINGS AT THE MICROSCOPE.
These gems are flat transparent scales, very regularly
oval in form, for one end is rather more pointed than the
other; there is no appearance of a foot-stalk, and by what
means they adhere, I know not ; they are evidently
attached in some manner by the smaller extremity to the
velvety black surface of the wing-case. The gorgeous
colours seem dependent in some measure on the reflection
of light from their polished surface, and to vary according
to the angle at which it is reflected. Green, yellow, and
orange hues predominate ; crimson, violet, and blue are
rare, except upon the long and narrow scales that border
the junctions of the wing-cases, where these colours are
the chief reflected. Yet there appears to be some positive
colour in their substance ; for in these latter scales, which,
projecting beyond the edge of the wing-case, can be
examined as transparent objects, and that with a high
power, the transmitted light is richly coloured with the
same tints as the same scales displayed under the
Lieberkuhn.
We may derive pleasant instruction from continuing
our observations on a few other wings of insects. If you
have ever thought on the subject, you have probably
taken for granted that the various sounds produced by
insects are voices uttered by their mouths. But it is
not so. No insect has anything approaching to a voice.
Vocal sounds are produced by the emission of air from
the lungs, variously modified by the organs of the mouth.
But no insect breathes through its mouth ; no air is
expelled thence in a single species ; it is a biting, or
piercing, or sucking organ; an organ for the taking of
food, or an organ for olfence or defence; but never an
organ of sound.
The wings are in most cases the immediate causes of
insect sounds; and, in the case of the Two-winged Flies
(Dipt era), Kirby seems to have shown on sufficient evidence
that the humming is produced by the friction of the root or
INSECTS : WINGS AND THEIR APPENDAGES. 85
base of the wings against the sides of the cavity in which
they are inserted. *
There is a pretty little beetle (Clytus), not uncommon
in summer in gardens, remarkable for the brilliant gam-
boge-yellow lines across its dark wing-cases, which makes
a curious squeaking sound when you take it in hand. You
think it is crying; but if you carefully examine it with a
lens while the noise is uttered, you will perceive that
the cause is the grating of the thorax against the front
part of the two wing-cases. Several other beetles produce
similar sounds when alarmed, by rubbing the other end
of the wing-sheaths with the tip of the abdomen. Many
of those genera which feed on ordure and carrion do this.
But the noisiest of all insects are those of the classes
Orthoptera and Ilomoptera, the Crickets and Grass-
hoppers, and the Treehoppers. And these shall bring us
back to our microscope, to which we shall return with
the more zest, after this little interval of repose for our
strained eyes.
Listen ! we hear, coming up the kitchen stairs, the
chirping of the House-cricket (Acheta domestica).
We will catch one for investigation.
Kow, you see, each of the upper wings (or wing-cases)
has a clear space near the centre, of a triangular form,
crossed by one or two slender nervures. This space has
received the name of the tympanum or drum. It is
bounded externally by a broad dark nervure, which with
a low power we see is scored with three or four longitu-
dinal furrows, of course separated by as many horny
ridges. In front of the clear drum, and forming a curved
base to the triangle, a horny ridge passes across, tapering
outwards, which is roughened throughout its length by
close-set teeth exactly like a file. When the insect chooses
to be musical, it partially opens and then closes its wing-
* " Introd. to Entom." ; Lett. xxiv. See, however, the quotation
from Burmeister on p. 91, infra.
S6 EVENINGS AT THE MICROSCOPE.
cases, causing the two files to rub across each other; and
this gives rise to the peculiar ringing vibration, the
intensity of which is heightened by the tense " drum "
acting as a sounding-board.
So at least some say ; but M. Goureau, who has pub-
lished some elaborate observations on the chirping of
insects,* asserts that the sound is chiefly owing to the
action of the "file" (which he calls the "bow") on the
longitudinally ridged nervure, which he calls the "treble-
string."
We see in this individual that is so obliging as to pro-
duce its chirping before us, that he elevates the wing-
sheaths so as to form an acute angle with the body, and
then rubs them together with a very brisk horizontal
motion ; but which of the nervures it is that actually
produces the sounds, it would require a very careful and
elaborate series of experimental researches to determine.
It has been asserted that the legs play a part in the
music by being rubbed against the bows ; this, however,
seems improbable from their relative position.
In the Southern United States, I have had opportuni-
ties of seeing and of hearing a very noisy performer of the
Gryllus tribe, called the Katedid (Pteropliylla concava),
which sings throughout the night in the foliage of the
trees. The sounds, reiterated on every side, resemble a
score or two of quarrelsome people with shrill voices, di-
vided into pairs, the individuals of each pair squabbling
with each other ; " I did ! " " You didn't ! " "I did ! "
" You didn't !" the objurgation maintained with the most
amusing pertinacity, and without a moment's intermission.
Here the wing-sheaths, which are large and as it were
inflated, are certainly the organs of sound. A portion of
each is turned, at right angles to the remainder, over the
back, so that the one partly overlaps the other. The
musical organ consists of a hard glassy ridge in front,
* " Ann. Soc. Ent. de France."
INSECTS : WINGS AND THEIR APPENDAGES. 87
oehind which is a transparent membrane, which appears
tightly stretched over a semicircular rim, like the parch-
ment of a drum, answering in structure and in function
to the part so compared in the Cricket.
This Gryllus I found would chirp freely, when held in
my fingers, provided I held it by the head or thorax, so
as not to interfere with the freedom of the wing-cases :
though these needed only to be partially opened, the
bases being merely slightly separated without affecting
the general contiguity. The two glassy ridges were
rubbed across each other, making the sharp crick. Ordi-
narily this was done thrice, three distinct but rapid cross-
ings making the sound represented by the word " Katedid ; "
but occasionally the insect gave but a single impulse,
uttering as it were but one syllable of the word.
The Locusts and Grasshoppers, however, do, it appears,
make use of their hind legs in producing their chirp. If
you look at this Grasshopper's leg, you will see that the
thigh is marked with a number of transverse overlapping
angular plates, and that the shank carries a series of
short horny points along each side. The insect, when it
chirps, brings the shank up to its thigh, and rubs both to
and fro against the wing-sheaths, doing this by turns with
the right and left legs, which causes the regular breaks
in the sound. The drum, on which this rubbing vibrates,
has been described by the anatomist, De Geer : — "On each
side of the first segment of the abdomen," says he, " im-
mediately above the origin of the posterior thighs, there is
a considerable and deep aperture of rather an oval form,
Avhich is partly closed by an irregular flat plate or oper-
culum of a hard substance, but covered by a wrinkled
flexible membrane. The opening left by this operculum is
semilunar, and at the bottom of the cavity is a white
pellicle of considerable tension, and shining like a little
mirror. On that side of the aperture which is towards the
head there is a little oval hole, into which the point of a
88 EVENINGS AT THE MICROSCOPE.
pin may be introduced without resistance. When the
pellicle is removed, a large cavity appears. In my opinion
this aperture, cavity, and above all the membrane in
tension, contribute much to produce and augment the
sound emitted by the Grasshopper." *
In this case we may without hesitation conclude that
the friction of the thigh-plates and shank-points on the
rough-edges of the wing-cases, produces the musical vibra-
tion on the tense membrane, as rubbing a wet glass with
the finger will yield a loud musical note.
The most elaborate contrivance for the production of
sounds among the Insect races, however, is found among
the Cicada?, celebrated in classical poetry as the very im-
personations of song and eloquence. I regret I cannot
show you this apparatus ; for though we have a British
species, — lately discovered in the New Forest, — it is very
rare. Should you travel, however, either in the old or
new world, you will have abundant opportunities of using
your microscope to verify the following description by
our prince of entomologists, Mr. Kirby : —
" If you look at the under side of the body of a male,
the first thing that will strike you is a pair of large plates
of an irregular form — in some semi-oval, in others trian-
gular, in others again a segment of a circle of greater or
less diameter, covering part of the belly, and fixed to
the trunk between the abdomen and the hind legs. These
are the drum-covers or opercula, from beneath which
the sound issues. At the base of the posterior legs, just
above each operculum, there is a small pointed triangular
process, the object of which, as Reaumur supposes, is to
prevent them from being too much elevated. When an
operculum is removed, beneath it you will find on the ex-
terior side a hollow cavity, with a mouth somewhat linear,
which seems to open into the interior of the abdomen :
next to this, on the inner side, is another large cavity
* De Geer, ii. 471.
INSECTS : WINGS AND THEIR APPENDAGES. 89
of an irregular shape, the bottom of which is divided into
three portions; of these the posterior is lined obliquely
with a beautiful membrane, which is very tense — in some-
species semi-opaque, and in others transparent — and
reflects all the colours of the rainbow. This mirror is
not the real organ of sound, but is supposed to modu-
late it. The middle portion is occupied by a plate of
a horny substance, placed horizontally, and forming
the bottom of the cavity. On its inner side this plate
terminates in a carina or elevated ridge, common to both
drums. Between the plate and the after-breast (post-
])ectus) another membrane, folded transversely, fills an
oblique, oblong, or semilunar cavity. In some species I
have seen this membrane in tension; probably the insect
can stretch or relax it at its pleasure. But even all this
apparatus is insufficient to produce the sound of these
animals; one still more important and curious yet remains
to be described. This organ can only be discovered by
dissection. A portion of the first and second segments
being removed from the side of the back of the abdomen
which answers to the drums, two bundles of muscles meet-
ing each other in an acute angle, attached to a place oppo-
site to the point of the macro of the first ventral segment
of the abdomen will appear. In Reaumur's specimens,
these bundles of muscles seem to have been cylindrical ;
but in one I dissected {Cicada Capensis) they were
tubiform, the end to which the true drum is attached
being dilated. These bundles consist of a prodigious
number of muscular fibres applied to each other, but
easily separable. Whilst Reaumur was examining one of
these, pulling it from its place with a pin, he let it go
again, and immediately, though the animal had been
long dead, the usual sound was emitted. On each side
of the drum-cavities, when the opercula are removed,
another cavity of a lunulate shape, opening into the
interior of the abdomen, is observable. In this is the
90 EVENINGS AT TIIE MICROSCOPE.
true drum, the principal organ of sound, and its aper-
ture is to the Cicada what our larynx is to us. If these
creatures are unable themselves to modulate their sounds,
here are parts enough to do it for them : for the mirrors,
the membranes, and the central portions, with their
cavities, all assist in it. In the cavity last described, if
you remove the lateral part of the first dorsal segment
of the abdomen, you will discover a semi-opaque and
nearly semicircular concavo-convex membrane with
transverse folds; this is the drum. Each bundle of
muscles, before mentioned, is terminated by a tendinous
plate, nearly circular, from which issue several little
tendons that, forming a thread, pass through an aper-
ture in the horny piece that supports the drum, and are
attached to its under or concave surface. Thus the
bundle of muscles, being alternately and briskly relaxed
and contracted, will by its play draw in and let out the
drum: so that its convex surface being thus rendered
concave when pulled in, when let out a sound will be
produced by the effort to recover its convexity; which,
striking upon the mirror and other membranes before it
escapes from under the operculum, will be modulated and
augmented by them. Probably the muscular bundles are
extended and contracted by the alternate approach and
recession of the trunk and abdomen.
" And now, my friend," adds the excellent author,
" what adorable wisdom, what consummate art and skill
are displayed in the admirable contrivance and complex
structure of this wonderful, this unparalleled apparatus !
The great Creator has placed in these insects an organ
for producing and emitting sounds, which in the intricacy
of its construction seems to resemble that which He has
given to man and the larger animals for receiving them.
Here is a cochlea, a meatus, and, as it should seem, more
than one tympanum ! " *
* " Intr. to Ent." ; Lett. xxiv.
insects: wings and their appendages. 91
In some instances the sounds of insects more nearly
approach the character of true voices ; at least so far as
they are produced by the emission of air from the breath-
ing organs, yet not by means of the mouth. One of the
most eminent of living entomologists, Dr. Burmeister,
tells us so. Finding that the buzz of a large fly (Eristalis
tenax) still continued after the winglets, the poisers, and
even the wings, had been quite cut off except their stumps
(only in this last case the sound was somewhat weaker
and higher), he conceived that the spiracles, or breathing
holes, lying between the meso- and meta-thorax must be
the instruments of the sound; which, accordingly, he
found to cease entirely when they were stopped with
gum, though while the wings were in vibration. Pur-
suing his researches, he extracted one of these spiracles,
and opening it carefully, found its posterior and inner
lip, which is directed towards the commencement of the
trachea, to be expanded into a small, flat, crescent-shaped
plate, upon which are nine parallel, very delicate, horny
lamina3, the central one being the largest, while those on
each side become gradually smaller and lower; so it is,
he is persuaded, in consequence of the air being forcibly
driven out of the trachea and touching these lamince,
that they are made to vibrate and sound, precisely in
the same way as with the glottis of the larynx. Dr.
Burmeister (who remarks that Chabrier, in his Essai sur
le Vol cles Insectes, p. 45, etc., has also explained the
hum of insects as produced by the air streaming from
the thorax during flight, and also speaks of lamina;,
which lie at the aperture of the spiracles), in order to
be certain that the lamina? in question in the posterior
spiracles of the thorax are alone concerned in producing
sound, also inspected the anterior ones, but without find-
ing in them any trace of these lamime. He explains
the weaker and sharper tones produced when the wings,
all but the very roots, are cut off, as resulting from the
92 EVENINGS AT THE MICROSCOPE.
weaker vibrations of the contracting muscles, and con-
sequently less forcible expulsion of the air when the
vibratory organs are removed ; and he thinks, with
Chabrier, that some air may escape through the open
trachece of the wings which are cut off. Though he
regards these lamina? as the cause of humming in bees
and flies, he does not decide that other causes may not
produce the buzz of cockchafers, etc., in the thoracic
spiracles of which he could not discern them.*
* a
Man. of Entom.,"46S.
INSECTS : THEIR BREATHING ORGANS. 93
CHAPTER VI.
INSECTS : THEIR BREATHING ORGANS.
In order to understand the passage last quoted from
Burmeister, you ought to know something of the manner in
which breathing is performed among insects. Essentially,
breathing is the same function, wherever it occurs ; and
it does occur, doubtless, in all animals under some form
or other. It is the absorption of oxygen from without to
the fluids within, to repair the waste constantly produced
by vital energy. But it may be obtained from different
sources, and imbibed in various modes.
All insects in the perfect state are air-breathers; that
is, they procure their oxygen from the air as we do ; and
most of them are such in their earlier stages. Even in
exceptional cases, viz., those larvaa or pupae which are
provided with what represent gills, and appear to be
dependent on the water for their respiration, the excep-
tion is rather apparent than real, for the function is still
performed in air-vessels. Now these air-vessels shall
afford us some interesting microscopical observations.
This brown fly, which is buzzing and hovering on in-
visible wings over the flowers in the garden, you perhaps
take for a bee. No; it has but two wings; for I have
caught it, and you may ascertain the fact for yourself;
it belongs to the genus Syrphus. Having caught it, I
deprive it of life by means of the very organs I am going
to examine, for I turn a tumbler over it and insert under
the ed^e a lighted lucifer-match. In a few seconds it is
dead — suffocated; for phosphoric and sulphuric acids
94 EVENINGS AT THE MICROSCOPE.
introduced into the breathing tubes quickly destroy life.
I presently take it out, and, putting it into a dissecting-
trough under a lens, cut up the abdomen with a pair of
fine-pointed scissors. Then I pin open the divided
abdomen to the bottom of the trough, which is coated
with wax for the purpose; and, looking at it with the
lens — but you shall look for yourself.
Well, you see little else but the polished brown walls of
the body and a number of fine white threads. It is those
threads that we want. With a small camel's-hair pencil
I move them to and fro in the water, and soon perceive
that they are like little trees with comparatively thick
trunks, sending off many branches, which gradually be-
come exceedingly slender. Here and there short thick
branches break out on two opposite sides, and on each
side are connected with the wall of the abdomen. Here
then with the fine scissors I snip them across, and lift up
a portion with the hair pencil into a drop of water which
J have already put into the live box. The cover now
flattens the drop, spreads the white threads, — and the
object is ready for our eye.
We have before us a considerable portion of the tra-
cheal system of the fly. And though, owing to the com-
plication of the parts, and the injury our rude anatomy
has done, we cannot trace the beautiful regularity which
exists in life, we may see the principle on which they are
arranged, and much of the perfection with which they
are constructed.
Here then is a system of pipes, some large, some
small ; the smaller branching forth from the large, and
themselves sending off yet smaller branches, which in their
turn divide and subdivide until the final ramifications are
excessively attenuated. Besides these, we see here and
there ovate or barrel-shaped reservoirs, having the same
appearance and intimate structure as the pipes, but of
much larger calibre and connected with them by a branch.
INSECTS : THEIR BREATHING ORGANS.
95
This, I say, is the breathing system, or a large portion
of it. These pipes receive the air from without through
trap-doors which we will examine presently, and convey
it to the most distant parts of the body. In ourselves
the air is inhaled into a great central reservoir — the
lungs ; and the blood dispersed through every part is
brought to this reservoir to be oxygenated. In insects
it is the blood that is collected into a great central
reservoir, and the air is distributed by a minutely
divided system of vessels over the blood-reservoir.
The trachece or air-pipes have a silvery white appear-
WS^W)
AIE-PIPE OF FLY.
ance by reflected light ; but if we use transmitted light
and put on a high power, we discern a wonderful
structure, which I will describe in the eloquent language
of Professor Rymer Jones, and you shall estimate its
truth as you examine the object : —
" There is one elegant arrangement connected with the
breathing-tubes of an insect specially worthy of admira-
tion; and perhaps in the whole range of animal mechanics
it would be difficult to point out an example of more
exquisite mechanism, whether we consider the object of
the contrivance or the remarkable beauty of the structure
96 EVENINGS AT THE MICROSCOPE.
employed. The air-tubes themselves are necessarily ex-
tremely thin and delicate; so that on the slightest pres-
sure their sides would inevitably collapse, and thus com-
pletely put a stop to the passage of air through them,
producing, of course, the speedy suffocation of the insect,
thad not some means been adopted to keep them always
permeable; and yet, to do so, and at the same time to
preserve their softness and perfect flexibility, might seem
a problem not easily solved. The plan adopted, however,
fully combines both these requisites. Between the two
thin layers of membrane which form the walls of every
air-tube, a delicate elastic thread (a wire of exquisite
tenuity) has been interposed, which, winding round and
round in close spirals, forms by its revolutions a cylindri-
cal pipe of sufficient firmness to preserve the air-vessels
in a permeable condition, whilst at the same time it does
not at all interfere with its flexibility; this fine coil is
continued through every division of the trachece, even
to their most minute ramifications, a character whereby
these vessels are readily distinguishable when examined
under the microscope."*
Man has imitated this exquisite contrivance in the
spiral wire-spring which lines flexible gas-pipes; but his
wire does not pass between two coats of membrane. One
of the most interesting points of the contrivance is the
way in which the branches are (so to speak) inserted
in the trunk, the two wires uniting without leaving a
blank. It is difficult to describe how this is done; but
by tracing home one of the ramifications you may see
that it is performed most accurately; the circumvo-
lutions of the trunk-wire being crowded and bent round
above and below the insertion (like the grain of timber
.-around a knot), and the lowest turns of the branch- wire
*being enlarged so as to fill up the opening entirely.
* "Nat. Hist, of Anim./'i. 6.
INSECTS : TIIEIR BREATHING ORGANS. 97
You must not suppose, however, that the whole of one
tube is formed out of a single wire. Just as, in a piece of
human wire-work, the structure is made out of a certain
number of pieces of limited length, and joinings or inter-
lacings occur where new lengths are introduced, so,
strange to say, it seems to be here. It is strange, I say,
that it should be so, when there can be no limit to the
resources, either of material, or skill to use it ; but so it
is, as you may see in this specimen, which has been dis-
sected out of the body of a silkworm. The spiral is
much looser here than in the air-tube of the fly, the turns
of the wire being wider apart; and hence its structure is
much more easily traced. Here you see, in many places,
the introduction of a new wire, always beginning with
the most fine-drawn point, but presently taking its place
with the rest so as to be undistinguishable from them.
In some cases certainly (perhaps this may be the expla-
nation of the phenomenon in all) the wire so introduced
may be found to terminate with the; like attenuation
before it has made a single turn, and seems to be inserted
when the permanent curvature of the pipe would leave
the wires on the outer side of the curve too far apart,
half a turn, or even much less, then being inserted of
supernumerary wire.
I told you that the air enters these tubes through
certain "trap-doors." This is not the term which the
physiologist employs, certainly : he calls them spiracles.
In our own bodies the air enters only at one spiracle,
a curiously defended orifice opening just in front of the
gullet, at the back of the mouth. But in the class of
animals we are now considering there are a good many
such breathing orifices. You may see them to great
advantage in any large caterpillar, the silkworm for
example, where all along the sides of the pearl-grey body
you perceive a row of dots, which with a lens you dis-
cover to be little oval disks sunken into little pits, of
H
D8
EVENINGS AT THE MICROSCOPE.
a black hue with a white centre, through which is a very
slender slit. There are nine of these organs on each side,
a pair to each segment or division of the body, with the
exception of the first, which is the head, and of the
third and fourth, which are destined to bear the wings ;
these are destitute of spiracles.
Essentially, these organs, under whatever modifications
of form and position they may appear, have the same
structure. They are narrow orifices, each with two lips
capable of being opened at the will of the animal, or
accurately closed ; and in many soft-skinned insects, such
as the silkworm and most larvae, they are set in a horny
ring ; by which means they are prevented from collapsing
through the unresisting character of the general integu-
ment. The opening and shutting of them is performed by
an internal apparatus of muscles, which is sometimes
strengthened by being attached to two horny plates,
which project inwardly.
But the most curious thing
to be noted in the structure
of these spiracles is the con-
trivance which induced me
to call them trap - doors.
Small as are their openings,
they are still large enough
to admit many floating par-
ticles of dust, soot, and
other extraneous matters,
which would tend to cloa:
up the delicate air-passages,
and to impede the right
performance of their im-
portant functions. Hence
they need to be
SriBACLE OF FLY.
guarded
with some sort of sieve, or
filter, which, while admitting the air, shall exclude the dust-
INSECTS : THEIR BREATHING ORGANS.
99
Various and beautiful are the modes in which this
common purpose is effected, but I can show you only two
or three. This is one of the breathing orifices of the
common House-fly, in which, as you see, minute processes
grow from the margin all round, which extend partly
across the open area, branching and ramifying again and
again, and spreading and interlacing with those of the
opposite side, so as to form a perfect sieve, which the
linest atoms of dust cannot penetrate.
The same end is attained, in another way, in the dirty
cylindrical grub, which is found so abundantly at the roots
of grass in pasture lands, and which country folk call,
from the toughness of its skin, "leather-coat." It is the
larva of the Crane-fly (Tipula oleracea), so familiar to us
under the sobriquet of Daddy Long-legs. I can easily
procure one of these, for, unfortunately, they are but too
common. Here is one, who shall have the honour of being
martyred for the benefit of science. Before we assassinate
him, however, just look here at the hinder extremity of his
body, where there is a space,
surrounded and protected by
several points, and in this
space, two black spots.
With the dissecting-scissors
I have carefully cut out one
of these specks, and now I put
it for illumination on the stage
of the microscope. There is,
first of all, a dark horny ring
of an oval figure, a little way
within which there is an
opaque dark plate of the same
figure, but smaller, occupying
the central portion of the area,
margin of the plate and the bounding ring is occupied
by a series of slender filaments, placed side by side,
ii 2
SPIRACLE OF LEATHEU-COAT.
The space between the
100
EVENINGS AT THE MICROSCOPE,
proceeding from one to the other, through the interstices
of which the air is filtered. The central plate seems to
be quite imperforate.
The fat, thick-bodied grubs of those beetles called
chafers exhibit, in their spiracles, a modification of this
structure, rendered still more elaborate. In the case of
the larva of the common
Cockchafer (Melolontlta vul-
garis), for example, the cen-
tral plate is a projection
from one side of the margin
of the spiracle ; or, to use a
geographical simile, we may
say that, instead of being
an island in the midst of a
lake, it is a promontory.
Thus the breathing space
is a crescent-shaped band,
which is crossed in every
part by bars passing from
the margin to the projecting plate. But, as if the inter-
stices left by these bars would be too coarse for the pur-
pose, they are made still finer by a membrane, which is
stretched across them, and which is pierced with a number
of exceedingly minute round holes, through which alone
the air is admitted.
In many of the two-winged flies, which inhabit the
water in their earlier stages, there are some interesting
contrivances and modifications connected with the organs
of respiration. It is necessary that the orifices of the
air-tubes should be brought at intervals to the surface of
the water, in order to come into contact with the external
air; while, at the same time, it is important that as small
a portion as possible of the animal's body be exposed to
danger, by being protruded from its sheltering element.
An example in point you may see in this vase.
Wll""
SPIBACLE OF COCKCHAFER-GBUB.
INSECTS : THEIR BRFATIIIXG ORGANS. 101
Here is a slender worm, an inch and a half in length,
thickest a little behind the head, and tapering gradually to
a lengthened tail, the twelve divisions of the body being
very conspicuous. It swims up and down, or to and fro,
in the clear water, with a not very rapid, wriggling move-
ment, throwing its body alternately from side to side in
the form of the letter S.
This is the maggot of a handsome dipterous fly, some-
times called the Chameleon-fly (Stratiomys chamceleon).
There is much about it to reward observation and careful
examination with a low magnifying power, especially the
head, with its pointed snout, and its pair of foot-like
palpi, or feelers. These are situated one on each side of
the head, are three-jointed, the last joint being studded
with short stiff spines, and the second having a thumb-
like projection. With these organs, the grub roots and
burrows among the decaying vegetable matter at the
bottom for its food ; and when not so engaged, they are
often rapidly vibrated in a singular manner, the sight of
which might induce a feeling of fear, as if they were
threatening weapons of offence — a pair of poisonous
stings, for instance ; they have, however, no such func-
tion, the poor grub being perfectly harmless.
What I wish you chiefly to observe, however, is the
tail, with its curious organisation. With the naked eye,
you can perceive that the last joint is much slenderer
and more lengthened than the rest, and that it is tipped
with a beautiful crown of feathers, like the diadem of
some semi-savage prince. This is best seen when the
animal comes to the surface, which it always does tail
uppermost ; for, as soon as the tip reaches the air, the
plumes instantly open, and form an exquisite cone or
funnel, from which every drop of moisture is excluded,
though the water stands around at the level of the brim.
A few seconds it remains motionless thus, the whole body
hanging downwards, suspended from the caudal coronet :
102
EVENINGS AT THE MICROSCOPE.
then, sudden])', the tips of the plumes curve inward toward
each other, inclosing a globule of air; and the animal
wriggles away into the depths, carrying its burden, like a
pearl, or a glittering bubble of quicksilver, behind it.
This you may observe with the unassisted sight ; and
you may mark also, how, from time to time, a portion,
more or less, of the bubble of gleaming air is inhaled or
expired by the animal, causing a diminution or increase
of its volume ; and this of itself would convince you that
it is the spiracles of the animal which are thus pro-
tected.
The application of a
low magnifying power,
say from thirty-five to
fifty diameters, — for we
can hardly use a higher
power than this to the
animal while alive, —
will reveal a few more
of the details.
We see, then, that the
extremity of the last seg-
ment forms a circular
disk, hollowed in the
centre, where it is per-
forated with the two
orifices of the air-pipes.
The margin of this disk
carries about thirty stiff
but slender spines or
bristles, some of which
are branched in a forked
manner. Each bristle
bears, on its two oppo-
site sides — viz. , on those
aspects which face the next bristle on either hand — two
GBVB OF CHAMELEON-FLY.
insects: their breathing organs. 103
series of not very close-set branchlets, set like the plumes
of a feather, or the pinnae of a fern-leaf, which give it
the elegant plumose appearance which the unassisted eye
recognises. The bristles have a granulose surface near
the extremity, and terminate in fine points.
The curious faculty of repelling water, which the in-
terior surface of this plumy coronet possesses, is of the
highest value in the economy of the insect ; for, on the
one hand, it permits the breathing orifice to be brought
into contact with the air, even when nearly a quarter of
an inch below the surface ; and, on the other hand, it
allows the volume of air inclosed within the funnel to
be perfectly isolated, and carried securely away, as a
reservoir for the wants of the animal, when engaged in
its avocations of necessity or pleasure, in the recesses of
its sub-aquatic groves. It is remarkable that so com-
plete is this repellent power, that when the tail is at the
surface the animal may make a very perceptible descent
without breaking the continuity of the air, the surface
presenting the curious phenomenon of a deep funnel-
shaped dimple leading down to the tail.
The chameleon-fly is not, however, so abundant and so
universally distributed as that you may always calculate
upon being able to repeat these observations when you
will. I shall, therefore, show you an analogous example,
much more easily obtained. Both are inhabitants of our
fresh waters : the chameleon-grub lives in ponds, crawling
among the stems of aquatic plants, and occasionally visit-
ing the surface in the manner you have seen ; but it is
uncertain^; in some seasons not uncommon, in others,
scarcely to be met with by the most persevering search.
For my next specimen, I have but to go with a basin to the
water-butt in the yard, and take a dip of the surface-water
at random : I shall be pretty sure of a score at least.
Here they are swarming, as I told yon. What, those
tilings'? why, they are gnat-grubs. Well, don't despise
104 EVENINGS AT THE MICROSCOPE.
them, you will find tliem worth looking at. I dare say
you have never submitted them to half an hour's micro-
scopical examination. I have caught one with a spoon,
and put it into this narrow glass trough of water, that it
may rest conveniently on the stage.
We will take a cursory glance at its entire person.
Here is a flat, roundish head, a great globose, swollen
thorax, and a long, slender, many-jointed body, ending in
a curious fork. But all is curious : — the head, with its
horny transparency ; its pair of rod-like antennae, covered
with minute points ; its two black eye-patches ; and its
jaws, beset with strong, curved hairs, set in radiating
rows, and, ever and anon, working to and fro with the
most rapid vibrations : the thorax, — so transparent, with
its amber-like clearness, that you can discern the dorsal
vessel, which contains the blood, ever dilating and col-
lapsing with the most beautiful regularity ; and, beneath
this, the gullet, through which, now and then, descends a
dark pellet of food, to join the mass already lodged in
the stomach farther down, — a result, by the way, that
explains that incessant vibration and pumping motion of
the mouth-organs, which thus evidently are engaged in
collecting food from the water ; though, even with this
power, we can see no solid matter taken in, till we dis-
cern it agglomerated in the swallowed pellets: the body,
or abdomen, with its ten joints, all (with a slight excep-
tion) the counterparts of each other ; and each carrying
its own dilatation of the dorsal vessel, and its own portion
of the long and well-filled intestinal canal. All these,
I say, are very interesting and curious to observe ; espe-
cially when we select, as I have done, a young individual
for examination ; since the tissues then possess a trans-
lucency which is essential to our seeing with distinct-
ness anything of the internal organization, but which
soon gives place to opacity, as the insect advances
in age.
INSECTS : THEIR BREATHING ORGANS. 105
Very curious, too, are the hairs with which the whole
surface of the animal is furnished at certain definite
points. But these are seen to more advantage in an
older specimen; for, in this one of tender hours, they are
nearly simple ; whereas, in an opaque, nearly full-grown
individual, every hair is seen to be studded with second-
ary points, that project from its surface throughout its
length. These hairs are arranged in beautiful radiating
pencils or tufts, and scattered, as I have said, at definite
points over the whole body : — there is a tuft on each
antenna ; one on the forehead ; one in front of each eye-
spot ; several circles of them set round the thorax ; one
circle of scanty pencils set round each segment of the
body, and a few smaller tufts scattered about besides; all
of them springing from minute round warts.
The extremity of the abdomen deserves, however, a
separate investigation, and we will now direct our atten-
tion to the tail-end of our tiny grub. There are ten
segments to the abdomen; at the eighth it seems to
divide into two branches, one longer than the other.
This appearance, however, is due to the circumstance that
the respiratory tube is sent forth from the eighth segment,
and that the ninth and tenth segments are bent away at
an angle from the general line of the body.
The ninth segment is very small : the tenth is squarish,
with rounded corners, and is brought to a thin edge.
Around the margin there is the most exquisite array of
hairs possible ; at one corner there are three pencils ;
while round the opposite, and down the corresponding side
run, in two rows, twelve pencils, set very close to each
other, and each containing a large number of very slender
hairs. The extreme end of the segment is ornamented
with four diverging organs of taper conical form and
crystalline clearness, through the midst of each of which
passes a very fine branch of the air-tube system, which
gives off still more attenuated branchlets in its course.
10G EVENINGS AT THE MICROSCOPE.
We have not yet, however, examined the origin of this
air-breathing system. There is but one entrance to the
air, or rather two placed close together, at the end of
that round column, which is sent off from the eighth
segment of the abdomen. This column, which is rough-
ened all over with minute points, and fringed with rows of
hairs, ends in a horny, conical point, which seems entire
while under water, but no sooner does it come to the sur-
face, than it is seen to split into five triangular pieces,
which open widely, and expose a hollow, at the bottom of
which are the two spiracles.
From these the two main air-pipes are seen to com-
mence, and to proceed along the centre of the column,
thence into the abdomen, which they traverse, one along
each side, sending off slender branchlets all along, and
becoming more and more attenuated themselves ; till, at
length, we trace them into the thorax, and thence through
the slender neck into the head itself, until they terminate
in fine points close to the back of the mouth. It needs,
it is true, a very transparent specimen to follow the
tracheal tubes thus through their entire course ; but in
such it can be clone without difficulty. And it is very
instructive to do so ; inasmuch as one such personal
examination of an insect, under a good microscope, will
make you far more familiar with the peculiarities of its
physiology than the clearest book- descriptions, or even
the best and most elaborate plates, alone.
Perhaps you may think I have kept you too long over
these gnat-grubs ; but my reason for being more minute
in the examination of this creature is, that its extreme
abundance in every place, and through the greatest part
of the year, puts it in the power of every one to procure
a specimen alive and healthy almost whenever he chooses ;
and, therefore, it is peculiarly available for microscopic
study : while the transparency of its tissues, and its gene-
rally simple organization, make it a more than usually
INSECTS : THEIR BREATHING ORGANS. 107
suitable object for investigation : besides which, there
are the beautiful and interesting points in the details of
its structure, which I have been endeavouring to bring
before you.
Not less interesting and remarkable is the change in
the position of the spiracles, which takes place as soon as
this grub arrives at the pupa or chrysalis state. The skin
of the active, fish-like larva splits down the back, and out
presses an equally active little monster; which, if you did
not know it, you would never think of connecting with the
grub from which it has proceeded; so totally different is
it in form, in structure, and in motions.
We shall easily find some in our basin that have passed
into this stage. Yes, here is one, which will please to
take its place in the glass trough with its younger brothers.
How strange the transformation ! It reminds us of a
lobster, though, of course, the resemblance is only appa-
rent. With the naked eye we see that the thorax is
greatly enlarged, not only actually, but proportionally ;
that it forms an oval mass, occupying some five-sixths, at
least, of the entire animal ; the rest, apparently, being
taken up by a slender, many-jointed abdomen, which
curves round the great thorax, and, bending under it,
ends in a very delicate, transparent swimming-plate. It
is this curving abdomen, with its terminal swimmer, and
its backward strokes in swimming, that constitute the
resemblance to a prawn or lobster.
If we now bring a low power with reflected light to bear
on it, we shall see the progress the animal has made in
this its change of raiment. The thorax shows on its
sides the future wings, crumpled and folded down, the
nervures of which we can discern distinctly. The elegant
little head, too, can be well made out ; its eyes now per-
fectly marked with the numerous six-sided facets that
belong to the matured organs of vision in these creatures;
its antenna?, like slender rods, folded down side by side
108 EVENINGS AT THE MICROSCOPE.
along the inferior edge of the thorax ; the short palpi
lying outside these ; and within, both the lancets and
piercers that are destined to subserve the blood-sucking
propensities of our sanguinary little subject, when it
attains its winged condition ; — all encased in the trans-
parent pupa-skin, that lies like a loose wrapper around
everything.
The extremity of the abdomen has now nothing to do
with respiration, and hence it is never brought to the
surface of the water, as it was constantly before. The
little animal still habitually lives in contact with the air,
coming up to it with rapid, impatient jerks, whenever it
has descended ; but it is invariably the summit of the
thorax that is uppermost, and when the creature rests, it
is this part that touches the surface.
Why is this 1 you ask. Look, and you will see why.
From the summit of the thorax project two little horns,
which, under the microscope, are seen to be clear trum-
pet-shaped tubes with open mouths, cut as it were
obliquely off. These enter the thorax close to the bases
of the wings ; and w-hen we confine the animal in a glass
cell, exercising a gentle pressure upon the thorax, we see
bubbles of air alternately projected from the trumpet
mouths of the tubes and sucked in again. These, then,
are the spiracles, the orifices of the air-tubes, where the
vital fluid enters the body, and whence it is carried to
every part of the system.
There is something curiously beautiful about the struc-
ture of these spiracular tubes, of which I cannot attempt
to explain the object. With a high magnifying power,
their whole exterior surface is seen to be covered witli
regular rounded scales, overlapping each other, an 1 very
closely resembling those of a fish.
INSECTS : THEIR FEET. 101)
CHAPTER VII.
insects: their feet.
I have here inclosed a small window-fly in the live-box of
the microscope, that you may examine the structure of its
feet as it presses them against the glass cover ; and thus
not only get a glimpse of an exquisitely formed structure,
but acquire some correct ideas on the question of how a
fly is enabled to defy all the laws of physics, and to walk
jauntily about on the under surface of polished bodies,
such as glass, without falling, or apparently the fear of
falling. And a personal examination is the more desirable
because of the hasty and erroneous notions that have been
promulgated on the matter, and that are constantly dis-
seminated by a herd of popular compilers, who profess to
teach science by gathering up and retailing the opinions
of others, often without the slightest knowledge whether
what they are reporting is true or false.
The customary explanation has been that given by
Derham in his "Physico-theology"; that " divers flies and
other insects, besides their sharp-hooked nails, have also
skinny palms to their feet, to enable them to stick to glass,
and other smooth bodies, by means of the pressure of the
atmosphere, after the manner as I have seen boys carry
heavy stones, with only a wet piece of leather clapped on
the top of a stone." Bingley, citing this opinion, adds
that they are able easily to overcome the pressure of the
air " in warm weather, when they are brisk and alert ;
but towards the end of the year this resistance becomes
too mighty for their diminished strength; and we see flies
110 EVENINGS AT TOE MICROSCOPE.
labouring along, and lugging their feet on windows as if
they stuck fast to the glass : and it is with the utmost
difficulty they can draw one foot after another, and dis-
engage their hollow cups from the slippery surface." *
But long ago another solution was proposed : for Hooke,
one of the earliest of microscopic observers, described the
two palms, pattens, or soles (as he calls the indvUl%), as
"beset underneath with small bristles or tenters, like the
Avire teeth of a card for working wool, which, having a
contrary direction to the claws, and both pulling different
Avays, if there be any irregularity or yielding in the surface
of a body, enable the fly to suspend itself very firmly."
He supposed that the most perfectly polished glass pre-
sented such irregularities, and that it was moreover
always covered with a " smoky tarnish," into which the
hairs of the foot penetrated.
The " smoky tarnish," is altogether gratuitous ; and
Mr. BlackAvall has exploded the idea of atmospheric pres-
sure, for he found that flies could Avalk up the interior of
the exhausted receiver of an air-pump. He had explained
their ability to climb up A'ertical polished bodies by the
mechanical action of the minute hairs of the inferior sur-
face of the palms; but further experiments haATing shown
him that flies cannot Avalk up glass Avhich is made moist
by breathing on it, or which is thinly coated with oil or
flour, he was led to the conclusion that these hairs are in
fact tubular, and excrete a viscid fluid, by means of which
they adhere to dry polished surfaces ; and on close insjDec-
tion with an adequate magnifying power, he was always
able to discover traces of this adhesive material on the
track on glass both of flies and various other insects
furnished with pul-cUli, and of those spiders which
possess a similar faculty, f
In the earlier editions of Kirby and Spence's " Intro-
duction to Entomology," Mr. Kirby had adopted the
* " Anim. Biogr." t "L:nn. Trans.," xvi. 490, 768.
insects: their feet. Ill
suctorial hypothesis. But in a late one he made an
allusion to Mr. Blackwall's opinion, and added the follow-
ing interesting note : —
" On repeating Mr. Blackwall's experiments, I found,
just as he states, that when a pane of glass of a window
was slightly moistened by breathing on it, or dusted with
flour, bluebottle-flies, the common house-flies, and the
common bee-fly (Eristalis tenax), all slipped down again
the instant they attempted to walk up these portions of the
glass j and I moreover remarked that, each time, after
thus slipping down, they immediately began to rub first
the two fore tarsi and then the two hind tarsi together, as
flies are so often seen to do, and continued this operation
for some moments before they attempted again to walk.
This last fact struck me very forcibly, as appearing to
give an importance to these habitual procedures of flies,
that has not hitherto, as far as I am aware, been attached
to them. These movements I had always regarded as
meant to remove any particle of dust from the legs, but
simply as an affair of instinctive cleanliness, like that of
the cat when she licks herself, and not as serving any
more important object; and such entomological friends as
I have had an opportunity of consulting tell me that their
view of the matter was precisely the same ; nor does Mr.
Blackwall appear to have seen it in a different light, since,
though so strongly bearing on his explanation of the wxay
in which flies mount smooth vertical surfaces, he never at
all refers to it. Yet, from the absolute necessity which the
Hies on which I experimented appeared to feel, of cleaning
their indvilli immediately after being wetted or clogged
with flour, however frequently this occurred, there cer-
tainly seems ground for supposing that their usual and
frequent operation for effecting this, by rubbing their tarsi
together, is by no means one of mere cleanliness or amuse-
ment, but a very important part of their economy, essen-
tially necessary for keeping their pulvilli in a fit state for
112 EVENINGS AT THE MICROSCOPE.
climbing up smooth vertical substances by constantly re-
moving from them all moisture, and still more all dust,
which they are perpetually liable to collect. In this
operation the two fore and two hind tarsi are respectively
rubbed together for their whole length ; whence it might
be inferred that the intention is to remove impurities from
the entire tarsi ; but this I am persuaded is not usually
the object, which is simply that of cleaning the under
side of the pulvilli, by rubbing them backward and for-
ward along the whole surface of the hairs with which the
tarsi are clothed, and which seem intended to serve as a
brush for this particular purpose. Sometimes, indeed,
when the hairs of the tarsi are filled with dust throughout,
the operation of rubbing them together is intended to
cleanse these hairs ; because, without these brushes were
themselves clean, they could not act upon the hairs of the
under side of the pulvilli. Of this I witnessed an inter-
esting instance in an Eristalis tenax, which, by walking
on a surface dusted with flour, had the hairs of the whole
length of the tarsi, as well as the pulvilli, thus clogged
with it. After slipping down from the painted surface of
the window-frame which she in vain attempted to climb,
she seemed sensible that before the pulvilli could be
brushed, it was requisite that the brushes themselves
should be clean, and full two minutes were employed to
make them so, by stretching out her trunk, and passing
them repeatedly along its sides, apparently for the sake of
moistening the flour and causing its grains to adhere ; for
after this operation, on rubbing her tarsi together, which
she next proceeded to do, I saw distinct little pellets of
flour fall clown. A process almost exactly similar I have
always seen used by bluebottle-flies and common house-
flies, which had their tarsi clogged with flour by walking-
over it, or by having it dusted over them ; but these
manoeuvres are required for an especial purpose j and on
ordinary occasions, as before observed, the object in
insects: their feet. 113
rubbing the tarsi together is not to clean them,, but the
pidvilli, for which they serve as brushes. Besides rubbing
the tarsi together, flies are often seen, while thus em-
ployed, to pass the two fore tarsi and the tibia?, with
sudden jerks, over the back of the head and eyes, and
the two hind tarsi and tibia? over and under the wings,
and especially over their outer margins, and occasionally
also over the back of the abdomen. That one object of
these operations is to clean these parts from dust, I have
no doubt, as on powdering the flies with flour they thus
employ themselves, sometimes for ten minutes, in detach-
ing every part of it from their eyes, wings, and abdomen ;
but I am also inclined to believe that, in general, when
this passing of the legs over the back of the head and
outer margin of the wings takes place in connexion with
the ordinary rubbing of the tarsi together, as it usually
does, the object is rather for the purpose of completing
the entire cleansing of the tarsal brushes (for which the
row of strong hairs visible under a lens on the exterior
margin of the wings seems well adapted), so that they
may act more perfectly on the pulvillL Here, too, it
should be noticed, in proof of the importance of all the
pulvilli being kept clean, that as the tarsi of the two
middle legs cannot be applied to each other, flies are
constantly in the habit of rubbing one of these tarsi and
its pidvillus, sometimes between the two fore tarsi, and
at other times between the two hind ones
" Though the above observations, hastily made on the
spur of the occasion since beginning this note, seem to
prove that it is necessary the pulvilli of flies and of some
other insects should be kept free from moisture and dust
to enable them to ascend vertical polished surfaces, they
cannot be considered as wholly settling the question as to
the precise way in which these pidvilli, and those of in-
sects generally, act in effecting a similar mode of progres-
sion ; and my main reason for here giving these slight
I
114 EVENINGS AT THE MICROSCOPE.
hints is the hope of directing the attention of entomo-
logical and microscopical observers to a field evidently,
as yet, so imperfectly explored.
" After writing the above, intended as a conclusion of
this note, I witnessed to-day (July 11, 1842) a fact which
I cannot forbear adding to it. Observing a house-fly on
the window, whose motions seemed very strange, I ap-
proached it, and found that it was making violent con-
tortions, as though every leg were affected with St. Vitus's
dance, in order to pull its jmlvilli from the surface of the
glass, to which they adhered so strongly that though it
could drag them a little way, or sometimes by a violent
effort get first one and then another detached, yet the
moment they were placed on the glass again they adhered
as if their under side were smeared with bird-lime. Once
it succeeded in dragging off* its two fore-legs, when it
immediately began to rub the pulvilli against the tarsal
brushes; but on replacing them on the glass they adhered
as closely as before, and it was only by efforts almost con-
vulsive, and which seemed to threaten to pull off its limbs
from its body, that it could succeed in moving a quarter
of an inch at a time. After watching it with much interest
for five minutes, it at last by its continued exertions got its
feet released and flew away, and alighted on a curtain, on
which it walked quite briskly, but soon again flew back
to the window, where it had precisely the same difficulty
in pulling its pulvilli from the glass as before; but after
observing it some time, and at last trying to catch it, that
I might examine its feet with a lens, it seemed by a
vigorous effort to regain its powers, and ran quite actively
on the glass, and then flying away I lost sight of it. I am
unable to give any satisfactory solution of this singular
fact. The season, and the fly's final activity, preclude
the idea of its arising from cold or debility, to which
Mr. White attributes the dragging of flies' legs at the
close of autumn. The pulvilli certainly had much more
IKSECTS : THEIR FEET. 115
the appearance of adhering to the glass by a viscid material
than by any pressure of the atmosphere ; and it is so far
in favour of Mr. Black wall's hypothesis, on which one
might conjecture that from some cause (perhaps of disease)
the hairs of the pul villi had poured out a greater quantity
of this viscid material than usual, and more than the
muscular strength of the fly was able to cope with."*
In the foot of the fly under our own observation, you
may see how well the joints of the tarsus are covered
with hairs, or rather stiff pointed spines, of various di-
mensions and distances apart, and hence how suitable these
are for acting the part of combs to cleanse the palms. But
these last are the organs that most claim and deserve our
examination. In the specimen of the little Musca that
I have imprisoned, the last tarsal joint is terminated by
two strong divergent hooks which are themselves well,
clothed with spines, and by two membranous flaps or
palms beneath them. These are nearly oval in outline,
though in some species they are nearly square, or triangular,
and in some of a very irregular shape. They are thin,
membranous, and transparent, and when a strong light
is reflected through them, we see their structure under
this power of GOO diameters very distinctly.
The inferior surface of the palm, on which we are now
looking, is divided into a vast number of lozenge-shaped
areas, which appear to be scales overlapping each other,
or they may be divided merely by depressed lines. From,
the centre of each area proceeds a very slender, soft, and.
flexible pellucid filament, which reaches downwards to the
surface on which the fly is walking, and is there slightly
hooked, and enlarged into a minute fleshy bulb. Those
from the areas near and at the margins of the palms more
and more arch outwards, so that the space covered by
the bulbs of the filaments is considerably greater than
that of the palm itself.
* " In trod, to Entom.," 7th Ed., 458.
i 2
116
EVENINGS AT THE MICROSCOPE.
Now it is evident that the bulbous extremities of these
soft filaments are the organs of adhesion. We notice how
they drag and hold, as the fly draws its foot from its
place ; and it seems almost certain that the adhesion is
effected by means of a glutinous secretion poured out in
minute quantities from these fleshy tips. When the foot
is suddenly removed, we may often see a number of tiny
particles of fluid left on the glass where the filaments had
been in contact with it : but I do not build conclusively
on this appearance, because the fly, having been confined
for some quarter of an hour in this nearly tight glass cell,
has doubtless exhaled some moisture, which has condensed
on the glass ; and the specks we see may possibly be due
to the filaments of the palms having become wet by re-
peatedly brushing the moist
surface. Mr. Hepworth, how-
ever, asserts that a fluid is
poured out from these fila-
ments, and is deposited on
the glass, when the fly is vi-
gorous, with great regularity.
He says that " when in a
partially dormant state, the
insect does not appear to be
able to give out this secretion,
though it can still attach it-
self : indeed, this fluid is not
essential for that purpose." *
It is asserted that the speckled
pattern of fluid left on the
glass by the fly's footsteps re-
mains (if breathed on) when
the moisture is evaporated ;
and hence it is presumed to be of an oily nature.
In some Beetles the joints of the foot are furnished with
* " Micros. Journal" for April, 1854.
FOOT OF FLT.
insects: their feet. 117
similar appendages. I shall now show you the fore-foot
of a well-known insect, called by children the Bloody-nose
Beetle (Timarcha tenebricosa), a heavy-bodied fellow, of a
blue-black colour, abundant in spring and summer on
hedge-banks. You have doubtless often observed it, and
have been amused, perhaps, at seeing the drop of clear
scarlet fluid which exudes from its mouth when touched.
The feet in this species are broad and well developed.
You may see with the naked eye, on turning it up, that
its dilated joints are covered on the under surface with a
velvety cushion of a rusty -brown colour; and here, under
a low power of the microscope with the Lieberkiihn, you
can determine the nature of the velvet.
The foot, or tarsus, as it is technically called, is com-
posed of four very distinct pieces ; of which the first is
semicircular, the second crescent-shaped, the third heart-
shaped, and the fourth nearly oval. The last is rounded
on all sides, has no cushioned sole, and carries two stout
hooks. The first three are flat, or even hollowed beneath
into soles, something like the hoof of a horse ; and the
whole interior bristles with close-set minute points, the
tips of which terminate at the same level, and form a
velvety surface. Now, these points are the whitish bulbous
extremities exactly answerable to those on the palms of
the fly, and doubtless they answer the very same purpose.
Only here they are set in far closer array, and are a
hundred times more numerous; whence we may reason-
ably presume a higher power of adhesion to be possessed
by the beetle. The structure is best seen in the male,
which may be distinguished by its smaller dimensions,
and by its broader feet.
A still better example of a sucking foot is this of the
Dyticus marginalis. It is the great flat oval beetle, which
i-< fond of coming up to the surface of ponds, and hanging
there by the tail with its pair of hind legs stuck out on
each side at right angles ; the redoubtable monster which
118
EVENINGS AT THE MICROSCOPE.
little boys who bathe hold in such salutary awe under the
name of Toe-biter. We have turned the tables upon the
warrior, and have bitten his toe — off, and here it is.
This is the tarsus of one of the fore limbs.
The peculiarity that first strikes us is that the first
three joints are as it were fused into one, and spread out
so as to make a large roundish plate. The under surface
of this broad plate is covered with a remarkable array of
FOOT OF WATER-BEETLE.
Large Sucker, bb. Two smaller suckars.
c. Small crowded suckers.
2. Oue of the last more
enlarged.
sucking-disks, of which one is very large, occupying about
a fourth part of the whole area. It is circular, and its
face is strongly marked with numerous fibres radiating
from the centre. jSTear this you perceive two others of
similar form and structure, but not more than one-tenth
insects: their feet. 119
part of its size ; one of these, moreover, is smaller than
the other. Indeed, the size and number of these organs
differ in different individuals of the same species.
The greater number of the suckers are comparatively
minute ; but they are proportionally multitudinous and
crowded. Each consists of a club-shaped shaft, with a
circular disk of radiating fibres attached to its end.
The whole apparatus constitutes a very effective instru-
ment of adhesion.
There is a somewhat similar dilatation of the first joints
of the tarsus, but for a very different object, in the Honey-
bee; and it is particularly worthy to be observed, not only
for the interesting part which it plays in the economy
of the insect, but for the example it affords us of the
adaptation of one and the same organ to widely different
uses, by a slight modification of its structure.
It is the hind foot of the Bee that wTe are now to ex-
amine. The first joint is, as you see, enlarged into a wide,
long, and somewhat ovate form, constituting a flattish
plate, slightly convex on both surfaces. The upper face
presents nothing remarkable ; but the under side is set
with about nine stiff combs, the teeth of which are horny
straight spines, set in close array, and arranged in trans-
verse rows across the joint, nearly on a level with its
plane, but a little projecting, and so ordered that the tips
of one comb slightly overlap the bases of the next. We
see them in this example very distinct, because their
colour, a clear reddish-brown, contrasts with a multitude
of tiny globules of a pale yellow hue, like minute eggs,
which are entangled in the combs.
Now these globules serve to illustrate the object of this
apparatus. They are grains of pollen ; the dust that is
discharged from the anthers of flowers, which, being
kneaded up with honey, forms the food of the maggot of
the Bee, and is, therefore, collected with great persever-
ance by the industrious insect : and the way in which it
120 EVENINGS AT THE MICROSCOPE.
collects it is, by raking or combing it from the anthers,
by means of these effective instruments on its hind feet.
You see that in this specimen the combs are loaded
with the grains, which lie thickly in the furrows between
one comb and another. But how do they discharge their
gatherings 1 Do they return to the hive as soon as they
have accumulated a quantity such as this, which one
would suppose they could gather in two or three scrapes
of the foot 1 No ; they carry a pair of panniers, or col-
lecting baskets, which they gradually fill from the combs,
and then return to deposit the results of their collecting
One of these baskets I can show you; and, indeed, it
would be unpardonable to overlook it, for it is the com
panion structure to the former. I make the stage forceps
to revolve on its axis, and thus bring into focus the joint
(tibia) immediately above that of the combs, and so that
we shall look at its opposite surface: that is, the outer.
We notice at once two or three peculiarities, which
distinguish the joint in this instance from other parts of
the same limb, and from the corresponding part in the
same limb of other insects.
First, the surface is decidedly concave, whereas it is
ordinarily convex. Secondly, this concave surface is
smooth and polished (except that it is covered with a
minute network of crossed lines), not a single hair, even
the most minute, can be discerned in any part; whereas
the corresponding surface of the next joints, both above
and below, is studded with fine hairs, as is the exterior
of insects generally. Thirdly, the edges of this hollowed
basin are beset with long, slender, acute spines, which
follow the same curve as the bottom and sides, expand-
ing widely, and arching upward.
Here, then, we have a capital collecting basket. Its
concavity of course fits it to contain the pollen. Then
its freedom from hairs is important: hairs would be out
of place in the concavity. Thirdly, the marginal spines
insects: their feet. 121
greatly increase the capacity of the vessel to receive the
load, on the principle of the sloping stakes which the-
farmer plants along the sides of his waggon when he is
going to carry a load of hay or corn.
But, you ask, how can the Bee manage to transfer the
pollen from the combs to the basket 1 Can she bend up
the tarsus to the tibia 1 or, if she could, surely she could
reach only the inner, not the outer surface of the latter.
How is this managed 1
A very shrewd question. Truth to say, the basket
you have been looking at never received a single grain
from the combs of the joint below it. But the Bee has
a pair of baskets and a pair of comb-joints. It is the
right set of combs that fills the left basket, and vice versa.
She can easily cross her hind-legs, and thus bring the
tarsus of one into contact with the tibia of the other ;
and if you will pay a moment's more attention to the
matter, you will discover, in this beautiful series of con-
trivances, some further points of interest still. If you
look at this living Bee, you notice that, from the position
of the joints, when the insect would bring one hind-foot
across to the other, the under surface of the tarsus
would naturally scrape the edge of the opposite tibia in
a direction from the basis of the combs towards their
tips; and, further, that the edge of the tibia so scraped
would be the hinder edge, as the leg is ordinarily carried
in the act of walking.
Now, if you take another glance at the basket-joint in
the forceps of the microscope, you will see — what, perhaps,
you have already noticed — that the marginal spines have
not exactly the same curvature on the two opposite edges,
but that those of the one edge are nearly straight, or at
most but slightly bowed, whereas those of the opposite
edge are strongly curved, the arc in many of them
reaching even to a semicircle ; so that their points,
after performing the outward arch, return to a posi-
122 EVENINGS AT THE MICROSCOPE.
tion perpendicularly over the medial line of the
basket.
It is the outer or hinder edge of the joint that carries the
comparatively straight spines. These receive the grains
from the combs, which, then falling into the basket, are
received into the wide concavity formed partly by its
bottom and sides, but principally by the arching sjnnes
of the opposite edge. Their curving form would have been
less suitable than the straighter one to pass through the
interstices of the combs, because it would be much more
difficult to get at their points; while, on the other hand,
the straight lines of these would have been far less
effective as a receiver of the burden. The thickness of
the spines is just that which enables them to pass freely
through the interstices of the comb-teeth, and no more.
On the whole, this combination of contrivances reads
us as instructive a lesson on the wisdom of God displayed
in creation as any that we have had brought under our
observation.
The end to be attained by all this apparatus is worthy
of the wondrous skill displayed in its contrivance; for it
is connected with the feeding of the stock ; and whatever
diminishes the labour of the individual bees, enables a
larger number to be supported. But, valuable as is the
Honey-bee to man, there are other important purposes to
be accomplished, which are more or less dependent,
collaterally, on this series of contrivances.
" In many instances it is only by the bees travelling
from flower to flower that the pollen and farina is carried
from the male to the female flowers, without which they
could not fructify. One species of bee would not be
sufficient to fructify all the various sorts of flowers, were
the bees of that species ever so numerous ; for it requires
species of different sizes and different constructions. M .
Sprengel found that not only are insects indispensable
in fructifying different species of Iris, but some of them,
INSECTS : THEIR FEET. 123
as /. Xiphium, require the agency of the larger humble-
bees, which alone are strong enough to force their way
beneath the style-flag ; and hence, as these insects are
not so common as many others, this Iris is often barren,
or bears imperfect seeds." *
The legs and feet of Caterpillars are constructed on
a very different plan from those of perfect insects, as
you may see in this living Silkworm. The first three
segments of the body, reckoning from the head, are
furnished each with a pair of short curved limbs set close
together on the under side. These represent the true
legs of the future moth, and show, notwithstanding
their shortness, four distinct joints, of which the last is
a little pointed horny claw. The whole limb resembles
a short stout hook. Then two segments occur which
are quite smooth beneath, and destitute of limbs; and
then on the sixth we begin to find another series, which
goes on regularly, a pair on each segment, to the eleventh
and final one, with the single exception of the tenth
segment, which is again deprived of limbs.
But these organs are of a very peculiar character.
They have no representatives in the mature insect, but
disappear with the larva state; and they are not con-
sidered limbs-proper at all, but merely accessory develop-
ments of the skin to serve a special purpose. They are
sometimes called claspers, sometimes false-legs, but more
commonly pro-legs.
Each consists of a fleshy wart, which is capable to
some extent of being turned inside out, like the finger
of a glove. Partly around the blunt and truncate
extremity are set two rows of minute hooks, occupying
the side next the middle line of the caterpillar in a
semicircle alon^ the mannn. These hooks arch outward
* Penny Cyclop., art. Bee. The researches of the late Mr. Darwin
and others have shown that the agency of insects in the fertilization
of plants is very far more important than had been suspected.
124 EVENINGS AT THE MICROSCOPE.
as regards the axis of the pro-leg, though the majority
of them point towards the medial line of the body.
The double row is somewhat interrupted at its middle
point ; and just there, in each pro-leg, a clear vesicle or
fleshy bladder protrudes from the sole, which may
perhaps serve as a very delicate organ of touch, or may
exude a viscid secretion helpful to progress on smooth
bodies. The hooks seem adapted to catch and hold the
fine threads of silk, which most caterpillars spin as a
carpet for their steps.
In some cases the circle of hooks is complete, as in
this example, which I find in one of the slides of my
drawer, marked "Pro-leg of a Caterpillar." It is some
large species, probably a Sphinx, for the hooks are very
large, of a clear orange-brown hue, and set in a long
oval ring — single as to their basis, but double as to their
points — completely around the extremity of the foot.
These hooks belong only to the skin, as may be well seen
in this prepared specimen, doubtless mounted in Canada
balsam; — for their roots are mere blunt points, set but
little below the surface of the thin skin, without any
enlargement or apparent bulb.
insects: stings and ovipositors. 125
CHAPTER VIII.
INSECTS : STINGS and ovipositors.
Probably at some period of your life you have been stung
by a bee or wasp. I shall take it for granted that you
have, and that, having tasted the potency of these war-
like insects' weapons with one sense, you have a curiosity
to examine them with another. The microscope shall aid
your vision to investigate the morbific implement.
This is the sting of the Honey-bee, which I have but
this moment extracted. It consists of a dark brown
horny sheath, bulbous at the base, but suddenly diminish-
ing, and then tapering to a fine point. This sheath is
split entirely along the inferior edge, and by pressure with
a needle I have been enabled to project the two lancets,
which commonly lie within the sheath. These are two
slender filaments of the like brown horny substance, of
which the centre is tubular, and carries a fluid, in which
bubbles are visible. The extremity of each displays a
beautiful mechanism, for it is thinned away into two thin
blade-edges, of which one remains keen and knife-like,
while the opposite edge is cut into several saw-teeth
pointing backwards.
The lancets do not appear to be united with the
sheath in any part, but simply to lie in its groove ; their
basal portions pass out into the body behind the sheath,
where you see a number of muscle-bands crowded around
them : these, acting in various directions, and being in-
serted into the lancets at various points, exercise a com-
plete control over their movements, projecting orretracting
126 EVENINGS AT THE MICROSCOPE.
them at their will. But each lancet has a singular pro-
jection from its back, which appears to act in some way
as a guide to its motion, probably preventing it from
slipping aside when darted forth, for the bulbous part of
the sheath, in which these projections work, seems formed
expressly to receive them.
Thus we see an apparatus beautifully contrived to
enter the flesh of an enemy : the two lancets finely
pointed, sharp-edged, and saw-toothed, adapted for
piercing, cutting, and tearing ; the reversed direction
of the teeth gives the weapon a hold in the flesh, and
prevents it from being readily drawn out. Here is an
elaborate store of power for darting them forth, in the
numerous muscle-bands ; here is a provision made for the
precision of the aim ; and, finally, here is a polished sheath
for the reception of the weapons and their preservation
when not in actual use. All this is perfect; but something
still was wanting to render the weapons effective, and
that something your experience has proved to be supplied.
The mere insertion of these points, incomparably finer
and sharper than the finest needle that was ever polished
in a Sheffield workshop, would produce no sensible result
on our feelings ; and most surely would not be followed
by the distressing agony attendant on the sting of a bee.
We must look for something more than we have seen.
We need not be long in finding it. For here, at the
base of the sheath, into which it enters by a narrow neck,
lies a transparent pear-shaped bag, its surface covered all
over, but especially towards the neck, with small glands
set transversely. It is rounded behind, where it is entered
by a very long and slender membranous tube, which,
after many turns and windings, gradually thickening
and becoming more evidently glandular, terminates in
a blind end.
This is the apparatus for preparing and ejecting a
powerful poison. The glandular end of the slender tube
INSECTS : STINGS AND OVIPOSITORS.
12:
is the secreting organ : here the venom is prepared ; the
remainder of the tube is
a duct for conveying it to
thebag, a reservoir in which
it is stored for the moment
of use. By means of the
neck it is thrown into the
groove at the moment the
sting is projected; thesame
muscles, probably, that dart
forward the weapon com-
pressing thepoison-bag, and
causing it to pour forth its
contents into the groove,
whence it passes on be-
tween the two lancets into
the wound which they have
made.*
A modification of this ap-
paratus is found through-
out a very extensive order
of Insects, — the Hymeno-
ptera ; but in the majority
of cases it is not connected
with purposes of warfare.
Wherever it occurs it is
always confined to the
female sex, or (as in the
case of some social insects)
to the neuters, which are un-
developed females. When
it is not accompanied by a
poison-reservoir it is used
* Some further researches of value on the stings of Wasps and Bees,
with copious illustrations, will be found in Hardwicke's Science-Gossip
for 1868, p. 148, by Dr. Mills, p. 205, by " S. &," and for 1873, p. 132,
by Mr. Nisbett Browne.
STING OF BEE.
a. Tip of Lancet, more enlarged.
128 EVENINGS AT THE MICROSCOPE.
for the deposition of the eggs, and is hence called an
ovipositor ■, though in many cases it performs a part much
more extensive than the mere placing of the ova.
In the large tribe of Cuckoo-flies (Ichneumonidce) which
spend their egg- and larva-states in the living bodies of
other insects, this ovipositor is often of great length; even
many times longer than the rest of their bodies ; for the
larvae which have to be pierced by it require to be reached
at the bottom of deep holes, and other recesses, in whicli
the providence of the parent had placed them for security.
The structure of the organ may be seen in this little
species, not more than one-sixth of an inch in entire
length, of which the ovipositor projects about a line.
Under the microscope you see that this projection con-
sists of two black fleshy filaments, rounded without and
flattened on their inner faces, which are placed together,
and of the true implement for boring, in the form of a
perfectly straight awl, of a clear amber hue, very slender,
and brought to an abrupt oblique point, where there are
a few exceedingly fine reverted teeth. It is probably
double, though it refuses to open under the pressure
which I bring to bear upon it. At the base are seen
Avithin the semi-pellucid abdomen the slender horns, on
which the muscles act in projecting the borer.
You are doubtless aware that the little berries which
GALL-FLY, AND MECHANISM OF OVIPOSITOR.
look like bunches of green currants, often seen growing on
insects: stings and ovipositors. 129
the oak, are not the proper fruit of the tree, but diseased
developments produced by a tiny insect, for the protec-
tion and support of her young. Kirby and Spence tell
us that the parent fly introduces her egg into a puncture
made by her curious spiral sting, and in a few hours it
becomes surrounded with a fleshy chamber. Mr. Yirey
says the gall-tubercle is produced by irritation, in the
same way as an inflamed tumour in an animal body, by
the swelling of the cellular tissue, and the flow of liquid
matter, which changes the organisation, and alters the
natural external form.
Perhaps a still more charming example of animal
mechanics is that' furnished to us by the Saw-flies
(Tenthredinidce). These are very common four-winged
insects of rather small size, many species of which are
found in gardens and along hedges in summer, produced
from grubs which are often mistaken for true caterpillars,
as they strip our gooseberry and rose bushes of their
leaves; but which may be distinguished from them by
the number of their pro-legs, and by their singular
postures; for they possess from eight to fourteen pairs
of the former organs, and have the habit of coiling up
the hinder part of their body in a spiral ring, while they
hang on to the leaf by their six true feet.
These saw-fly caterpillars are produced from eggs
which are deposited in grooves made by the parent fly
in the bark of the tree or shrub whose future leaves are
destined to constitute their food ; and it is for the con-
struction of these grooves, and the deposition of the
eggs in them, that the curious mechanism is contrived
which I am now bringing under your notice.
Almost all our acquaintance with this instrument and
the manner of its employment, we owe to the eminent
French naturalist, Reaumur, and to his Italian con-
temporary, Valisnieri. Their details I shall first cite, as
they have been put into an English dress by Kennie, and
K
130 EVENINGS AT THE MICROSCOPE.
then show you a specimen dissected out by myself, and
point out some agreements and some discrepancies be-
tween it and them.
" In order to see the ovipositor, a female saw-fly must
be taken, and her belly gently pressed, when a narrow
slit will be observed to open at some distance from the
anus, and a short, pointed, and somewhat curved body,
of a brown colour and horny substance, will be protruded.
The curved plates which form the sides of the slit are
the termination of the sheath, in which the instrument
lies concealed till it is wanted by the insect.
"The instrument thus brought into view is a very
finely-contrived saw, made of horn, and adapted for
penetrating branches and other parts of plants where the
eggs are to be deposited. The ovipositor-saw of the
insect is much more complicated than any of those
employed by our carpenters. The teeth of our saws are
formed in a line, but in such a manner as to cut in two
lines parallel to and at a small distance from each other.
This is effected by slightly bending the points of the
alternate teeth right and left, so that one half of the
whole teeth stand a little to the right, and the other half
a little to the left. The distance of the two parallel
lines thus formed is called the course of the saw, and it
is only the portion of wood which lies in the course that
is cut into sawdust by the action of the instrument.
It will follow, that in proportion to the thinness of a
saw there will be the less destruction of wood which
may be sawed. When cabinet-makers have to divide
valuable wood into very thin leaves, they accordingly
employ saws with a narrow course ; while sawyers who
cut planks use one with a broad course. The ovipositor-
saw, being extremely fine, does not require the teeth to
diverge much, but from the manner in which they
operate, it is requisite that they should not stand like
those of our saws in a straight line. The greater portion
insects: stings and ovipositors. 131
of the edge of the instrument, on the contrary, is
towards the point somewhat concave, similar to a scythe,
while towards the base it becomes a little convex, the
whole edge being nearly the shape of an italic f.
" The ovipositor-saw of the fly is put in motion in the
same way as a carpenter's hand-saw, supposing the
tendons attached to its base to form the handle, and the
muscles which put it in motion to be the hand of the
carpenter. But the carpenter can only work one saw at
a time, whereas each of these flies is furnished with
two, equal and similar, which it works at the same time
— one being advanced and the other retracted alternately.
The secret, indeed, of working more saws than one at
once is not unknown to our mechanics ; for two or three
are sometimes fixed in the same frame. These, however,
not only all move upwards and downwards simultane-
ously, but cut the wood in different places : while the
two saws of the ovipositor work in the same cut, and,
consequently, though the teeth are extremely fine, the
effect is similar to [that of] a saw with a wide set
[or course].
" It is important, seeing that the ovipositor-saws are
so fine, that they be not bent or separated while in
operation ; and this also nature has provided for by
lodging the backs of the saws in a groove, formed by
two membranous plates, similar to the structure of a
clasp-knife. These plates are thickest at the base,
becoming gradually thinner as they approach the point
which the form of the saw requires. According to
Valisnieri, it is not the only use of this apparatus to
form a back for the saws, he having discovered between
the component membranes two canals, which he sup-
poses are employed to conduct the eggs of the insect
into the grooves which she has hollowed out for them.
" The teeth of a carpenter's saw, it may be remarked,
are simple, whereas the teeth of the ovipositor-saw are
k 2
132 EVENINGS AT THE MICROSCOPE.
themselves denticulated with fine teeth. The latter also
combines at the same time the properties of a saw and
of a rasp or file. So far as we are aware, these two
properties have never been combined in any of the tools
of our carpenters. The rasping part of the ovipositor,
however, is not constructed like our rasps, with short
teeth thickly studded together, but has teeth almost as
long as those of the saw, and placed contiguous to them
on the back of the instrument, resembling in their form
and setting the teeth of a comb. " *
Now look at this object which I have just extracted
from the abdomen of a rather large female Saw-fly, of a
bright green hue spotted with black. The first portion
of the apparatus that protruded on pressure was this
pair of saws of an y^-like figure. These agree in general
with those described ; here is in each the double-curved
blade, the strengthened back, the rasp-like jagging of
the lateral surfaces, the teeth along the edge, and the
secondary toothlets of the latter. All these essential
elements we see, but there is much discrepancy in the
detail, and many points not noticed ; — in part, doubtless,
owing to its being another species which was under
observation, and partly to the inferiority of the micro-
scopes employed a hundred and fifty years ago to those
we are using.
In the first place, the curve of the f is different, the
convexity of the edge being towards the point and the
concavity nearest the base. Then the strengthening does
not appear to me a groove in which the saw plays, but
a thickening of the substance of the back. Each main
tooth of the saw in this case is the central point in the
edge of a square plate, which appears to be slightly con-
cave on its two surfaces, being thickened at its two sides,
at each of which, where it is united to the following plate,
it rises, and forms with it a prominent ridge running trans-
* "Insect Architecture," 153.
INSECTS : STINGS AND OVIPOSITORS.
133
versely to the course of the saw. Each of these ridges then
forms a second tooth, as stout as the main edge-tooth,
which, with the rest of the same series, forms a row of
teeth on the oblique side of the saw, in a very peculiar
manner, difficult to express by words. It is singular that
this side of the saw should be studded with minute hairs,
since those would seem to interfere with the action of
the saw, or at least be liable to be themselves rubbed
down and destroyed in its action. But their existence
is indubitable ; there they are, pointing at a very acute
angle towards the tip of the saw. The back edge of the
implement bristles with many close-set hairs or spines,
forming a sort of brush, but pointing in an opposite
direction.
Each main tooth of the edge-series is cut into one or
two minute toothlets on its posterior side (next the base
OUTER SAW OF SlW-Hl.
a. A portiou more enlarged.
of the saw) and about half-a-dozen on its opposite side
(next the tip). The texture is clear and colourless where
thin ; but in the thickened parts, as the main teeth, the
transverse ridges, and the back, it is a clear amber-
yellow ; the strengthening back-piece deepening to a rich
translucent brown.
There is, however, in this species of mine a second set
of implements, of which the French naturalist, observant
134 EVENINGS AT THE MICROSCOPE.
as he was, takes not the slightest notice ; and his English
commentator appears to have as little suspected its pre-
sence. This pair of saws that we have been looking at is
hut the sheath of a still finer pair of lancets or saws,
which you may see here. These are much more slender
than the former, and are peculiar in their construction
I2TNEB SAW OF SAW-FLY.
Their extreme tip bears only saw-teeth, and these are
directed backwards ; but one side of the entire length
presents a succession of cutting edges, as if a number of
short pieces of knife-blade had been cemented on a rod,
in such a manner as that the cutting edges should be
directed backwards, and overlap each other. The other
lateral surface is plain, and both are convex in their
general aspect. The appearance of these implements is
very beautiful, for the texture is of a clear pale amber ;
but the structure is strengthened by a band which runs
along each edge, and by transverse bands crossing at
regular intervals, of a denser tissue ; and these are of a
rich golden translucent brown.
From the construction of this implement I should infer
that its force is exerted by pulling and not by pushing ;
the direction of the teeth and of the cutting plates shows
this. The sharp horny point is probably thrust a little
way into the solid wood or bark, and then a backward
pull brings the teeth and cutting plates to act upon the
material, and so successively. And probably these points
are the first parts of the whole apparatus that come into
operation j the blunter saws of the sheath serving mainly
INSECTS : STINGS AND OVIPOSITORS. 135
to widen and deepen the course, after the iiner points
have pioneered the way.
The merry little jumping insects called Frog-hoppers
(Tettigonia), one of which in its larva state emits the
little mass of froth so common on shrubs, and called
cuckoo-spit, are furnished with a set of tools for their
own private carpentry, which, though less elaborate than
those of the saw-flies, are worthy of a moment's glance.
If we catch one of these vaulters, and gently press the
abdomen, we shall see proceeding from its hinder and
lower part a thickish piece, large compared with the size
of the insect, which it is then easy to extract with a pair
of fine-pointed pliers. I have just done this, and here
is the result on a slip of glass.
First, there is a pair of brown protecting pieces, oblong
in form, and studded with hairs like the rest of the
exterior of the body. From between them projects what
resembles a lancet, of the usual translucent amber-
coloured horn, appropriated to these instruments (which
is to them what steel is to us) ; and this we shall pre-
sently discover to be composed of two blades exactly
alike, convex without and concave within, applied face
to face. One edge of this pair of implements is quite
smooth, but the other is cut into the most beautifully
regular and most minute teeth.
This, however, is but the sheath. Within the two
spoon-shaped faces there lie two other lancets, blade to
blade, still finer and more delicate. Both edges of these
blades are of the most perfect keenness, without a flaw;
but their sides appear roughened with rows of very
minute horny knobs, like a rasp.
I shall illustrate this demonstration by another extract
from Reaumur, premising, however, that his observations
refer to the large species of true Cicadce from warmer
latitudes, whose machinery seems to differ from that of
our little friends in some particulars. For example, the
136 EVENINGS AT THE MICROSCOPE.
two inner lancets seem to be united in one, in Reaumur's
species, or else, which I think more probable, he did not
succeed in separating them.
He describes the two curved spoon-shaped pieces as
finely indented on both sides with teeth, which are strong,
nine in number, arranged with great symmetry, increas-
ing in fineness towards the point. This instrument he
describes as composed of three pieces, the two exterior,
which he calls the files, and another pointed, which he
compares to a lancet, which is not toothed. "The files
are capable of being moved forward and backward, while
the central one remains stationary ; and as this motion
can be effected by pressing a pin or the blade of a knife
over the muscles on either side at the origin of the
ovipositor, it may be presumed that those muscles are
destined for producing similar movements when the
insect requires them. By means of a finely-pointed pin
carefully introduced between the pieces, and pushed
very gently downwards, they may be, with no great
difficulty, separated in their whole extent.
" The contrivances by which those three pieces are held
united, while at the same time the two files can be easily
put in motion, are similar to some of our own mechanical
inventions, with this difference, that no human workman
could construct an instrument of this description so
small, fine, exquisitely polished, and fitting so exactly.
We should have been apt to form the grooves in the
C9ntral piece, whereas they are scooped out in the
handles of the files, and play upon two projecting ridges
in the central piece, by which means this is rendered
stronger. M. Reaumur discovered that the best manner
of showing the play of this extraordinary instrument is
to cut it off with a pair of scissors near its origin, and
then, taking it between the thumb and the finger at the
point of section, work it gently to put the files in
motion.
IXSECTS : STINGS AND OVIPOSITORS. 137
" Beside the muscles necessary for the movement of
the files, the handle of each is terminated by a curve of
the same hard horny substance as itself; which not only
furnishes the muscles with a sort of lever, but serves to
press, as with a spring, the two files close to the central
piece. *
The use of these instruments is the same as I have
already alluded to in the case of the saw-flies. The
female Tree-hopper deposits her eggs in holes, which she
bores in dead twigs by means of these files and lancets.
The branches chosen are said to be easily known by
being studded with little oblong elevations, caused by
the partial raising of a splinter of wood at the orifice of
the hole, to which it serves as a cover. These are
arranged in a single line ; the holes which they protect
being only half-an-inch in length, and reaching to the
pith, whose course they then follow. Not more than six
or eight eggs are laid in each hole ; but an idea of the
labours of the industrious and provident mother will be
formed from the fact that she lays six or seven hundred
eggs in the course of the summer.
* "Insect Architecture," 149.
138 EVENINGS AT THE MICROSCOPE.
CHAPTER IX.
INSECTS : THEIR MOUTHS.
The parts of the mouth in different Insects afford an
almost endless store of delightful observations ; and the
more as, with all their variety, they are found to be in
every case composed of the same essential elements.
You would not think so, indeed ; you would naturally
suppose — looking at the biting jaws of a Beetle, the
piercing proboscis of a Bug, the long, elegantly-coiled
sucker of a Butterfly, the licking tongue of a Bee, the
cutting lancets of a Horse-fly, and the stinging tube of
a Gnat — that each of these organs was composed on
a plan of its own, and that no common structure could
exist in instruments so diverse. But it is so, as we
shall see.
We may consider the various organs of the mouth
as most harmoniously and perfectly developed in the
active carnivorous Beetles ; the Carahidce, or ground-
beetles, for instance. Let us examine the head of
this black Scarites from the garden ; and first from
above.
In front of the polished head-shield, and jointed to it
by a broad transverse straight edge, is a four-sided piece,
forming an oblong figure, nearly twice as broad as long,
a little convex, and marked with six little pits or sinkings
of the surface, along its front edge. This is the upper
lip; but, instead of being fleshy, as ours is, it is composed
of a hard polished black shelly substance, of a peculiar
insects: their mouths. 139
nature, called cliitine, the same substance as the hard
parts of all Insects and Crustacea are made of.
From beneath the sides of this there project on each
side two broad hooked pieces, which, as you see, I can
with a needle force out laterally, so as to show their form
better, for they hinge upon the sides of the face, beneath
the head-shield. Each forms the half of a crescent, the
curved points of which are turned towards each other, and
can work upon each other, the points crossing like shears.
These are the proper biting jaws, or mandibles, and in
many of the larger beetles they have great power of hold-
ing and crushing. Sometimes their inner side is cut into
strong teeth, but here this side forms a blunt cutting
edge ; the upper surface, however, is scored with ridges
and furrows like a file ; and this structure is best seen
in the left jaw, which, when the pair close, crosses over
the right. This is an action of the jaws the reverse of ours ;
but it is characteristic of all articulate animals, in which
the jaws, whenever present, always work horizontally,
from right to left, and not vertically, up and down.
I will now, by making the forceps revolve, bring the
under side of the head into view ; for, without separating
the parts by dissection (which, however, is by no means
difficult), it is impossible to see them all from one point
of view. The part nearest our eye now is the chin, a wide
horny piece, like the upper lip, jointed to the head by its
straight hind edge, but, unlike it, having its front edge
hollowed out with two deep notches, the central piece
between them itself notched at its tip. Immediately above
this notched central tooth (I speak of the relative position
of the parts, supposing the insect to be crawling on the
ground, without reference to the way in which we turn
it about on the microscope), and united with it, there is a
sort of solid square pedestal, on which stand a pair of
jointed organs, and between them an oblong horny plate
rounded at the tip, where it bears two bristles. This
140
EVENINGS AT THE MICROSCOPE.
latter is the tongue, while the jointed organs on each
side are called feelers, — palpi; though this is a begging
of the question, for we do not really know the function
of these organs. The chin, the tongue (ligula), and these
palpi, constitute together the under lip.
Between the tongue and the biting jaws, or mandibles,
we see a pair of organs similar to these latter, but smaller,
less solid, and more curved. These are the under or
secondary jaws, maxillce, the use of which is to hold the
MOUTH OF BEETLE.
{Seen from beneath.)
a, upper lip ; b, mandibles ; c, maxillae ; d, maxillary palpi ; e, tongue ;
f, labial palpi ; g, chin.
food, while the biting jaws work on it, and to convey it
when masticated to the back of the mouth. Their whole
inner edge is set with short stiff bristles, which towards
the tips of the jaws become spines. Near the bases of
these jaws, on the outer edge, are jointed two other pairs
of palpi, one pair to each jaw ; of which the exterior is
much stouter and longer than the interior. Thus this
INSECTS : THEIR MOUTHS. 141
beetle has three pairs of these many-jointed organs, viz.,
the labial, and the two pairs of maxillary palpi.
Now, in this form of mouth, which has been called a
perfect or complete mouth, — that is, one in which all the
constituent parts can be well made out, we find the fol-
lowing organs : — 1. the upper lip (labrum) ; 2. the man-
dibles; 3. the maxilla?; with o, the maxillary palpi; 4.
the lower lip (labium), comprising /3, the tongue, y, the
labial palpi, c, the chin (mentum).
I now exhibit to you the head of the Honey-bee. The
front is occupied by an upper lip, and a pair of biting
jaws (mandibles), which do not greatly differ from the
same parts in a beetle. The jaws, however, are more
hatchet-shaped, or rather like the hoof of a horse, sup-
posing the soles to be the opposing surfaces. The other
organs are greatly modified, so that you would scarcely
recognise them. The under jaws (maxillce) are greatly
lengthened ; and the two, when placed in contact, form a
kind of imperfect tube or sheath. Within these is the
lower lip, divided into its constituent parts : the thick
opaque chin, at its basal end ; then the two labial palpi,
each consisting of four joints, of which the two terminal
ones are minute, while the two basal are large and
greatly lengthened, so as to resemble in appearance the
maxillce, whose function they imitate also ; for the pair
of palpi when closed form an inner sheath for the tongue.
Finally, you see this organ, which is the most curiously
developed and modified of all, for it is drawn out to a
long slender, cylindrical tube, formed of a multitude of
close-set rings, and covered with fine hairs. Some deny
it to be tubular, and maintain that it is solid ; but cer-
tainly it appears to me to have a distinct cavity through-
out, with thickish walls.
Under a high power the structure of the investing hairs
is very interesting ; for they are seen to be flat filaments
of the yellow chitine, very much dilated at their bases,
U2
EVENINGS AT THE MICROSCOPE.
and set side by side in regular whorls, the bottom edges
of which form the rings of which the tongue is composed.
The tip is probably a sensitive organ of taste, for it ter-
minates in a minute globose pulpy body, whose surface is
beset with tiny curved points. Thus I have pointed out
to you, in this Bee, all the parts which enter into the
JAWS OF BEE.
mouth of the Beetle, except the maxillary palpi; and
these, very small indeed, but quite distinct, you may see
on the outer edge of the maxillw, just below the point
where their outline begins to swell into its graceful curve.
The cylindrical tongue is capable of considerable ex-
INSECTS : THEIR MOUTHS. 143
tension and contraction at the will of the animal ; being
sometimes pushed far out of the mouth, and at others
quite concealed within its sheath. " The manner," ob-
serves Mr. Newport, "in which the honey is obtained,
when the organ is plunged into it at the bottom of a
flower, is by 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
maxillce above, and of the labial palpi, and this part of
the ligula below."
"Well might Swammerdam, when describing this ex-
quisite structure, humbly exclaim : — " I cannot refrain
from confessing, to the glory of the immense and incom-
prehensible Architect, that I have but imperfectly de-
scribed and represented this small organ ; for, to repre-
sent it to the life in its full perfection, as truly most
perfect it is, far exceeds the utmost efforts of human
knowledge."
Here you may see the implement with which the Bug
performs its much-dreaded operation of blood-sucking ;
for though this is not the head of the Bed-bug, but of
one of the winged species that are found so abundantly
on plants, and which I have just obtained by beating
the hedge at the bottom of my garden, yet the structure
of the mouth is so exactly alike in all the members of
this immense family, that one example will serve for all
others.
From the front of the head, which, owing to the manner
in which this part is carried, is the lower part, proceeds a
fine thread, about four times as long as the head itself,
passing along between the fore legs, ' close to the body
beneath the breast. It is, however, at the pleasure of
the animal, capable of being brought up so as to point
directly forward, and even projected in front of the head,
144 EVENINGS AT THE MICROSCOPE.
and in the same plane as the body ; a fact which once
came under my own observation. I found a Plant-bug
(Pentatoma) which had plunged this thread-like sucker
of his into the body of a caterpillar, and was walking
•about with his prey, as if it were of no weight at all,
•carrying it at the end of his sucker, which was held
straight out from the head, and a little elevated. He
fiercely refused to allow the poor victim to be taken
away, being doubtless engaged in sucking its vital juices,
just as the bed-abomination victimises the unfortunates
who have to sleep at some village inn.
Well, we put this head with its sucker between the
plates of the compressorium, upon the microscope-stage.
The thread is an organ composed of four lengthened
slender joints, beset with scattered bristles, and termi-
nating in a point on which are placed a number of
exceedingly minute radiating warts, probably the seat of
some sensation ; perhaps taste. This jointed organ is the
under-lip ; it is slit all down one surface, so that it forms
an imperfect tube, or furrow, within which lies the real
weapon, a wire of far greater tenuity, which by pressure
I can force out of its sheath. It is so slender that its
average diameter is not more than TttV otn °^ an inch, and
it ends in the most acute point ; yet this is not a single
body, but consists of four distinct wires, lying within one
another, and representing the maxilke and the mandibles.
These can be separated by the insect, and will sometimes
open when under examination ; but no instrument that
I can apply to them is sufficiently delicate to effect their
separation at my pleasure. Just at the very tip, however,
under this high power, we can see, by the semi-trans-
parency of the amber-coloured chitine of which the organ
composed, that there is another tip a little shorter, and,
as it were, contained within the other. This inner point
is cut along its edges into saw-teeth pointing backward.
Such exquisite mechanism is bestowed upon the structure,
INSECTS : THEIR MOUTHS. 145
and such elaborate contrivance is displayed for the comfort
of an obscure and offensive insect, by Him Who has not
disdained to exercise His skill and wisdom in its creation !
You know the stout flies which are denominated Horse-
flies or Whame-flies (Tabanus), which are so numerous
in the latter part of summer, flying around horses, and
men too, if we intrude upon their domains. They are
continually alighting on the objects of their attentions,
and, though driven away, returning with annoying per-
tinacity to the attack. You may always recognise them
by the brilliant metallic hues — reds, yellows, andgreens —
with which their large eyes are painted, often in stripes
or bands. These are voracious blood-suckers ; and, as
might be supposed from their propensities, they are well
furnished with lancets for their surgery. Here you
may see their case of instruments, which are so effective,
that Reaumur tells us that, having compelled one to
disgorge the blood it had swallowed, the quantity
appeared to him greater than the whole body of the
insect could have been supposed capable of containing.
All the parts here are formed of the common amber-
coloured chitine, brilliantlv clear and translucent. The
upper lip forms a sort of straight sheath, in which all the
other parts are lodged when not in use. The mandibles
are narrow lancets, of which one edge near the tip is beset
with reverted saw-teeth, and the opposite edge with
exceedingly sharp points standing out at right angles ;
while the surface is roughened with lozenge shaped knobs
set in regular rows. Below these are the maxilla', which
are the principal cutting instruments ; these are shaped
like a carving-knife with a broad blade, strengthened at
the basal part of the back by a thick ridge, but brought to
a double edge near the tip. The back-edge is perfectly
fine and smooth, so that the highest powers of the micro-
scope can only just define its outline, while the other edge
is notched into teeth so delicate that twelve of them are
L
146 EVENINGS AT THE MICROSCOPE.
cut in the length of a ten-thousandth part of an inch;
and yet they are quite regular and symmetrical in
length, height, and form ! I know of no structure of
the kind which equals this. These teeth are continued
throughout the inner edge of the blade from the tip to
the base, and are about eight hundred in number ;
though the length of the entire blade is only such that
upwards of a hundred and fifty of them, if laid end to
end, would not reach to the extent of an inch !
The office of these wonderful instruments is doubtless
to cut and enlarge the wound within, and thus promote
the flow of blood. The whole apparatus is plunged into
the flesh of the victim — horse or man; then the maxillce
expand, cutting as they go, and doubtless working to and
fro as well as laterally, so as to saw the minuter blood-
vessels. At the same time the mandibles, with their
saw-teeth on one side, and pricking points on the other,
work in like manner, but seem to have a wider range.
Finally, there is an exceedingly delicate piece beneath
all, which seems to represent the labium or under lip.
In the active and cunning little Flea, that makes his
attacks upon us beneath the shelter of the blankets and
under cover of night, the piercing and cutting blades are
very minute, and have a peculiar armature. They remind
me (only in miniature of course) of those formidable flat
weapons wrhich w^e often see in museums, the rostrums of
the huge Saw-fishes (Pristis) ; a great plate of bone
covered with grey skin, and set along each side with a
row of serried teeth. Here the blades are similar in form,
being long, straight, narrow plates of transparent chitine,
set, along each edge, with a double row of glassy points,
which project from the surface, and are then hooked
backwards. These are the mandibles, and they closely
fold together, inclosing another narrower blade, the
upper lip, which has its two edges studded with similar
points, but in a single row.
insects: their mouths. 147
In general, as we have seen, the maxillce are the
specially armed weapons ; the mandibles acting a secon-
dary part, often serving as mere sheaths in those insects
which pierce other animals Avith the mouth. But in
this case the mandibles are the favoured parts, the
maxillce being developed into broad leaf-shaped convex
sheaths, inclosing the mandibles.
There are, however, two cutting blades besides ; the
labial palpi, which have their upper edge thick, divided
into four distinct joints, and set with bristles, thus re-
taining the proper character of palpi ; while their under
edge is thinned away to a fine keen blade, in which there
is no sign of jointing. Then there are the maxillary
palpi, of which the joints are furnished at their tips with
tiny projecting warts, doubtless the seats of a delicate
sense, and hollowed into a double series of chambers,
which are filled with a dark-coloured fluid.
All this is very interesting to behold, and is calculated
to exalt our ideas of the wonderful and inexhaustible
resources of Omnipotence, as well as to humble us, when
we reflect how little we certainly understand even of
what we see. But, common as the Flea is, it is not a
matter of course that you will be able to repeat these
observations with the first specimen you put on the stage
of your microscope. Several favourable conditions must
combine in order to insure a successful examination.
You should choose a female Flea, partly because of her
greater size, and partly because the predatory weapons,
in all these piercing and sucking insects, are better de-
veloped in the females, — true Amazons. Then you will
find it needful to amputate the head, in order to get rid
of the front legs, the thick thighs of which else impede
your sight of the mouth, being projected on each side of
it. And this is a delicate operation; it must be per-
formed on a plate of glass, under a lens, with one of
those dissecting needles whose points are ground to a
l 2
148 EVENINGS AT THE MICROSCOPE.
cutting-edge. Next, having severed the head, you must
place it in a drop of water, between the plates of your
compressorium, the graduated pressure of which, by
means of the screw, will cause the organs of the mouth
to open and expand separately. Finally, you must have
a good instrument, and a high power : less than 600
diameters will not avail to bring out distinctly the
toothing of the mandibles and labrum ; and even then
you will need delicate manipulation and a practised eye.
But the object is worthy of the care bestowed upon it.
Once more. Let us submit to examination the com-
plex case of instruments wherewith the Gnat performs her
unwelcome yet skilful surgery. I say " her," because
among the Gnats also, as I have just intimated, it is the
females only who possess skill in the art of bleeding ;
the males being innocent of any share in it, and being
indeed unprovided with the needful implements.
Here is a large specimen, resting with raised hind legs
on the ceiling, and now in alarm off with shrill humming
flight to the window. I decapitate her without com-
punction, as it is but a fair penalty for her murderous
deeds ; and as, of old, the axeman held up " the head
of a traitor " to public gaze, so I lay this head on the
glass of the compressorium for your contemplation.
And before I apply pressure to the glass-plate, devote
a moment's attention to the head as a whole. First, the
head itself is a hemisphere, almost wholly occupied with
the two compound eyes, which present the beautiful ap-
pearance of a globe of black velvet, studded with gold
buttons arranged in lines crossing each other at right
angles. The summit of the head, where the two com-
pound eyes unite, bears a sort of rounded pedestal, the
area of which forms the sole part of the head not covered
by the organs of vision. On this are placed, side by side,
the two antennae, springing from rounded bulbous bases;
they consist of twelve (exclusive of the basal bulb) cylin-
INSECTS : THEIR MOUTHS. 140
clrical joints, which are beset on all sides with short
arched hairs, but have besides a whorl of radiating long
hairs surrounding the bottom of each joint. The effect
of this is exceedingly light and elegant.
Between these projects a long cylinder, which repre-
sents the lower lip (labium) ; it slightly swells towards
the tip, where it forms a round, nut-like knob, covered
with exceedingly minute papilla1, and no doubt consti-
tuting a highly sensitive organ of touch. For the greatest
part of its length it is covered with lined scales, and with
short arched hairs like the antennae, while each side of
its base is guarded by a labial palp of three joints.
On applying a graduated pressure, slowly increased to
actual contact of the plates (or as near an approximation
to it as we can effect), we see first that the nut-like tip
of the labium expands into two concave leaves, like the
bracts of a bud, and displays two pairs of more delicate
leaves within them. Then, from a groove along the upper
side of the labium spring out several filaments, of great
elasticity, and of the most delicate tenuity. One pair of
these represent the mandibles ; they consist each of a
very narrow blade, with a stronger back like that of a
scythe. Their tip is brought to a most acute point, and
the edge in immediate proximity to this is cut into about
nine teeth, pointing backward ; the rest of the edge is
smooth, but the whole blade is crossed by a multitude of
oblique lines of great delicacy, which may be intended
to keep the edge constantly keen.
Next come the maxillce, or lower jaws, horny filaments
as long as the former, but still more delicate, constituting
simple cutting lancets, with a back and a keen blade, a
little widening at the tip.
Besides these there is the tongue, consisting of a cen-
tral rod which is distinctly tubular, and of a thin blade
on each side, fine-edged and drawn to an acute point.
And also the labrum or upper lip, an organ having the
150
EVENINGS AT THE MICROSCOPE.
same general form, but constituting an imperfect tube ;
a tube, that is to say, from which about a third of the
periphery is cut away, so as to serve as a sheath for the
tongue, which ordinarily lies within its concavity.
I scarcely know whether this
apparatus is not more wonder-
fully delicate than any we have
examined — even than that of the
Flea. And how effective it is you
doubtless well know; for when
the array of lancets is introduced
into the flesh, you are aware
that a tumour is left, which, by
its smart, itching, and inflamma-
tion, causes much distress, and
lasts many hours. This effect is
probably produced partly by the
deep penetration of the instru-
ments— for they are fully one-
sixth of an inch in length, and
they are inserted to their very
base — and partly by the injection
of a poisonous fluid, intended, as
has been conjecturally suggested.
to dilute the blood, and make it
more readily flow up the capil-
lary tubes. The channel through
which this fluid is ejected is pro-
bably the tongue, which you see
to be permeated by a tube containing a fluid ; and the
same channel may afford ingress to the diluted blood.
The labium does not enter the wound. If you have
ever had the philosophic patience to watch a gnat while
puncturing your hand, you have observed that the knob
at the end of the proboscis is applied to the skin, and that
then the organ bends with an angle more and more acute,
LANCETS OF FEMALE GNAT.
a, labium. d, tongue.
b, b, mandibles. e, labium.
c, c, maxillae.
INSECTS I THEIR MOUTHS.
151
until at length it forms a double line, being folded on
itself, so that the base is brought into close proximity to'
the skin. Meanwhile the lancets have all been plunged
in, and are now sunk into your flesh to their very bottom,
while the labium, which formed merely the sheath for
the whole, is bent up upon itself, ready again to assume
its straight form, as soon as the disengaged lancets require
its protection.
TONGUE OF BLOW-FLT.
The tongue of one of the common Flies (House-fly,
Blow-fly, &c), is an exquisite microscopical object, from
its extreme complexity and beauty. You are familiar
with the way in which a fly, having alighted close to a
drop of tea on the table, applies to it a proboscis with large
dilated extremity, and presently licks it all up. You shall
now see the curious implement by which this is effected.
152 EVENINGS AT THE MICROSCOPE.
The broad portion of the object before us, forming its
bottom part, bristling with coarse black hair, is the front
of the head of a Blow-fly. From the midst of this pro-
jects a dark brown mass terminating in two points, and
inclosing a narrower and darker object with two long
slender roots, dilated at their bases ; this is the pair of
maxillce, altered and modified into a kind of sheath for
the mandibles. On each side projects an elegant club,
bristled with coarse black hair, and covered besides with
a coat of very minute hairs; these clubs are the maxillary
palpi.
But now we come to the terminal part, consisting of a
pair of lobes, together forming a rounded triangle in their
outline. This is the dilated and thickened termination of
the labium, and is the instrument by which the liquids
are so rapidly sucked up. It is impossible to describe
this beautiful structure intelligibly ; and, indeed, it is
not well understood even by those who have devoted their
lives to this branch of natural science. The principal
feature apparent is a wide clear membrane, through
which runs with admirable symmetry a series of tubes.
These tubes consist of four primary ones, all originating
near the centre of the expansion, and radiating thence,
two backward towards the two lateral angles of the
triangle, and the other two nearly side by side towards
its point. From each of these, along its outer side only,
branch off the minor tubes, very numerous and close
together, going off in a slightly sinuous line direct to
the margin, diminishing regularly in their course, and
at their extremities curving over, so as to bring their
open tips to the surface of the skin.
The construction of these tubes is highly interesting :
they are formed, like the air-pipes (trachece), of a multitude
of horny rings ; but with this peculiarity, that the rings
do not form a continuous spiral, but are separate and
distinct, and are moreover imperfect ; for each wire (so to
INSECTS : THEIR MOUTHS. 153
speak) does not perform a complete circle, but only about
two-thirds of a circle, leaving a blank space ; and the tips
of the wires end alternately in a fine acute point, and in a
rounded fork, like the prongs of a pitch-fork. It has been
said that these tubes are modified trachece; but this fact is
by no means obvious to me; for, so far from their being
connected with the general tracheal system, each of the
four main tubes originates in an open centre, and each
lias an open extremity. I think it likely that they are so
many suctorial pipes, through which the fluid to be drunk
is drawn up, entering at their minute open tips, and dis-
charging itself into the central cavity by the open basal
extremities of the main tubes.
The most extraordinary modification of jaws, however,
is the long spiral tube which is ordinarily coiled up under
the face of a Butterfly or Moth, with which it sucks up
the sweet nectar of flowers. Many flowers have a deep
corolla, and most have the bases of their petals, where
the nectar lies, so far from the level of the surface that
probing is necessary to reach it. Bees can enter tubular
flowers, and lick their bottoms; and even blossoms that
are closed, as the Snapdragon, they know how to force
and enter. But Butterflies, with their wide wings, in
capable of being folded, cannot enter flowers bodily, and
therefore a peculiar apparatus is given them for stealing
their contents, as it were, at the doors.
Nothing is easier than to examine this beautiful organ
with the naked eye; and much may be learned of its
structure by means of a pocket lens. You may thus see
in a moment that it forms a flat spiral of several coils,
like the mainspring of a watch; that it runs off to a point,
and that this point is double, for it is frequently seen
separate a considerable way up. Hence you would pro-
bably infer that the organ consists of two equal and
similar halves, united lengthwise. And so, indeed, it does;
and these halves are the representatives of the maxillce or
154 EVENINGS AT THE MICROSCOPE.
lower jaws of the Beetle, being thus greatly developed at
the expense of almost all the other parts. The upper lip
and the mandibles are discernible only in the form of
three most minute plates ; the labial palpi are large and
prominent, those well-haired points that project in front
of the head, one on each side of the spiral. This spiral
form of the maxillce is called antlia.
It is not, however, very easy to fix it in an extended
condition on a slip of glass, so as that it shall lie flat
throughout its whole length, without injuring the parts
or so agglutinating them together that their structure
is concealed or distorted, and in either case unfitted
for microscopical examination. The specimen which I
have prepared, from the mouth of the Small Garden
White Butterfly, is stretched, and fixed in balsam, and
will, I think, show you the structure under a high power
very well.
Before we examine it, however, I will cite you the
description of one of the most eminent of microscopical
anatomists, Mr. Newport. He considers each maxilla to
be composed of an immense number of short transverse
muscular rings, which are convex externally and concave
internally, the two connected organs forming a tube.
Within each there are one or more large trachece con-
nected with the trachece in the head. The inner or con-
cave surface which forms the tube is lined with a very
smooth membrane, and extends along the anterior margin
throughout the whole length of the organ. At its com-
mencement at the tip it occupies nearly the whole breadth
of the organ, and is smaller than at its termination
near the mouth, where the concavity or groove does not
occupy more than about one-third of the breadth. In
some species, the extremity of each maxilla is furnished
along its anterior and lateral margin with a great number
of minute papilla?. These, in Vanessa A talanta (the Bed
Admiral Butterfly), for instance, form little barrel-shaped
insects: their mouths. 155'
bodies, furnished at the free end with three or more
marginal teeth, and a larger pointed body in the centre.
There are seventy-four of these in each maxilla, or half
the proboscis. Mr. Newport regards them as probably
organs of taste. There are also some curious appendages
arranged along the inner anterior margin of each maxilla,
in the form of minute hooks, which, when the proboscis
is extended, serve to unite the two halves together, by
the point of the hooks in one half being inserted into
little depressions between the teeth of the opposite
side ; sometimes these are furnished with a tooth below
their tips.
With all deference to so respectable an authority, I
cannot help seeing that such is not the structure of the
antlia before us. It is evident to me that each half tube
is composed of a membrane stretched upon stiff horny
semi-rings., doubtless composed of chitine, and certainly
not muscular. By bringing the outline of the rounded
exterior into focus, we see that these rings form sharp
ridges ; and by tracing them onwards to the attenuated
extremity of the organ, we see them gradually give way
to transverse lines of interrupted ridgy warts upon the
outside of the membrane. The true muscles appear to
be indicated by those oblique lines and bands that are
seen in the interior, beneath the horny rings.
This specimen shows very distinctly that the two sides
are but semi-tubular ; and, as one pair of the opposing
edges are open at each extremity, and the other pair
separate throughout, we are able to discern very clearly
the array of hooks, by which the edges are united at the
will of the animal. No trace of the curious little
I ointed barrel-shaped papillce is found here, but I have
set n them in other examples.
It seems highly probable, from the observations of
the excellent anatomist just named, that the exhaustion
of the nectar of a flower, which is effected with great
156
EVENINGS AT THE MICROSCOPE.
THE StTCKEE OF A BUTTERFLY.
A small portion of one half-
cylinder.
rapidity and completeness, is a process dependent on
respiration, and connected with the air-pipe that per-
meates each division of the sucker.*
It will not be a very violent
transition if from the sucking-
pump of the Butterfly I carry you
to the silk-spinner of the Cater-
pillar. Here I have a Silkworm
in the act of beginning: its co-
coon; by inclosing which in this
glass tube we shall conveniently
have the insect at command, and
shall be able to view the process
under a low magnifying power
and reflected light. Now the grey
faSe of the worm is presented to
us ; and we can see, below the edge
of the head-shield, a short broad
upper lip, forming two blunt points. Below this is the
pair of strong brown mandibles, convex outwardly and
concave inwardly, each cut at its broad biting edge into
several teeth. Below these are two little points which
represent the maxillce, and between them a blunt rounded
knob, which is the lower lip (labium).
You may also see on each cheek, close to the base of
the mandible, a little pit, out of which rises a short
columnar organ tipped with two bristles ; these columns
are the incipient antennae, Outside them you may dis-
cern, on each cheek, a series of six globes of glass (so
they appear) set in the substance of the skin, — five
forming a semicircle, and one in the centre ; these ; re
* Mr. Darwin, in his admirable work On the Fertilisation of Orchids,
p. 33 et seq., has shown that the tubular proboscis of Lepidoptera,
while used by the insect solely for the collection of nectar, is indirectly
and unintentionally used for the transferring of pollen-grains from
flower to flower ; and thus becomes a most important agent in the pro-
pagation of plants. (See his remarkable figure on p. 37 op. cit.)
INSECTS : THEIR MOUTHS. 157
" the windows at which the [silkworm's] soul looks
through " — provided he has any soul ; in prosaic par-
lance, his eyes.
Now, having thus introduced the several members of
our useful friend's physiognomy to you, let me call your
attention to a fleshy wart just beneath the lower lip, and
midway between the bases of the two fore legs. This
wart terminates in a horny point not unlike a bird's beak,
which is perforated, and from the tip of which the glisten-
ing yellow filament of silk is ever drawn out, as the cater-
pillar throws his head from side to side. This pointed
wart is the spinning organ ; and the thread of silk is,
as it issues from the orifice, a fluid gum, which hardens
immediately on its exposure to the air. The silk gum is
secreted by the caterpillar in two long blind tubes, which
lie twisted and coiled in the interior of the body, occupy-
ing nearly the whole space, except that which is taken
up by the great digestive canal. These become very
slender as they approach the head, and at length termi-
nate in a reservoir, which opens by the little pointed
wart which you have just seen.
Many caterpillars are able to suspend themselves at
pleasure by means of the thread which they are spinning,
lengthening it and "stopping it off," at will. This latter
operation they perform (though they cannot recal the
thread when once it has issued) by means of an angular
point formed by the two slender tubes at their junction
in the reservoir; thus compressing the thread of gum, and
so preventing any more from issuing. The gum is per-
fectly colourless in the reservoir; but, as it issues forth,
it becomes coated with a varnish, which is secreted in the
same organ, and which is poured out at the same time.
In the case of the common Silkworm, this varnish
imparts to the silk that brilliant yellow hue which it
generally possesses, and which, as the varnish is soluble,
can be easily discharged from it in the manufacture.
158 EVENINGS AT THE MICROSCOTE.
CHAPTER X.
INSECTS : THEIR EARS AND EYES.
A very wide field of observation, and one easily culti-
vated, is presented by the organs of sense in the Insect
races, and in particular by those curious jointed threads
which proceed from the front or sides of the head, and
which are technically called antennce. These may some-
times be confounded with the palpi, examples of which
organs we have been lately looking at ; for in a carnivo-
rous Beetle, for instance, both palpi and antennce are
formed of a number of oblong, polished hard joints, set
end to end, like beads on a necklace. And it is probable
there may be as much that is alike in the function as in
the form of these two sets of appendages ; that both are
the seats of some very delicate perceptive faculty allied
to touch, but of which we cannot, from ignorance, speak
very definitely. It is likely, indeed, that sensations of
a very variable character are felt by them, according to
their form, the degree of their development, and the
habits of the species.
It is not impossible, judging from the very great diver-
sity which we find in the form and structure of these and
similar organs, in this immense class of beings, compared
with the uniformity that prevails in the organs of sense
bestowed on ourselves and other vertebrate animals, —
that a far wider sphere of perception is open to them
than to us. Perhaps conditions that are perceptible to
us, only by the aid of the most delicate instruments of
modern science, may be perceptible to their acute facul-
insects: their ears and eyes. 159
ties, and may govern their instincts and actions. Among
such we may mention, conjecturally, the comparative
moisture or dryness of the atmosphere, delicate changes
in its temperature, in its density, the presence of gaseous
exhalations, the proximity of solid bodies indicated by
subtle vibrations of the air, the height above the earth
at which flight is performed, measured barometrically,
the various electrical conditions of the atmosphere ; and
perhaps many other physical qualities which cannot be
classed under sight, sound, smell, taste, or touch, and
which may be altogether imperceptible, and therefore
altogether inconceivable, by us. It is probable, however,
that the antennae, are the organs in which the sense of
hearing is specially seated; a conclusion which has long
been conjecturally held, and which is confirmed by some
observations recently made on the analogous organs in
the Crustacea^ which I will allude to more particularly
presently.
The forms which are assumed by the antennae of Insects
are very various; and I can bring before you only a very
small selection out of the mass. One of the most simple
forms is that found in many Beetles, as in this Carabas,
for example. Here, each antenna is composed of eleven
joints, almost exactly alike and symmetrical, each joint a
horny body of apparently a long-oval shape, polished on
the surface, but not smooth, because covered with minute
depressed lines, and clothed with shaggy hair. There is,
however, a slight illusion in the appearance : it seems as
if the dividing point of the joints were, as I have just
said, at the termination of the oval, but when we look
closely we see that the summit of each oval is, as it were,
cut off by a line, and by comparing the basal joints with
the others, we see that this line is the real division, that
the summit of the oval really forms the bottom of the
succeeding joint, and that the constricted part is no
articulation at all. The first, or basal joint (called the
160 EVENINGS AT THE MICROSCOPE.
scajms), and the second (called the pedicella), differ in
form from the rest here but slightly, but often consider-
ably. The whole of the remaining joints are together
termed the clavola.
You may see a considerable variety of figure and of
aspect generally in this tiny Weevil, which may be ac-
cepted as a representative of a great family of Beetles,
the Curcidionidce. The manner of their insertion strikes
us at first sight as peculiar, as is in fact the aspect of the
whole head. Instead of a thick substantial solid front,
with powerful widely-gaping jaws, such as we saw in the
Carabs, a long rod-like proboscis here projects from
between the eyes, as long as the whole animal, curving
downwards, and carrying at its very extremity a minute
mouth, with all the proper apparatus of lips, jaws, and
palpi. Moreover, the antennce are planted on the two
sides of this beak, about its mid-length; and they are
curiously elbowed, each projecting horizontally at a right
angle to the beak for a considerable distance, and then
with a sharp angle becoming parallel to it for the re-
mainder of their length. So that, supposing the terminal
half of the beak to be broken off just behind the insertion
of the antennce, the whole would compose the letter T.
Now, the first bend of this angle is composed of a single
joint, the scapus, which is, in this family, greatly length-
ened ; and then the two or three final joints are much
thicker than all the others, and are as it were fused
together into a large oval knob, called the club.
Now, a word or two in explanation of this very singular
form of head and head-organs. The larva or grub stage
of these insects is destined to be passed in the interior
of fruits and seeds; the individual which we have been
examining (Balaninus nucum) was born one morning in
August, in the interior of a hazel-nut. Its parent had
chosen a suitable nut, just then when it was set for fruit
and as yet green and soft ; and had with her proboscis,
insects: their ears and eyes. 161
or rather with her jaws at its tip, as with a gimlet, bored
a tiny hole through the yielding shell into the very in-
terior ; then, turning round, and inserting the extremity
of her abdomen, with its ovipositor, she had shot an egg
into this dark cavity. The juices poured forth at the
wound soon healed the orifice ; the nut grew ; and pre-
sently the egg became a little Avhite grub. He then
rioted in plenty ; prolonged his darkling feast
" From night to morn, from morn to dewy eve.;"
— 'twas all " dewy eve " to him, by the way, for no ray of
light saw he, till that prosperous condition of existence
was done. Xo wonder he grew fat ; and fat those rogues
of nut-weevils always are, as you well know. Well,
when the nut fell, in October, the kernel was all gone,
completely devoured, and our little highway-robber was
ready for his winter sleep ; he gnawed a fresh hole
through the now hard shell, made his way out, and
immediately burrowed into the earth, where he lay till
June ; then became a pupa, and emerged just what you
see him, a long- snouted beetle like his mother, in the
beginning of August.
Such is his " short eventful history ; " and you now
see that the long beak is formed entirely with reference
to this economy : it is an auger, fitted to bore holes into
shell-fruits, through their envelopes, for the reception of
eggs.
There is a very extensive family of Beetles known as
Lamellicomes, because the antennal joints are singularly
flattened, and applied one over the other, like the leaves
of a book (lamella, a leaf). Here is a very common little
€hafer found on the droppings in pastures (Aphodius
Jimetarius), in which the last three joints, constituting the
-club of the antenna, are of an ovate form, and flattened,
so as to lie one on another quite close, like three oval
M
162
EVENINGS AT THE MICROSCOPE.
cakes ; and being connected only at one end of the long
axis, they open and shut at the pleasure of the animal,
like a long pocket memorandum -book of three leaves.
But this structure is seen to still greater advantage in
the much larger Cockchafer, so abundant in May in some
seasons. For here the joints composing the club are
much more numerous (seven in the male, six in the
female), and they are proportionally longer and thinner,
and therefore more leaf-like. The insect widely expands
them, evidently to receive impressions from the atmo-
A>'TE>"NA OF COCKCHAFER.
sphere ; when alarmed, they are closed and withdrawn
beneath the shield of the head ; but, on the first essay
towards escape, or any kind of forward movement, the
leaves are widely opened, and then, after an instant's
pause to test the perceptions on the sensorium, away it
travels.
In some Beetles each joint of the series has one of its
outer angles more developed than the other, and so pro-
duced as to make, with the rest of the joints, a saw-like
edge ; you may see an example in this Click-beetle or
INSECTS : THEIR EARS AND EYES. 163
Skipjack (Elater), but many members of the same family
show the same structure in a far higher degree, the
angle being drawn out into a long slender rod, which
(with its fellows) imparts to the antenna the appearance
of a comb.
But much more curious and beautiful are the antennae
of many moths, which often resemble feathers, particu-
larly in the group Bombycina, of which the Silkworm is
an example : and in the male sex, which displays this
structure more than the female. But I will show you a
native example.
This is the antenna of a large and handsome, and not
at all uncommon, moth, the Oak Egger (Lasiocampa
quercvs). It consists of about seventy joints, so nearly
alike in size and outline, that the whole forms an almost
straight rod, slightly tapering to the tip. Each joint,
however, sends forth two long straight branches, so dis-
posed that the pair make a very acute angle, and the
whole double series of seventy on each side, form a deep
narrow groove. These two series of branches, being per-
fectly regular and symmetrical, impart to the antennse
the aspect of exquisite feathers.
It is. however, when we examine the elements of this
structure in detail, using moderately high powers of
enlargement, that we are struck with the elaborateness
of the workmanship bestowed upon them. Each of the
lateral branches is a straight rod, thick at its origin,
whence it tapers to a little beyond its middle, and then
thickens again to its tip. Here two horny spines project
from it obliquely, one much stouter than the other, at
such an angle as nearly to touch the tip of the succeed-
ing branch.
Besides this, each branch is surrounded throughout
its length with a series of short stiff bristles, very close-
set, projecting horizontally (to the plane of the axis of
the branch), and bent upwards at the end candelabrum-
H 2
164
EVENINGS AT THE MICROSCOPE.
fashion. The mode in which they are arranged is in a
short spiral, which makes about forty-rive whorls or
turns about the axis ; at least in the branches which are
situated about the middle of the antenna ; for these
diminish in length towards the extremity, bringing the
feather to a rather abrupt point.
The entire surface of the branch gleams under re-
flected light with metallic hues, chiefly yellows and bronzy
greens ; which appear to depend on very minute and
closely-applied scales that overlap each other. The main
stem of the feather, — that is, the primary rod or axis, —
is somewhat sparsely clothed with scales of another kind,
thin, oblong, flat plates, notched at the end, and very
slightly attached by means of a minute stem at the
base, —the common clothing-scales of the Lepidoptera,
specimens of which we have before examined.
POKTION OF ANTENNA OF OAK EGGER MOTH.
We may acquire some glimpse of a notion why this
remarkable development of antennae is bestowed upon the
male sex of this moth, by an acquaintance with its habits.
It has long been a practice with entomologists, when they
have reared a female moth from the chrysalis, to avail
themselves of the instincts of the species to capture the
insects: their ears and eyes. 165
male. This sex has an extraordinary power of discover-
ing the female at immense distances, even though she be
perfectly concealed; and will crowd towards her from all
quarters, entering into houses, beating at windows, and
even descending chimneys, to come at the dear object of
their solicitude. Collectors call this mode of procuring
the male " sembling," that is " assembling" because the
insects of this sex assemble at one point. It cannot be
practised with all insects, nor even with all moths; with
this family, Bombycidce, it is in general successful ; and of
these, none is more celebrated for the habit than the Oak
Egger. The very individual whose antenna has furnished
us with this observation was taken in this way; for having
bred a female of this species the evening before last, I put
her into a basket in my parlour. One male, the same
evening, came dashing into the kitchen ; but yesterday,
soon after noon, in the hot sunshine of August, no fewer
than four more males came rapidly in succession to the
parlour window, which was a little open, and, after beat-
ing about the panes a few minutes, found their way in,
and made straightway for the basket, totally regardless
of their own liberty.
It must be manifest to you that some extraordinary
sense is bestowed on these moths, or else some ordinary
and well-known sense in extraordinary development. It
may be smell ; it may be hearing ; but neither odour nor
sound, perceptible by our dull faculties, is given forth by
the females : the emanation is far too subtle to produce
any vibrations on our sensorium, and yet sufficiently
potent, and widely diffused, to call these males from their
distant retreats in the hedges and woods. I think it
highly probable that the great increase of surface given
to the antenna; by the plumose ramification we have been
observing, is connected with the faculty; perhaps every
bristle of the spiral whorls is a perceptive organ, con-
structed to vibrate with the tender undulations that circle
166 EVENINGS AT THE MICROSCOPE.
far and wide from the new-born female, Surely the ways
of God in creation are " past finding out."
The male Gnat presents in its antennae a pair of plumes
of equal beauty, but of a totally different character.
The pattern here is one of exceeding lightness and grace,
as you may see in this specimen. Each antenna is essen-
tially a very slender cylindrical stem of many joints (about
fourteen); at each joint springs out a whorl of fine hairs
of great length and delicacy, which radiate in various
directions (not, however, forming a complete circle),
curving upward like the outline of a saucer, supposing
the stem to be inserted into its centre. The length of
these hairs is so great, that the diameter of their sweep
equals, if it does not exceed, the whole length of the
antenna.
In the tribe of two-winged insects, which we term par
excellence Flies (Muscadce), the antenna? are of peculiar
structure. The common House-fly shall give us a good
example. Here, in front of the head, is a shell-like con-
cavity, divided into two by a central ridge. Just at the
summit of this project the two antenna?, originating close
together, and diverging as they proceed. Each antenna
consists of three joints, of which the first is very minute,
the second is a reversed cone, and the third, which is
large, thick, and ovate, is bent abruptly downwards imme-
diately in front of the concavity. From the upper part
of this third joint projects obliquely a stiff bristle or style,
which tapers to a fine point. It is densely hairy through-
out ; and is, moreover, beset with longer hairs, on two
opposite sides, which decrease regularly in length from
the base, making a wide and pointed plume.
Such are a few examples of what are presumed to be
the ears of Insects; let us now turn our attention to their
eyes. And we can scarcely select a more brilliant, or a
larger example, than is presented by this fine Dragon-fly
(sEshna), which I just now caught as it was hawking to
insects: their ears and eyes. 167
and fro in my garden. How gorgeously beautiful are
these two great hemispheres that almost compose the
head, each shining with a soft satiny lustre of azure hue,
surrounded by olive-green, and marked with undefined
black spots, which change their place as you move the
insect round !
Each of these hemispheres is a compound eye. I put
the insect in the stage-forceps, and bring a low power to
bear upon it with reflected light. You see an infinite
number of hexagons, of the most accurate symmetry and
regularity of arrangement. Into those which are in the
centre of the field of view, the eye can penetrate far
down, and you perceive that they are tubes ; of those
which recede from the centre, you discern more and more
of the sides ; while, by delicate adjustment of the focus,
you can see that each tube is not open,but is covered with
a convex arch of some glossy matter, polished and trans-
parent as crystal. There are, according to the com-
putations of accurate naturalists, not fewer than 24,000
of these convex lenses in the two eyes of such a large
species of Dragon-fly as this.
Every one of these 24,000 bodies represents a perfect
eye ; every one is furnished with all the apparatus and
combinations requisite for distinct vision ; and there is
no doubt that the Dragon-fly looks through them all. In
order to explain this, I must enter into a little technical
explanation of the anatomy of the organs, as they have
been demonstrated by careful dissection.
The glassy convex plate or facet in front of each
hexagon is a cornea or comeule, as it has been called.
Behind each cornea, instead of a crystalline lens, there
descends a slender transparent pyramid, whose base is
the cornea, and whose apex points towards the interior,
where it is received and embraced by a translucent cup,
answeriDg to the vitreous humour. This, in its turn, is
surrounded by another cup, formed by the expansion of a
168 EVENINGS AT THE MICROSCOPE.
nervous filament arising from the ganglion, or knot, on
the extremity of the optic nerve, a short distance from
the brain. Each lens-like pyramid, with its vitreous cup
and nervous filament, is completely surrounded and
isolated by a coat (the choroid) of dark pigment, except
that there is a minute orifice or pupil behind the cornea,
where the rays of light enter the pyramid, and one at
the apex of the latter, where they reach the fibres of the
optic nerve.
Each cornea is a lens with a perfect magnifying power ;
as has been proved by separating the entire compound
eye by maceration, and then drying it, flattened out by
pressure, on a slip of glass. When this preparation wajs.
placed under the microscope, on any small object, as the
points of a forceps, being interposed between the mirror
and the stage, its image was distinctly seen, on a proper
adjustment of the focus of the microscope, in every one
of the lenses whose line of axis admitted of it. The focus
of each cornea has been ascertained by similar experi-
ments to be exactly equal to the length of the pyramid
behind it ; so that the image produced by the rays of light
proceeding from any external object, and refracted by
the convex cornea, will fall accurately upon the sensitive
termination of the optic nerve-filament there placed to
receive it.
The rays which pass through the several pyramids are
prevented from mingling with each other by the isolating
sheath of dark pigment; and no rays, except those which
pass along the axis of each pyramid, can reach the optic-
nerve; all the rest being absorbed in the pigment of the
sides. Hence it is evident, that as no two cornea? on the
rounded surface of the compound eye can have the same
axis, no two can transmit a ray of light from the very
same point of any object looked at ; while, as each of the
composite eyes is immovable, except as the whole head
moves, the combined action of the whole 24,000 lenses
insects: their ears and eyes. 1GD
can present to the sensorium but the idea of a single,
undistorted, unconfused object, probably on somewhat
of the same principle by which the convergence of the
rays of light entering our two eyes gives us but a single
stereoscopic picture.
The soft blue colour of this Dragon-fly's eyes,- — as also
the rich golden reflections seen on the eyes of other
insects, as the Whame-flies, and many other Diptera, —
is not produced by the pigment which I have alluded to,
but is a prismatic reflection from the corner.
You would suppose that, having 24,000 eyes, the
Dragon-fly was pretty well furnished with organs of
vision, and surely would need no more ; but you would
be mistaken. It has three other eyes of quite another
character.
If you look at the commissure or line of junction of
the two compound eyes on the summit of the head, you
will see, just in front of the point where they separate,
and their front outlines diverge, a minute crescent-shaped
cushion of a pale-green colour, at each angle of which is
a minute antenna. Close to the base of each antenna
there is set in the black skin of the head that divides
the green crescent from the compound eyes, a globose,,
polished knob of crystal-like substance, much like the
"bull's eyes " that are set in a ship's deck to enlighten
the side-cabins. On the front side of the cushion there
is a third similar glassy sphere, but much larger than the
two lateral ones. What are these?
They are eyes, in no important respect differing from
the individuals which comj)ose the compound masses,
except that they are isolated. The shining glassy sphere
is a cornea of hard transparent substance, behind which
is situated a spherical lens, lodged in a kind of cup
formed by an expansion of the optic nerve, and which
is surrounded by a coloured pigment-layer.
You may study these simple eyes, or stem mat a as they
170 EVENINGS AT THE MICROSCOPE.
are called, in many other insects, though they are not
so universally present as the compound eyes. On the
forehead of the Honey-bee they are well seen, as three
black shining globules, placed, as in the Dragon-fly, in a
triangle.
It is reasonable to presume that some difference, im-
portant to the insect, exists between the perceptions
obtained by means of the simple, and those obtained by
means of the compound, eyes ; but what is the nature of
the difference is certainly not known, and probably could
not be imagined by us, who know only one kind of
vision.
CRABS AND SHRIMPS. 171
CHAPTER XL
CRABS AND SHRIMPS.
It is always interesting to trace the varied forms and
•conditions under which any particular function is per-
formed ; and particularly to mark, in creatures very-
remote from us in the scale of being, the organs devoted
to the senses which are so requisite to our own comfort.
We have already seen some of these diversities in ex-
amples taken from the classes Mollusca and Insects;
and will now examine some more, as they appear in the
Crustacea.
If you look at the head of a Crab, a Lobster, or a
Prawn, you will see that it is furnished, like that of
Insects, with jointed antenna? ; but, whereas in insects
there is never more than a single pair, in the creatures
of which I am speaking there are two pairs. In the
Prawn you may suppose, at first sight, that there are
four pairs ; but that is because the internal antenna? ter-
minate each in three many-jointed bristles, in structure
and appearance exactly like the bristles of the outer pair,
two of the three being nearly as long as the outer, while
the third is short. In the Lobster, the internal are two-
bristled, both bristles rather short, while the external are
very long. In the Flat-crabs each pair is simple, the
inner minute, the outer long. In the great Eatable Crab
each pair is very small, and they are dissimilar.
Now, taking the last-named animal as the representa-
tive of his class, let us examine one of his inner antennae
first. It consists of a jointed stem and a terminating
bristle ; the latter furnished with small hairs common to
172 EVENINGS AT THE MICROSCOPE.
the general surface of the body, and with long, delicate,
membranous filaments (setce, often improperly called
cilia), which are larger and much more delicate in
structure than the ordinary hairs.
The basal joint is greatly enlarged : if it be carefully
removed from its connexion with the head, and broken
open, it will be found to inclose in its cavity a still smaller
chamber, with calcareous Avails of a much more delicate
character than the outer walls. This internal cell is con-
sidered by Mr. Spence Bate to be a cochlea* from its
analogy, both in structure and supposed use, to the organ
so named in the internal ear of man and other vertebrate
animals. It is situated, as has been said, in the cavity of
the basal joint of the internal antenna, and is attached to
the interior surface of its wall farthest from the median
line of the Crab. It has a tendency to a spiral form, but
does not pass beyond the limits of a single convolution.
If this interior cell does indeed represent the cochlea
of more highly-constructed ears, to which it bears some
resemblance both in form and structure, then it seems to
identify, beyond dispute, these inner or upper antennae
as the organs of hearing.
Now with this conclusion agrees well the manner in
which the living animal makes use of the organs in ques-
tion. The Crab always carries
them erectand elevated ; and is
incessantly striking the water
with them, with a very peculiar
jerking action, now and then
vibrating, and, as it has been
called, " twiddling " them.
These antennae, therefore, ap-
EAR OF CRAB PROM BEHIND. - . .
pear to be always on the watch :
* Cochlea, the Latin for Snail-shell, is the name given to one of
the en vi ties of the ear, from its resemblance to the interior of a snail-
shell.
CRABS AND SHRIMPS. 173
let the animal be at rest, let it be feeding, no matter, the
inner antennae are ever elevated, and on constant guard.
The lengthened and delicate seta? with which they are
furnished are, moreover, peculiarly adapted to receive and
convey the most minute vibratory sensations from the
medium in which they are suspended ; and, on the whole,
it seems to be satisfactorily settled by Mr. Spence Bate
(to whose excellent memoir* I am indebted for these
explanatory details) that the inner antennae are real ears.
Having thus taken our Crab by the ears, we will en-
deavour next to tweak his nose. But stay, we must
lind it first. We turn our horny gentleman up, and in
his Hat ancient face we certainly discern little sign of a
nasal organ. Our friend Mr. Bate must assist us again.
He will tell us to look at the outer or lower antenna-.
We will look, accordingly, magnifier in hand, while he
makes it clear to us that these are a pair of noses.
Each of these organs is formed of a stem, consisting
in general of five joints and a filament of many minute
joints. In the Prawn and the Lobster all the five joints
of the stem are distinct; but in the Crab the whole are, as
it were, soldered together into a compact mass, so that the
separate articulations are scarcely to be distinguished ;
while in some species their position can be indicated only
by the presence of the olfactory operculum or lid.
This important little organ varies in its construction in
the different families of Crustacea. In the Crab it is a
small movable appendage, situated at the point of junction
between the second and third joints ; it is attached to a
long calcareous lever-like tendon, at the extreme limit of
which is placed a set of muscles, by which it is opened
and closed ; to assist in which operation, at the angle of
the operculum most distant from the central line of the
animal are fixed two small hinges. When the operculum
* u
Annals of Xat. Hist." for July, 1S55.
174 EVENINGS AT THE MICROSCOPE.
is raised, the internal surface is found to be perforated!
by a circular opening protected by a thin membrane.
In the Prawn, Shrimp, and Lobster, there is no oper-
culum, but only the orifice covered by a membrane,
which is placed at the extremity of a small protuberance,
and is not capable of being withdrawn into the cavity of
the antennae, as in the Crab.
In the latter animal, the little door, when it is raised,
exposes the orifice in a direction pointing to the mouth ;
and where there is no door, still the direction of the open-
ing is the same, inwards and forwards, answering to the
position of the nostrils in the higher animals. In each
case it is so situated, that it is impossible for any food to
be conveyed into the mouth without passing under this
organ ; and there most conveniently the animal is enabled
to judge of the suitability of any substance for food, by
raising the little door and applying to the matter to be
tested the sensitive membrane of the internal orifice.
Thus it is concluded that this lower or outer pair of
antenna? are the proper organs of smell, as the upper
and inner are of hearing.*
The eyes, though constructed on the same general
principles as those of Insects, yet present some particulars
worthy of your notice. In the Crabs and Lobsters they
consist of numerous facets, behind each of which is a
conical or prismatic lens, the round extremity of which
is fitted into a transparent conical pit, corresponding to
a vitreous body, while the conical extremity of these
lenses is received into a kind of cup, formed by the
filaments of the optic nerve. Each of these filaments,
together with its cup, is surrounded by pigment matter,
in a sheath-like manner. To see this structure would
require anatomical skill ; but you may here examine
with a low power portions of the cornea, or glassy
exterior, of the eye of a Crab, and of a Lobster. In the
* Op. cit.
CRABS AND SHRIMPS. 175
former you see that the facets into which the cornea is
divided are hexagonal, like those of most Insects, but
in the latter they are square.
But Crustacea have a far greater faculty of circum-
spection than insects have; for besides the extensive
convexity and numerous facets of their eyes, these organs
are placed at the extremity of shelly foot-stalks, which
are themselves movable on hinges, capable of being-
projected at pleasure, and of being moved in different
directions, and of being packed snugly away, when not
in active use, in certain grooves hollowed out expressly
for them in the front margin of the shell.
We might find much more both instructive and amus-
ing in examining microscopically the structure of the
higher Crustacea ; but we will now dismiss them in order
to discuss some of the lower forms, many of which are
so minute that their whole bodies may be watched with
ease performing all the functions of life, while confined
under our eye, on the stage of the microscope. I refer
to the tiny active little creatures known as Water-fleas,
which are abundant in both fresh and salt water.
In this jar of fresh water, which has been standing in
the window for weeks, you may see among the green
filaments of Chara many little atoms, which scuttle
hither and thither with a rapid succession of short leaps.
These belong to the genus Cyclops, and are Crustacea,
belonging to the order Entomostraca.
By the aid of a glass tube which I stop at one end
with my finger, I will endeavour to catch one. It is no
easy matter, as you see, for the instant the end of the
tube is brought near to one, he takes the alarm and
leaps nimbly away before I can make the water rush in
by withdrawing my finger from the other end. But I
have one at length.
Here it is ; a living atom, not more than a sixteenth
of an inch in length, looking something like a pellucid
176 EVENINGS AT THE MICROSCOPE.
egg, furnished with long antennas, with five pairs of
branching feet, and a long tail terminating in bristles.
But its parts and organs must not be dismissed in this
•summary way ; we must look at them in detail.
And, first of all, in the very midst of its forehead, like
that obscene giant* after whom our tiny friend is named,
— it possesses a single eye that glares like a ruby. It
would need no vast beam of olive-wood, sharpened and
heated in the fire, and "twirled about" by the united
strength of five heroes, to "grind the pupil out;" for
though brilliant and mobile, it is far too minute to be
touched by the tip of the finest needle. Yet it is
elaborately constructed; for it consists of a number (not
very large) of simple eyes placed beneath a common
glassy cornea. Several muscle-bands are attached to this
compound organ of vision, and are arranged so as to
form a cone, of which the eye is the base ; these give the
eye a movement of rotation upon its centre, which may
be distinctly seen.
All the limbs, including both pairs of antenna*, two
pairs of foot-jaws, five pairs of feet, and a pair of tail-
lobes, are furnished, at each of their many joints, with
tufts of long hairs ; these appear to act the part of
paddles, as the active little animal strikes the water
vigorously with all its limbs, for the purpose of pro-
gression ; and also for the creation of currents in the
fluid ; which currents subserve a double object, — the
bringing constant supplies of water to be respired, and
floating atoms of food to be devoured.
In this individual, which is a female, the antenna? are
nearly equal in size throughout their length ; but, in the
male, the middle joints of the upper pair are remarkably
enlarged, forming a large swelling, followed by a sudden
contraction, the first part of which is hinged. All of the
true feet and the second pair of foot-jaws are divided
* Odyss. IX.
CRABS AND SHRIMPS. 1 i <
to the base into two equal branches, so that the animal
seems to possess no fewer than twenty-six limbs : each
of which being many-jointed, and each joint, as I have
observed, being set with delicately-plumose hairs, the
whole effect is most elegantly light and feathery.
On each side of the slender tail-like abdomen you see
an oval bag, connected with the body by an exceedingly
slender thread of communication, and tightly filled with
pellucid globose bodies. Like John Gilpin, of equestrian
fame, when
" He hung a bottle on each fide
To keep his balance true/'
our little natatory harlequin "carries weight." But these
bags are filled with eggs, a temporary provision for their
due and proper exposure to the water, while yet they are
protected from enemies. They are developed only at
certain seasons, when the eggs, having attained a given
amount of maturity in the ovary, are transferred through
the exceedingly slender tube into these sacs ; and are there
carried about by the mother until the young are hatched ;
when the curious receptacles, being no longer needed,
are thrown off, and speedily decay.
Here is a second form. It is named Lynceus, and is
nearly as common as the Cyclops in our stagnant pools.
Essentially its structure is the same ; but it has this pecu-
liarity, that its body is inclosed within a transparent shell,
which is thin and flattened sidewise, and through whose
walls all the movements and functions of its parts are
distinctly visible. The shell is broadly ovate in outline,
comes to a sharp edge all along one half of its circum-
ference, but is open all along the other; as if two watch-
glasses were soldered together, edge to edge, and then a
portion of the edges ground away, so as to leave a narrow
but long entrance. Through this narrow orifice the limbs
are protruded for locomotion ; and through it the sur-
N
178 EVENINGS AT THE MICROSCOPE.
rounding water finds its way in currents, bringing oxygen
to be respired and food to be devoured.
The translucent shell descends in front into a sharp
long beak, below which are seen the organs of the mouth,
two pairs of foot-jaws, beset with fine bristles. At the
origin of the beak is the eye, consisting, as we saw in the
Cyclops, of several lenses, enveloped in a common cornea,
the whole forming a movable orsfan of a blue-black hue.
Just behind this, at the very highest part of the shell,
is a little colourless bladder-like vesicle, which constantlv
maintains a rapidly alternate contraction and dilatation.
This is the heart, and this motion circulates the blood.
Below this, there is seen a great translucent irregular
mass of fle^h, evidently comprising many viscera, which
winds along from one end of the shell to the other, nearly
occupying its entire area. It is not in connexion with it at
the hinder part, as we see by its free movements there,
where it curves round, and, bending beneath, terminates
in a blunt tail, armed with two strong hooks, which can
at pleasure be thrust down through the narrow orifice of
the shell, and become partially straightened by being
forcibly thrown backward. This great central mass is
mainly occupied by the alimentary canal, in which food
in various stages of assimilation may at all times be seen,
and in which the interesting function of digestion can
be witnessed throughout, from the first seizure of the
atom and its mastication by the jaws, to the discharge of
the useless remains.
The individual before us does not carry at this time
eggs in the process of development ; but the deficiency
is supplied by a Daplinia which is playing about in the
same drop of water. Here you perceive, between the
arched outline of the shell and the sinuous outline of the
free soft body, an open space of some size, which con-
stitutes a receptacle, in which the eggs are deposited as
they are laid, and in which they remain not only until
CRABS AND SHRIMPS.
179
the little animals are hatched, but until they have
acquired a sufficient maturity to swim about and get
their independent living.
This receptacle, in which you may see five or six eggs,
is freely open to the surrounding water, which enters
the slit edge of the shell behind the tail. Perhaps you
wonder why the eggs are not washed out by the respira-
tory currents ; they are, in fact, maintained in their posi-
tion only by a slender tongue-like projection from the back
of the parent, which appears to have that special object.
When, however, the young are ready for freedom, the
DAPHNIA.
mother has but to depress her body a little more than
ordinary, when the door is opened, and the young easily
slip from the receptacle into the open water.
These tiny odd-looking sprawling things that you see
moving about by quick jerks in the same drop of water,
are the young recently hatched. They are quite unlike
their parent, having as yet no bivalve shell, no abdomen,
and only three pairs of limbs. The body is a transparent
plate, resembling the bowl of a spoon in form, but ending
in two points which carry pencils of bristles. The large
x 2
180 EVENINGS AT THE MICROSCOPE.
dark eye is conspicuous in front, and the six-jointed and
bristled limbs radiate from the centre, projecting stiffly
on all sides. The second and third pairs are seen to be
double, each giving off a branch, which is pencilled with
bristles like the principal stem.
We have not yet done with these tiny Water-fleas.
The sediment at the bottom of this jar of water is quite
alive with a host of nimble atoms, some of which you
may see crawling up the sides of the glass. They are
quite distinct from either of the kinds we have been
examining, not only in details of structure, which is
more identical, indeed, than it seems at first sight, but in
habit; for, whtreas they shoot to and fro through the
water with great force and rapidity, these can scarcely
swim at all ; or, if they do, it is with comparative slow-
ness and much apparent effort; though over the smooth
side of their glass dwelling, or upon the stems of water-
plants, they glide along with much ease and elegance by
the quick vibrations of their pencilled feet.
The form we are now contemplating is distinguished by
the name of Cypris, a genus which contains a good many
British species. It is more completely inclosed in a shell
than even the Lynceus ; and its envelope more truly
resembles the shell of a bivalve Mollusk, for the valves
are open for more than three-fourths of their circum-
ference ; while the portion of the back that is united is
sufficiently elastic to allow of some degree of expansion,
thus answering the purpose of a hinge.
ISTow look at the elegant little creature. Its most pro-
minent feature is its two pairs of antenna?, one projecting
forwards and curved upwards, the other downwards.
Both consist of several transparent joints, and are tipped
with long clear bristles; but the pencils which tip the
upper pair are specially graceful, being as long as the
whole shell, exceedingly slender, beautifully curved, and
so transparent that they seem formed of spun glass.
CRABS AND SHRIMPS.
181
Another peculiarity is, that there seems to be but one
pair of legs, which terminate each in a hooked spine.
You now and then see these awkwardly thrust out from
beneath the hinder part of the shell, but locomotion is
principally effected by the pencilled antennae. There is,
however, a second pair of legs, but these do not usually
make their appearance outside the shell, being curved
backwards to sustain the ovaries.
v\\
sJy
CTPRIS.
Early in the present century, an Irish naturalist, Dr. J.
Vaughan Thompson, announced a discovery, which, up-
setting conclusions previously received by all, caused no
little dissent and opposition, and gave rise to a lengthened
and wide-spread controversy. A very minute crustaceous
animal was known as inhabiting the open sea, to which
the name of Zoea had been given. It had sessile (i.e., not
stalked) eyes, and was remarkable for having a long spine
projecting from the face, and a similar one standing up
from the centre of the back. Another form was known,
which constituted the genus Megalopa ; in which the
body was broad, the eyes stalked, and the abdomen pro-
jecting behind. This was also small, but somewhat
larger than the preceding.
Xobody suspected that these were other than inde-
182 EVENINGS AT THE MICROSCOPE.
pendent forms of animal life, distinct from each other,
and equally distinct from every known genus of Crustacea
besides. It was supposed that no animal of this class
underwent metamorphosis, or that change of form in
different periods of life which distinguishes Insects ; but
that these creatures retained through life the general
shape, slightly modified by development of parts and
organs, which they each displayed when hatched from
the egg.
But these conclusions were quite set aside by the
brilliant discovery of Thompson, that Zoea and Megal-
opa were the same animal in different stages of existence ;
and that, moreover, both were but the early states of
well-known and familiar forms of larger Crustacea ; —
which therefore undergo a metamorphosis, as complete
as that by which the caterpillar changes to a chrysalis,
and the chrysalis to a butterfly, and in every essential
point parallel to it.
In the Cove of Cork this naturalist met with a con-
siderable number of Zoeas, which he kept in captivity.
Some of these passed into the Megalopa form, which in
turn changed to the most abundant of all our larger
Crustacea, the common Shore-crab (Carcinus mcenas).
" Thus, in its progress from the egg to its final develop-
ment, the Crab was proved to pass through two tem-
porary conditions, which had previously been regarded
as types, not of genera only, but of different families ;
and both strikingly dissimilar from the group to which,
in its perfect state, it belongs."
I have not myself examined the transformations of
this species ; but, as they have been well worked out,
and as the animal is so abundant everywhere on the
coast that you may easily verify what has been ob-
served, I will cite you the elaborate account of Mr.
R. Q. Couch, of Penzance, who has investigated the
subject with great skill, zeal, and success.
CRABS AND SHRIMPS.
183
Having procured some specimens of the Shore-crab
laden with eggs just ready for shedding, he goes on to
say, " These were transferred to captivity, placed in
separate basins, and supplied with sea-water ; and in
about sixteen hours I had the gratification of finding
large numbers of the creatures alluded to above, swim-
ming about with all the activity of young life. There
could be but little doubt that these creatures were the
young of the captive Crabs. In order, however, to
ZOEA OF SHOKE-CKAB.
secure accuracy of result, one of the Crabs was removed
to another vessel, and supplied with filtered water, that
all insects might be removed ; but, in about an hour, the
same creatures were observed swimming about as before.
To render the matter, if possible, still more certain, some
of the ova were opened and the embryos extracted ; but
shortly afterwards I had the pleasure of witnessing, be-
neath the microscope, the natural bursting and escape
of one precisely similar in form to those found so
abundantly in the water. Thus, theD, there is no doubt
that these grotesque-looking creatures are the young of
the Cavchms memos; but how different they are from
184 EVENINGS AT THE MICROSCOPE.
the adult needs hardly be pointed out any further than
by referring to the figure. When they first escape they
rarely exceed half a line in length. The body is ovoid,
the dorsal shield large and inflated ; on its upper edge
and about the middle is a long spine, curved posteriorly,
and rather longer than the diameter of the bodv, though
it varies in length in different specimens; it is hollow,
and the blood may be seen circulating through it. The
upper portion of the body is sap-green, and the lower
semi-transparent. The eyes are large, sessile, and situ-
ated in front, and the circumference of the pupil is
marked with radiating lines. The lower margin 0f the
shield is waved, and at its posterior and lateral margin
is a pair of natatory feet. The tail is extended, longer
than the diameter of the shield ; and is composed of
five equal annulations, besides the terminal one ; its
extremity is forked, and the external angles are long,
slender, pointed, and attached to the last annulation by
joints. Between the external angles and on each side of
the median line are three lesser spines, also attached to
the last ring by joints. Between the eyes, and from
near the edge of the shield, hangs a long, stout, and
somewhat compressed appendage, which, as the animal
moves, is reflexed posteriorly between the claws. Under
each eye is another appendage, shorter and slightly more
compressed. The claws are in three pairs ; each is com-
posed of three joints, and terminates in four long, slender,
hair-like appendages. These claws are generally bent on
the body, but stand in relief from it. If the animal be
viewed in front, the lower margin of the dorsal shield
will be found to be waved into three semi-circular fes-
toons, the two external of which are occupied by the
eyes, and between which the middle one intervenes ; the
general direction of the claws will be seen to be at right
angles to the body. As the young lies inclosed within
the membranes of the egg, the claws are folded on each
CRABS AND SHRIMPS.
185
other, and the tail is flexed on them so far as the margin
of the shield, and, if long enough, is reflected over the
front of the shield between the eyes. The dorsal spine
is bent backwards, and lies in contact with the dorsal
shield ; for the young, when it escapes from the egg, is
cmite soft, but it rapidly hardens and solidifies by the
deposition of calcareous matter in what may be called
its skin. The progress of this solidification may be very
beautifully observed by watching the circulation in the
SECOND STAGE OF SHORE-CBAB.
(Meijulopo.)
-dorsal spine. When the creature has just effected its
liberation from the egg, the blood-globules may be seen
-ascending to the apex; but, as the consolidation advances,
the circulation becomes more and more limited in its ex-
tent, and is finally confined to the base. These minute
creatures, in this early state of their existence, are
natatory, and wonderfully active. They are continually
swimming from one part of the vessel to the other ; and,
when observed free in their native pools, are, if possible,
18G EVENINGS AT THE MICROSCOPE.
even more active than when in confinement. Their
swimming is produced by continued flexions and exten-
sions of the tail, and by repeated beating motions of
their claws ; this, together with their grotesque-looking
forms, gives them a most extraordinary appearance when
under examination. As the shell becomes more solid
they get less active, and retire to the sand at the bottom
of the vessel, to cast their shells and acquire a new form.
They are exceedingly delicate, and require great care
and attention to carry them through the first stage ; for
unless the water be supplied very frequently, and in
great abundance, thev soon die.
" The second form of transmutation is equally as re-
markable as the first, and quite as distinct from the adult
animal. In the species now under consideration this
second transformation is marked by the disappearance of
the dorsal spine ; the shield becomes flatter and more
depressed, the anterior portion more horizontal and
pointed, the three festoons having disappeared. The
eyes, from being sessile, are now elevated on footstalks,
the infra-orbital appendages become apparently con-
verted into antenna?. The claws undergo an entire
revolution : the first pair become stouter than the others,
and are armed with a pair of nippers," the others being
simple ; " but the posterior pair are branched near the
base, and one of the branches ends in a bushy tuft. The
tail is greatly diminished in its relative size and propor-
tions, and is sometimes partially bent under the body,
but is more commonly extended. This form is as nata-
tory as the first. They are frequently found congregating
around floating sea-weed, the buoys and strings of the
crab-pot marks, and other floating substances, both near
the shore and in deep water. Their general form some-
what resembles a Galathea." *
Thus, under Mr. Couch's eye, the Zoea had changed to
* " Rep. Cornw. Polyt. Sec," 1843.
CRABS AND SHRIMPS.
18'
a Megalopa ; and this latter became, after a short time,
a Crab, in which were all the characters that belong to
the order to which the parent belongs ; but not those of
the genus nor even of the family. Its form bore a close
resemblance to that of the Sargasso Crabs (Gra-psidcr) ;
for the shield, instead of being large and arched in front,
and narrowed behind, was nearly square, while the front
was (taking in the eyes) almost straight, the lateral
angles much advanced.
THIRD STAGE OF SHOBE-CRAB.
(Grapsoid.)
This Crab, however, was still very minute : and many
sloughings were before it. In the course of these it was
destined gradually to attain, not only the dimensions of
its parents, but also their form. This, however, would be
matter of development rather than metamorphosis : the
lateral outlines of the shield would more and more ap-
proach each other behind, while the series of points that
now belonged to these lateral outlines would become
thrown into the front margin, which would by degrees
assume an arched form, as you may see in the figure of
the adult Crab.
Though I cannot at this moment show you specimens
of the Carcinas in its earlier stages, yet I have here a
good number of the Zoeas of one of those intermediate
form s which are the connecting links between the Crabs
and Lobsters : I mean Galathea. The adult animal is
188
EVENINGS AT THE MICROSCOPE.
of a broad squat form, something like what you might
suppose a Lobster to be, if it had been flattened between
two stones, without being actually destroyed. We have
two or three species, one of which is adorned with bril-
liant scarlet and azure paintings ; but I cannot tell to
which of them all this infant form belongs.
ADULT SHORE-CKAB.
You perceive that there is a general similarity between
these transparent little creatures and the Zoea described
1 »y Mr. Couch ; but there are great differences in detail.
The glassy shield or carapace shoots out in front in a stiff',
inflexible, very fragile spine. This is perfectly straight,
and nearly thrice the length of the whole shield. It is
beset, on various lines on its surface, with short slender
spmules jointed to shoulder-like angles, and not serratures.
Its interior is perforated by a canal which dilates and nar-
rows irregularly. The carapace posteriorly is semi-oval,
projecting a transparent convex vault over the part where
the abdomen is attached to it, as is seen when the latter
CRABS AND SHRIMPS. 189
Lends down. Its extremity gradually tapers into two
straight, sub-parallel, stiff spines, about as long as the
carapace itself, each terminating in a hooked point.
The abdomen ends in a spinous plate, which is very
elegantly lozenge-shaped and beset with spines. Each of
the two latero-posterior edges of the lozenge is cut into
six rectangular teeth, and each tooth bears on its hinder
face a long spine, articulated to it, and most delicately
plumose all along its sides. The hindmost pair of spines
are short, and are set close together, side by side. Be-
sides these jointed spines, each lateral angle of the
lozenge-shaped tail-plate projects into a spine-like tooth.
Though the individuals before us are all in the same
state as to the stage of their development, there is some
difference in size, indicating, doubtless, a corresponding-
diversity in age. "We will isolate a few of the largest and
put them into a glass trough for microscopical examination.
The largest, during the few minutes which I have
occupied in the process of dipping them out, has undergone
a metamorphosis. You observed that, after skipping about
the trough for a few minutes, it sank quietly to the bottom,
where it lay on its back; the next thing that you see is a
much more crab-like animal, more opaque, redder, much
larger, but lying on its back in the very spot where a
moment before you had seen a Zoea: while close by it
lies the transparent filmy skin which has been cast off.
The new animal is evidently now in its final state,
needing only development of its parts, which it would
obtain, if in freedom, by successive moults, to acquire
the adult form.
If we now submit the exuviae in detail to a power of 220
diameters, we shall obtain some interesting views of the
structure. The slough of the eyes in particular presents
one of the most exquisite objects that you can behold.
They are somewhat pear-shaped, with the facetted portion
well defined. It is the appearance of these facets, varying
190 EVENINGS AT THE MICROSCOPE.
according as the perfectly hexagonal outline of each,
or the smooth and glossy convexity, comes into focus,
that is so peculiarly charming.
Heturning now to the examination of one of the living
Zoeas, you perceive that the three pairs of pencilled
limbs do not represent any of the true legs; for the
transparency of the integuments allowing the interior
to be clearly seen, and the organs of the imago being
matured and just ready for sloughing, you discern, with
the most beautiful distinctness, the fingered claws (short
and stumpy, it is true, as compared with their perfect
form in the newly-freed imago) folded down upon the
breast within the skin, the second pair as large as these,
and traces of others beneath them, — all these forming
two great projecting lobes, slightly movable, beneath the
thorax of the Zoea, and occupying a bulk nearly equal
to that of the whole shield.
The circulation of the blood is beautifully clear. The
pellucid colourless globules chase each other by starts to
and fro, as the eye rests on the outgoing or returning
current. It is distinct in some parts where you would
scarcely have looked for it; as all over the lozenge plate
of the tail, in the interior of the eyes, throughout the
posterior spines of the shield, and the frontal spine. But
besides, and apparently independent of, the circulation,
there is a singular fusiform vessel in the latter segments
of the abdomen, penetrating the tail-plate, on the ventral
side. This vessel, now and then, at irregular intervals,
dilates quickly and closes; the wave proceeding upward
toward the head, but only for a short distance, and
unattended with any impulse to the blood-globules. The
nature of this vessel, and its use in the economy of the
infant Crab, I can in no wise explain.*
* For figures of these two forms the reader is referred to my Tenhy,
170, 172.
BARNACLES. ] 9 1
CHAPTER XII.
BARNACLES.
You cannot have wandered among the rocks on our
southern or western coasts, when the tide is out, without
having observed that their whole surface, up to a certain
level (often very precisely defined), is roughened with an
innumerable multitude of little brownish cones. If you
have ever thought it worth while to examine them with
more care, you have seen that, crowded as they are, so
thickly that frequently they crush each other out of their
proper form and proportions, they are all constructed on
the same model. Each cone is seen to be a little castle,
built up of stony plates that lean towards each other, but
which leave an orifice at the top. Within this opening,
provided the castle be tenanted by a living inhabitant, you
see two or three other pieces joined together in a peculiar
manner, which are capable of separating, but which, when
brought together, effectually close up all ingress.
Perhaps you have never pushed your investigations
farther than this, having a courteous respect for the feel-
ings of the inmate, which has prevented your intruding
on a privacy so secluded. But I have been less con-
siderate ; many a time have I applied the steel chisel
and hammer to the solid rock, and, having cut off some
projecting piece or angle, have transferred it, all covered
with its stony cones, to the interior of a glass tank of
sea-water, for more intimate acquaintance with the little
builders, at my leisure.
192 EVENINGS AT THE MICROSCOPE.
These are Barnacles (Balanidce). Such a colony I have
now in my possession, which I will submit to you ; for
they present a beautiful and highly interesting spectacle,
when engaged in their ordinary employment of fishing
for a subsistence. And not only so, but I have living
specimens of a much larger and liner species than the
common one, — the Belanus ])orcattis, whose castle stands
an inch or more in height. The structure, however, and
habits are pretty much the same in both.
Without disturbing the busy fishers, then, just take
vour seat in front of this tank, and, with a lens before
your eye, watch the colony which is seated on that piece
of stone, close to the glass side. From one and another,
every instant, a delicate hand is thrust forth, and presently
withdrawn. Fix your attention on some one conveniently
placed for observation. It is now closed ; but in a
moment, a slit opens in the valves within the general
orifice, displaying a black lining with pale blue edges; it
widens to an oval ; the pointed valves are projected, and
an apparatus of delicate curled filaments is thrust quickly
out, expanding and uncurling as it comes, to the form of a
fan; then in an instant more the tips of all the threads
again curl up, the threads collapse, and the whole appa-
ratus is quickly withdrawn, and disappears beneath the
closing valves. The next moment, however, they re-open :
and the little hand of delicate fingers makes another
grasp : and so the process is continually repeated while
this season of activity endures.
Now, by putting this specimen into a glass trough, and
placing it under a low power of the microscope, we shall
see what an exquisite piece of mechanism it is. The little
hand consists of twenty-four long fingers, of the most
delicate tenuity, each composed of a great number of
joints, and much resembling in this respect the antenna? of
a Beetle. These fingers surround the mouth, which is
placed at the bottom of the sort of imperfect funnel formed
BARNACLES.
193
by their divergence. They resolve themselves into six
pairs of arms ; for each one is branched from the basal
joint, dividing into two equal and consimilar portions.
Those nearest the mouth are the shortest ; and each pair
increases regularly in length to the most distant, which
are the central pair when the hand is extended. Each
division of each of this longest and most extensile pair
comprises, in the specimen before us, thirty-two joints,
while the shortest consists of about ten, the intermediate
ones being in proportion ; so that the whole apparatus
includes nearly live hundred distinct articulations; a
wonderful provision for flexibility, seeing that every
joint is worked by its own proper system of muscles.
Moreover, every separate joint is furnished with its
own system of spinous hairs, which are doubtless delicate
organs of touch, since it has been established that the
hairs with which the shelly coats of Crustacea are studded,
pass through the substance of the latter, and communicate
with a pulpy mass, richly sup-
plied with nerves, which lines
the shell.* These hair3 project V$P&
at a more or less wide angle
from the axis of the linger-like
filament, and are graduated in
length; and, what is very striking,
as illustrating the exquisite work-
manship of the Divine hand, the
hairs themselves are compound
structures ; for under a high
power they seem to be composed
of numerous joints, — a deceptive
appearance, probably, what look /$
like joints being rather successive . . / / v 'fl\
shoulders, or projections and con-
strictions of the outline, — while
HIND OF BABNACLE.
* "Pioc. Royal Society," ix. 215.
O
294 EVENINGS AT THE MICROSCOPE.
each shoulder carries a whorl of finer spines, lying nearly
close to the main hair, and scarcely deviating from its
general direction. This barbed structure of the hairs is
chiefly seen towards their attenuated extremities.
And now do you ask, — What is the object of this
elaborate contrivance, or rather series of contrivances 1
I answer, — It is the net with which the fisher takes his
food : it is his means of living. You have seen that the
animal has no power of pursuing prey : he is immovably
fixed to the walls of his castle, which is immovably
fixed to the solid rock. He is compelled therefore to
subsist on what passes his castle, and on what he can
catch as he sits in his doorway, and casts his net at
random.
You saw, also, with what a regular perseverance the
casts were made ; and now that you have examined in
detail the construction of the net, you are prepared to
appreciate its fitness for the work assigned to it. Its
extreme flexibility, produced by the number of its joints,
enables the fingers of the hand, or the threads of the net
(which you will), to stretch out and to curl up alter-
nately, while the number of the spreading fingers enables
the animal to grasp a comparatively large bulk of water
in those curling organs. These, then, form a sieve ; the
water passes through the interstices of the fingers, while
the tiny atoms of solid matter, or the equally minute
animalcules that constitute the food of the Barnacle, are
sifted out, and detained by the fingers, which, curling
inward, carry whatever is captured to the mouth.
But see how greatly the perfection of the instrument
is promoted by the projecting hairs with which every one
of the numerous joints is beset. These, standing out at
right angles (or nearly so) to the direction of the finger,
meet their fellows from the joints of the next finger,
and, crossing their points, fill the interstices with an
innumerable series of finer meshes, — meshes of such
BARNACLES. 195
delicacy that it is next to impossible that any organised
body inclosed in the given area should escape.
But there is more in them than merely this minute and
wide-spread ramification. They are, as we have seen,
organs of touch ; so that the net has not only the mecha-
nical power of capture, common to an inanimate cast-net
which a human fisher uses, but is endowed with the most
exquisite sensibility in every part. The slightest contact
of an animalcule in the inclosed water with one of those
thousands of sensitive hairs communicates instantly an
impression to the sensorium, and a consciousness of the
fact to the Barnacle ; who is thus, without doubt, able
with the quickness of thought to close the fingers together
.at that part, and thus secure the victim.
To make use of the prey thus secured, the Barnacle is
furnished with a mouth, which can be protruded into a
sort of wart, and is provided with a distinct lip bearing
minute palpi, and three pairs of jaws, of which the outer
two are horny and toothed, while the innermost is soft
and fleshy.
Fixed and immovable as the Barnacles are in their
adult and final stage, they have passed by metamorphosis
through conditions of life in which they were active,
roving little creatures, endowed with the power of
swimming freely in the wide sea. In this condition they
present the closest resemblance to familiar forms of
Crustacea, as you will perceive when you examine some
specimens of the larvae that I am able to show you.
I have in one of my tanks an individual of the fine
and large Barnacle, Balanus i^orcatus, which, for several
days past, has been at intervals throwing out from the
orifice of its shells dense clouds of atoms, which form
compact columns reaching from the animal to the surface
of the water. One of these cloudy columns, when ex-
amined with a lens, is seen to be composed of thousands
of dancing creatures, resembling the Water-fleas that
o 2
196 EVENINGS AT THE MICROSCOPE.
we lately examined. They maintain a vivacious motion,,
and yet at the same time keep their association and the
general form of the column.
Taking out a few of the dancing atoms, and isolating
them in this glass stage-cell, we see that they have exactly
the figure, appearance, and character of the young of the
common Cyclops ; so that you would, without hesitation,
if you knew nothing of their parentage, assign them to
that well-known genus. Their movements are almost
incessant ; a series of jerking progressions, performed
by quick but apparently laborious flappings of the limbs,
right and left together. They occasionally rest from
their exertions for a few moments, but seem to have no-
power of alighting on any object.
But, in order to obtain a more precise idea of the
structure of this tiny creature, we must manage to re-
strain its liberty a little, by applying gentle pressure
with the compressorium ; just sufficient to confine it
without hurting it. The body is inclosed in a broad
carapace, shaped much like a heraldic shield, but very
convex on the back, and terminating behind in a slender
point or spine, which is cut into minute teeth along the
edges. Below this shield is seen the body, with three
pairs of legs, a great proboscis in the middle pointing
downwards and backwards, and the anal fork, which
consists of a bulbous base and two diverging points^
which project behind under the spine of the shield.
The legs are exclusively swimming organs: they have
no provision for grasping, no claws or hooks, nor do they
appear to be capable of being used for crawling on the
ground, or for climbing among the sea- weeds. They are
fringed along one edge with long and stout, but somewhat
flexible, spines, of which those that are nearest the trunk
seem more rigid, and are directed more at right angles to
the limb, than the rest. The legs are formed of many
imperfect joints, and the second and third pairs are-
BARNACLES.
197
-double from the basal joint outwards, while the first
pair are simple. In the fore part of the body a large eye
is placed, deep-seated, which is of a roundish form, and
is intensely black both by reflected and transmitted light.
On the summit of the forehead are placed a pair of thick
flexible horn-like organs, which are abruptly bent in the
middle, and which I believe represent the first pair of
antenna?. This, then, is the first stage of the Barnacle —
the form under which it appears when it is hatched
from the egg.
YOUNG OF BAEXACLE.
Among the multitudes which have been evolved
•during these last few days, and which are now swimming
at large in the tank, we may be able to detect some
that have passed through their first stage, and, having
moulted their skin, have attained a more advanced form.
Here is one, which by its superior size seems to have
made some progress towards maturity.
Yes, here are more. These are evidently in their second
stage. There is an increase in length ; for, whereas the
198 EVENINGS AT THE MICROSCOPE.
former was only — J-yth of an inch in length, these have
attained to a length of T\jth of an inch. Yet this increase
is observable in no other dimension than that of total
length ; and this is due to the development of the terminal
spine of the shield, which is now much produced, and cut
into minute teeth. The anal fork is also attenuated,
lengthened, and bent abruptly downward at the base,
where it is very mobile; another bend in the middle
throwing the extremity into the horizontal again. The
delicately membranous pouch-like proboscis is more
clearly seen beneath the breast, the extremity of which
is directed backwards. In front of this organ there are
two decurved very mobile bristles, set on pedicles, or
stalks, the whole closely resembling the internal antennae
in the higher Crustacea. The lateral horns or external
antenna? appear to terminate in a very delicate brush of
hairs, which does not seem to be capable of being
protruded.
The little animals in this state swim, generally, back
downward ; though they frequently assume a perpen-
dicular position, both direct and reversed. I see them
now occasionally resting on sea- weeds and Diatomacece,
though the limbs seem even worse fitted than before for
crawling, since the spines or bristles with which they
are fringed are much increased in length, especially on
the third pair.
A specimen nearly twice as large as these last affords
us an opportunity of tracing the Barnacle to another point
of its transformations. The modifications are chiefly in
the proboscis and the anal fork. The former now points
directly downwards ; is furnished with a pair of minute
spines on its anterior side, and with a terminal hook ;
while its posterior side is set with strong vibrating cilia.
The anal fork is greatly increased in dimensions, has its
edges armed with spines articulated to its surface, and is
marked with longitudinal lines which resemble corruga-
*&'
BARNACLES. 199
tions. The under-surface of the body is also muck
corrugated transversely.
In the first moult the spine of the shield was greatly
increased, the size of the body itself remaining stationary;
in the second moult the ratio is reversed, the body has
largely increased, but the spine is nearly unchanged.
We cannot follow the metamorphosis any farther by
personal observations ; but from the researches of others,
and especially of Mr. Darwin, we know that other stages
have to be passed before the final fixed condition is
attained. As yet no perceptible advance has been made,
by either of the two moultings which we have traced,
from the free, jerking, dancing Water-flea that was first
hatched, towTards the sessile Barnacle inclosed in its
shelly cone of several valves, and firmly fixed to the
solid rock ; and we are yet at a loss to imagine how such
a change can be effected.
Nor is the matter apparently helped by the next moult;
for, though there now ensues a great change of form, it
does not seem to resemble the adult Barnacle much (if
at all) more than before. If described without reference
to its parentage, it would still be considered an Ento-
mostracous* Crustacean, or Water-flea, but removed to
another tribe. It represents, in fact, a Ci/pris/f the
body with its fringed limbs being now included within
two convex valves, like those of a mussel or other bivalve
shell, either united by a hinge along the back, or rather
soldered together there, so as only to allow a slight
opening and closing, by the elasticity of their substance.
The fore part of the head is now greatly enlarged, as are
also the antenna', which project from the shell. The
* From two Greek words — iprofior (entomos), cat up, and oarpaKov
(ostrakon), a shell. A term applied to a group of the Crustacean*
with minute bodies very much divided and inclosed in a shellv
covering.
+ See figure on p. 181.
200 EVENINGS AT THE MICROSCOPE.
single eye is separated into two, which are large and
attached to the outer arms of two bent processes placed
within the body, in the form of the letters UU. The
legs are increased by the addition of two pairs, and
these are doubly bent in a zig-zag form, and can be
protruded from between the valves.
It is a highly curious fact that the infant Barnacle has
thus passed through two distinct types of animal life,
those of the Cyclops and the Cypris. These are not one
type in different stages, as might be reasonably presumed.
The young of Daphnia and of Cyclops are so much alike,
that it would be natural to presume the young of Cypris
to be of the same form ; in which case, we should have
in the young Barnacle merely the first and second stages
of Cypris. But it is not so. Cypris does not pass
through the Cyclops form at all ; for, according to
Jurine, the young when hatched have the appearance of
the perfect animal, though varying a little in the shape
of their shells.
It is in this second form, which may be considered the
pupa of the Barnacle, that the animal quits its free, roving
life, and becomes a fixture for the remainder of its days.
And this is a most wonderful process: so wonderful, that
it would be utterly incredible, but that the researches of
Mr. Darwin have proved it incontestably to be the means
by which the wisdom of God has ordained that the little
Water-flea should be transformed into a stony Acorn
Barnacle.
Having selected a suitable place for fixing its re.-idence,
such as those massive rocks which sustain the impetuous
billows on our sea-worn coasts, the great projecting
antenna? manifest a new and unprecedented function.
Glands situated at their base secrete a tenacious <:lue,
which, being poured out in great profusion, cements the
whole front of the head to the rock, including and con-
cealing the antennae themselves. The cement rapidly
BARNACLES. 201
sets under water, and the animal is henceforth im-
movable.
It now moults its skin once more. Another great
change takes place; the bivalve shell is thrown off, as are
also the eyes with their bent supports, and it is seen to
be a true Barnacle, though as yet of minute dimensions,
and with its valves in a very rudimentary condition.
It is now the representative of a third type among the
Crustacean forms, for it is in effect a Stomapod;* such
as the Opossum Shrimp (Jfysis), for example, with the
shield composed of several pieces, stony in texture, on
account of the great development of their calcareous
element, and so modified in form as to make a low cone,
the legs (become the cirri, or what I have above called
the "fingers") made to perform their movements back-
wards instead of forwards, and the whole abdomen
reduced to an almost invisible point.
Marvellous indeed are these facts. If such changes
as these, or anything approaching to them, took place in
the history of some familiar domestic animal, — if the
horse, for instance, were invariably born under the form
of a fish, passed through several modifications of this
form, imitating the shape of the perch, then the pike,
then the eel, by successive castings of its skin ; then by
another shift appeared as a bird ; and then, glueing
itself by its forehead to some stone, with its feet in the
air, threw off its covering once mote, and became a foal,
which then gradually grew into a horse; — or if some
veracious traveller, some Livingstone or Earth, were to
tell us that such processes were the invariable conditions
under which some beast of burden, largely used in the
centre of Africa, passed, — should we not think them
very wonderful 1 Yet they would not be a whit more
* From the Greek aro\ia (stoma'), mouth, and ttovc (pons), foot. A
name given to those Crustaceans which have proper feet near the
mouth.
202 EVENINGS AT THE MICROSCOPE.
wonderful, in this supposed case, than in the case of the
Barnacle, in whose history they are constantly exhibited
in millions of individuals, and have been for ages ; even
in creatures so common that we cannot take a walk
beneath our sea-cliffs, without treading on them by
hundreds !
SPIDERS AND MITES. 203
CHAPTER XIII.
SPIDERS AND MITES.
Spiders, I am sure, are not favourites with you. With
the exception of the poor prisoner in the Bastille, who
had succeeded in taming a Spider, — the only creature
besides himself that inhabited his dungeon, — I do not
think I have ever heard of any one who loved or admired
Spiders morally. Yet, physically, we may find much to
admire in them, as net a few naturalists have done before
us ; there are men who have devoted their lives to the
study of this unamiable race, and who have discovered
in them the same wondrous skill, and the same perfect
adaptation of organ to function, of structure to habit,
that mark all God's works, whether we think them pretty
or ugly, amiable or repulsive.
I am going to show you some of these pieces of mechan-
ism. Remember that the whole tribe is sent into the
world to perforin one business: they are commissioned
to keep down what would otherwise be a " plague of flies."
They are fly-butchers by profession • and, just as our
beef and mutton-butchers have their slaughter-house,
their steel, their knives, their pole-axe, their hooks, so
are these little slaughterers furnished with nets and
traps, with caves, with fangs, and hooks, and poison-
bags, ready for their constant work. They have, in fact,
nothing else to do : their whole lives are spent in
slaughtering, — with the exception of rearing fresh gene-
rations of slaughterers,— and I suppose they think, and
are intended to think, of nothing else.
204 EVENINGS AT THE MICROSCOPE.
I was one day in an omnibus, in the corner of which
sat a butcher. Presently a man got in, whose blue ging-
ham coat indicated the same trade. He seated himself
opposite the other, and the two were soon in conversation.
*'Do you know Jackson?" says A. "No," savs B:
" where does he slaughter?" The reply gave me a new
idea; he evidently considered that "slaughtering" was
the only occupation worthy of a man, and therefore the
only one worthy of man's thought. Spiders are just the
same. If an Epeira met a Clubiona, probably the first
interchange of civilities would be something like —
"Where do you slaughter?"
" No one," says Professor Rymer Jones, " who looks at
the armature of a Spider's jaws can mistake the intention
with which this terrible apparatus was planned. 'Murder '
is engraved legibly on every piece that enters into its com-
position." But surely the Professor is rather severe. I
do not think this paragraph was written on an autumn
morning, when the flies had driven him out of bed prema-
turely early, by incessantly alighting on his nose ; nor on
coming home from a summer evening's walk through the
marsh, where clouds of singing and stinging gnats had
been the only objects of cognisance to sight, hearing, and
feeling. If so, he would have been ready to pronounce
" killing no murder," and have blessed the slaughtering
Spiders as pursuing a most praiseworthy and useful
occupation. Circumstances change opinions.
We will not, then, touch the moral question; but just
look at this apparatus from the head of one of our common
Spiders (Clubiona atrox), a long-legged and swift species,
that builds a compact cloth-like web in our out-houses,
with a gallery open at each end for retreat in danger.
The specimen is a part of the slough or cast skin, which
you may always find in the neighbourhood of such a web ;
-■and it is particularly suitable for examination, because it
is sloughed in the most perfect condition ; every part, the
SPIDERS AND MITES. 205
fangs, the palps, the legs, with all their joints, the corneae
of the eyes, the entire skin with every hair, — all are here,
and all in their places, with a cleanness and translucency
which it would require much skill in dissection to obtain,
if we captured a living Spider for our purpose.
There are in front of the head two stout brown organs,
which are the representatives of the antennae in insects;;
though very much modified both in form and function.
They are here the effective weapons of attack. Each
consists of two joints : the basal one, which forms the
most conspicuous portion of the organ, and the terminal
one, which is the fang. The former is a thick hollow case,
somewhat cylindrical, but flattened sidewise, formed of
stiff chitine, covered with minute transverse ridges on its
whole surface, like the marks left on the sand by the
rippling wavelets, and studded with stout coarse black
hair. Its extremity is cut off obliquely, and forms a
furrow, the edges of which are beset with polished conical
points, resembling teeth.
To the upper end of this furrowed case is fixed by a
hinge-joint the fang, which is a curved claw-like organ,
formed of hard chitine, and consisting of two parts, a
swollen oval base, which is highly polished, and a more
slender tip, the surface of which has a silky lustre, from
being covered with very fine and close-set longitudinal
grooves. This whole organ falls into the furrow of the
basal joint, when not in use, exactly as the blade of a
clasp-knife shuts into the haft ; but, when the animal is
excited, either to defend itself or to attack its prey, the
fang becomes stiffly erected.
By turning the object on its axis, and examining the
extreme tip of the fang, we see that it is not brought to a
fine point, but that it has the appearance of having been
cut off slant-wise just at the tip ; and that it is tubular.
Now this is a provision for the speedy infliction of death
upon the victim ; for both the fang and the thick basal
20G EVENINGS AT THE MICROSCOPE.
joint are permeated by a slender membranous tube,
which is the poison duct, and which terminates at the
open extremity of the former, while at the other end it
communicates with a lengthened oval sac, where the
venom is secreted. This, of course, we do not see here,
for it is not sloughed with the exuvise, but retained in
the interior of the body ; but in life it is a sac, extending
into the cephalo-thorax, — as that part of the body which
carries the legs is called, — and covered with spiral folds
produced by the arrangement of the fibres of its con-
tractile tissue.
When the Spider attacks a fly, it plunges into its
victim the two fangs, the action of which is downwards,
and not, like that of the jaws of insects, from right to left.
At the same instant a drop of poison is secreted in each
gland, which, oozing through the duct, escapes from the
perforated end of the
fang into the wound, and
rapidly produces death.
The fangs are then clasp-
ed down, carrying the
prey, which they power-
fully press against the
FANG OP SPIDER. j.1 1 1 p j 1
toothed edges or the stout
basal piece, by which means the nutritive fluids of the
prey are pressed out, and taken into the mouth, the
dried and empty skin being rejected. The poison is of
an acid nature, as experiments performed with irritated
spiders prove; litmus paper pierced by them becoming red
as far round the perforations as the emitted fluid spreads.
In the slough, the upper surface of the cephalo-thorax
is always detached as a thin plate, convex outwardly, con-
cave inwardly. As it is upon the front portion of this
division of the body that the eyes are situate, the slough
displays these with great clearness and beauty beneath the
microscope. Here you may see them. The whole slough
SPIDERS AND MITES. 207
from its thinness is semi-pellucid, but the eyes transmit
the light with brilliance, not, however, as if they were
simple round holes, because you can discern very mani-
festly a hemispherical glassy coat, by which it is refracted.
It is, however, when we examine the forehead of a
living Or recently killed spider, that we see the eyes to
advantage. In this example of the same species (Clubiona
atrox), you see them, like polished globes of diamond,
sunk into the solid skin of the head. Their form is
unimpeachably perfect, and the reflection of light from
their surface most brilliant.
EYES OF SPIDEB.
The arrangement of these lustrous eyes is worthy of
attention. They are generally eight in number in Spiders ;
but their relative position varies so much, as to afford
good characters by which naturalists have grouped them
in genera. In the Clubiona which we have been examin-
ing, they are placed in two nearly straight transverse rows
on the forehead ; but, as this surface is convex, it follows
that the axis of every' eye points in a different direction
from that of its fellows. In Epeira, on the other hand,
represented by our Great Garden Spider, so commonly
208 EVENINGS AT THE MICROSCOPE.
seen in the centre of its perpendicular web, on shrubs
and in corners of our gardens, the four middle eyes
form a square, and the two lateral ones on each side are
placed in contact with each other.
It is interesting to remark that their arrangement is not
arbitrary, but is ancillary to the varying instincts and
wants of the different kinds. On this subject I will quote
to you what Professor Owen says : — "The position of
the four median ones is the most constant ; they gene-
rally indicate a square or trapezium, and may be com-
pared with the median ocelli in hexapod insects. The
two, or the two pairs of lateral ocelli may be compared
with the compound eyes of insects ; the anterior of these
lias usually a downward aspect, whilst the posterior looks
backwards; the variety in the arrangement of the ocelli of
Spiders always bears a constant relation to the general
ronformation and habits of the species. Dujrs has
observed that those Spiders which hide in tubes, or lurk
in obscure retreats, either underground or in the holes or
fissures of walls or rocks, from which they only emerge to
seize a passing prey, have their eyes aggregated in a close
group in the middle of the forehead, as in the Bird-spider,
the Clotho, &c. The Spiders which inhabit short tubes,
terminated by a large web exposed to the open air, have
the eyes separated, and more spread upon the front of the
cephalo-thorax. Those Spiders which rest in the centre
of a free web, and along which they frequently traverse,
have the eyes supported on slight prominences which
permit a greater divergence of their axes : this structure
is well marked in the genus Thomisa, the species of
which lie in ambuscade in flowers. Lastly, the spiders
called Errantes, or wanderers, have their eyes still more
scattered, the lateral ones being placed at the margins
of the cephalo-thorax." *
The shining hemisphere (or nearly a sphere) is in each
* " Comp. Anat." (Ed. 2), 451.
SPIDERS AND MITES. 209
case covered with a thick cornea, a continuation of the skin,
perfectly transparent, and throwing off its outer coats
successively in the process of moulting, like that of the
rest of the body. The centre of its inner surface is deeply
excavated for the reception of a crystalline lens, which is
globular in form, and which rests behind on the front sur-
face of a hemispherical vitreous body, without sinking into
it. The space between this body and the sides of the lens
forms a ring-like channel which is filled with an aqueous
humour, and into this projects a circular process of the
thick pigment-coat, which corresponds to the choroid, thus
defining the pupil of the eye, and at the same time con-
fining the lens to its proper situation. The margin of this
pigment-ring may be considered as an iris, and is of
various colours, as red, green, or brown, in those species
which are active by daylight, while it is black at the back
of the eye. The nocturnal species have no dark pigments,
but are furnished with a curtain (tapetum), which reflects
a brilliant metallic lustre, and makes the eves of these
Spiders glare in the twilight, like those of cats.
It will be interesting to compare with this range cf
eyes, the same organs in a kindred animal, the common
Harvestman (Phalanghnn cornutum). Here in the centre
of the cephalo-thorax rises a short pillar, which is
crowned with two rows of conical points, with polished
black tips. On each side of the pillar is a large black eye,
hemispherical in form and brilliantly glossy, exactly re-
sembling, indeed, those which we have just examined.
There are, however, only this single pair which thus look
out laterally, exactly like the eyes of Birds. There is,
indeed, a speck on each side of the thorax, considerably
removed from the eye-pillar, just above the origin of the
first pair of legs, which has been mistaken for an eye ;
'but it is truly a spiracle, or breathing-hole.
There are many other points of interest about this Har-
vestman, such as the conical spines which stud the head,
p
210 EVENINGS AT THE MICROSCOPE.
body, and limbs ; the multitude of small bead-like joints
into which the foot (tarsus) is divided : and in particular
the hammer-like form of the modified antenme, which
bend abruptly downwards, and have pincer-tips. These
are highly curious, and you may examine them at your lei-
sure ; but for the present we will return to our Spiders.
Ever since those mythic times when Arachne contended
with Minerva for supremacy in needlework, and was
changed, for her pains, into a spider, our little spinners
have been famous (Spider = ^m\\z) for their matchless
achievements in thread. And still their industrious art
is plied everywhere around us ; in our chambers, in our
windows, in our cellars, in our walls, in our gardens, in
waste and desert places, and even under water. But you
shall hear what Professor Owen says on the degree and
mode in which Spiders exercise their singular secreting
faculty, which " varies considerably in the different
species. Some, as the Clubionce, line with silk a conical or
cylindrical retreat, formed, perhaps, of a coiled-up leaf,
and having an outlet at both extremities, from one of
which may issue threads to entrap their prey. Others,
as the Segestrice, fabricate a silken burrow of five or six
inches in length, in the cleft of an old wall. The Mygale
cemetaria lines a subterraneous burrow with the same
substance, and manufactures a close-fitting trap-door of
cemented earth, lined with silk and so attached to the
entry of the burrow as to fall down and cover it by its
own weight, and which the inmate can keep close shut
by means of strong attached threads.
" The arrangement of Spiders by Mr. Walckenaer into
families, characterised by their habits, places the principal
varieties of their webs in a very concise point of view.
" The Cursores, Saltatores, and Laterigradw make no
webs : the first catch their prey by swift pursuit ; the
second spring upon their prey by insidious and agile-
leaps ; the third run, crab-like, sideways or backwards,
SPIDERS AND MITES. 211
and occasionally throw out adhesive threads to entrap
their prey. The Latebricolce lijde in burrows and fissures,
which they line with a web. The Tubicolce inclose them-
selves in a silken tube, strengthened externally by leaves
or other foreign substances. The XiditeJce weave a nest,
whence issue threads to entrap their prey. The Filitelcp,
are remarkable for the long threads of silk which they
spread about in the places where they prowl in quest of
prey. The Lapitelce spin great webs of a close texture,
like hammocks, and wait for the insects that may be
entangled therein. The Orbitelce spread abroad webs
of a regular and open texture, either circular or spiral,
and remain in the middle or on one side, in readiness to
spring upon an entangled insect. The RetiteliP spin webs
of an open mesh- work, and of an irregular form, and
remain in the middle or on one side, to seize their prey.
Lastly, the Aquitelce spread their silken filaments under
water, to entrap aquatic insects.
" The silken secretion of Spiders is not applied only to
the formation of a warm and comfortable dwelling for
themselves, or of a trap for their prey ; it is often em-
ployed to master the struggles of a resisting insect, which
is bound round by an extemporary filament, spun for the
occasion, as by a strong cord. It forms the aeronautic
filament of the young migratory brood. It serves to
attach the moulting Hydrachna to an aquatic plant by
the anterior part of the body, when it struggles to with-
draw itself from its exuvium. Lastlv, a softer and more
silken kind of web is prepared for the purpose of re-
ceiving the eggs, and to serve as a nest for the young." *
The silk with which these various fabrics are con-
structed is a thick, viscous, transparent liquid, much like
a solution of gum arabic, which hardens quickly on expo-
sure to the air, but can meanwhile be drawn out into
thread. So far, it agrees with the silk of the silkworm
* Owen, "Comp. Anat." (Ed. 2), 458.
p 2
212 EVENINGS AT THE MICROSCOPE.
and other caterpillars ; but the apparatus by which it is
secreted, and that by which it is spun, are both far more
complex and elaborate than those of the latter. Generally
speaking, there are three pairs of spinnerets, or external
organs, through which the threads are produced ; but in
some few cases there are only two pairs," and in others,
as the Garden Spiders (Epeira), the hindmost pair seem
to be united into a single spinneret. These are always
situated at the hinder extremity of the body, and I will
show them to you presently. First, however, I will de-
scribe the internal apparatus ; the source of the threads.
The glands which secrete the gummy fluid are placed
in the midst of the abdominal viscera ; and, in some in-
stances— as in the female of Epeira fasciata, a species
which makes a remarkably large web — they occupy
about a quarter of the whole bulk of the abdomen.
About five different kinds of these glands mav be dis-
tinguished, though they are not all present in every
species. The Epeircr, however, present them all.
In this genus there are : — 1. Small, pear-shaped bags,
associated in groups of hundreds, and leading off by
short tubes, which are interlaced in a screw-like manner,
and open in all of the spinnerets. 2. Six long twisted
tubes, which gradually enlarge into as many pouches, and
then are each protracted into a very long duct, which
forms a double loop. 3. Three pairs of glandular tubes,
similar to the preceding, but which open externally
through short ducts. 4. Two groups of much-branched
sacs, whose long ducts run to the upper pair of spinnerets.
5. Two slightly-branched blind tubes, which terminate
by two short ducts in the middle pair of spinnerets, f
It is not very easy to examine the spinnerets with a
* "There is a fourth pair in Mr. Blackwall's family of the Cini-
floridce, situate iu front of the ordinary anterior pair." (Meade.)
T See a valuable account, by Mr. E. H. Meade, of the secreting
glands in Spiders, and of the distinct functions of the various kinds of
these organs, read at the British Association, Sept. 25, 1S58.
SPIDERS AXD MITES. 213
microscope, so as to make out their structure. If we
confine the Spider in a glass cell, it is so restless that the
least shock or change of position will cause it to move to
and fro ; and, besides, when it does become quiescent,
the spinnerets are closed in towards each other, so that
we cannot see their extremities. By selecting a speci-
men, however, recently killed, such as this Clubiona, we
may discern sufficient to enable us to comprehend their
construction.
Looking, then, at the abdomen from beneath, we see
the three pairs of spinnerets clustered together close to
the extremity. The pair most forward are shaped some-
what like barrels, whose free ends bend over toward each
other. They are covered with stiff black hairs, and just
within the margin of what may be called the head of the
barrel (for it is cut off horizontally, with a sharp rioi),
there is a circle of very close-set, stiff, whitish bristles,
which arch inwards. The whole flat surface of the
" head," within this circle of bristles, is beset with very
minute horny tubes, standing erect, which are the
outlets of the silk-ducts that belong to this pair.
Behind this first pair are seen the middle pair, almost
concealed, however, from their shortness and smallness,
and from the approximation of the first and third pairs.
We can discern that thev are more teat-like than the
preceding, terminating in a minute wart, which is pro-
longed into a horny tube. The whole teat is set with
similar tubes, which are larger and longer than those of
the first pair. Finally, the third pair resemble palpi, for
each consists of two lengthened joints, and are bluntly
pointed. The spinning tubes in these are limited, as it
appears to me, to one or two at the extreme end of each
spinneret, the whole surface besides being covered with
the ordinary long bristles. Strictly speaking, however,,
they are three-jointed, for all the spinnerets spring from
wart-like sockets, which may be considered as basal
.214 EVENINGS AT THE MICROSCOPE.
joints ; and as the circlet of bristles in the first pair
doubtless indicates a short joint, sunken as it were
within the preceding, this pair is likewise three-jointed ;
the middle pair appears to be but two-jointed.
The minute horny tubes are themselves composed of
two joints, the basal one thick, the terminal one very-
slender, and perforated with a very minute orifice, through
which the gum oozes at the will of the animal as an
equally attenuated thread. On our Clubiona, the number
of tubes in all the spinnerets is about three hundred; but
in the Garden Spider (Epeird) they exceed a thousand.
This remarkable multiplicity of the strands with
which the apparently simple and certainly slender thread
of the Spider is composed, has attracted the attention of
those philosophers wrho seek to discover the reasons of
the phenomena they see in nature. The explanation
was first suggested, I believe, by Mr. Itennie,* but it
has been amplified with much force by Professor Jones,
in the following words : —
" A very obvious reflection will here naturally suggest
itself in connexion with this beautiful machinery ; why,
in the case of the Spider, it has been found necessary to
provide a rope of such complex structure, when in so
many Insects a simple, undivided thread, drawn from the
orifice of a single tube, like the thread of the silkworm,
for instance, was sufficient for all required purposes. And
here, as in every other case, it will be found on considera-
tion, that a complicated apparatus has been substituted
for a simple one only to meet the requirements of strict
necessity. The slow-moving caterpillar, as it leisurely
produces its silken cord, gives time enough for the fluid
©f which it is formed to harden by degrees into a tenacious
filament, as it is allowed to issue by instalments from the
end of the labial pipe ; but the habits of the Spider re-
quire a very different mode of proceeding, as its line must
* " Insect Architecture," 337.
SPIDERS AND MITES. 215
be instantly converted from a fluid into a strong rope,
or it would be of no use for the purposes it is intended
to fulfil. Let a fly, for example, become entangled in
the meshes of a Spider's web; no time is to be lost ; the
struggling victim, by every effort to escape, is tearing
the meshes that entangle it, and would soon succeed in
breaking loose did not its lurking destroyer at once rush
out to complete the capture and save its net, spun with
so much labour, from ruin. With the rapidity of thought,
it darts upon its prey, and before the eye of the spectator
can comprehend the manoeuvre, the poor fly is swathed
in silken bands, until it is as incapable of moving as an
Egyptian mummy. To allow the Spider to perform such
a feat as this, its thread must evidently be instanta-
neously placed at its disposal, which would have been
impossible had it been a single cord, but being sub-
divided into numerous filaments, so attenuated as we
have seen them to be, there is no time lost in the
drying; from being fluid they are at once converted into
a solid rope, ready for immediate service." *
IS o doubt you have often admired the exquisite regu-
larity of those Spiders' webs which are called geometric;
that of our abundant Garden Spider, for instance. You
have observed the cables which stretch from wall to wall,
or from bush to bush, in various directions, to form the
scaffolding, on which the net is afterwards to be woven ;
then you have marked the straight lines, like the spokes
of a wheel, that radiate from the centre to various points
of these outwork cables, and finally the spiral thread that
circles agaiu and again round the radii, till an exquisite
net of many meshes is formed.
But possibly you are not aware that these lines are
formed of two quite distinct sorts of silk. It has been
shown that the cables and radii are perfectly unadhesive,
while the concentric or spiral circles are extremely viscid.
* " Nat. Hist, of Anim.," ii. 339.
216 EVENINGS AT THE MICROSCOPE.
Now the microscope, or a powerful lens, will reveal the
cause of this difference ; the threads of the cables and
radii are perfectly simple, while the spiral threads are
closely studded with minute globules of fluid, like drops
of dew, which, from the elasticity of the thread, are
easily separated from each other. * These are globules
of viscid gum, as is easily proved by touching one or two
with the finger, to which they will instantly adhere ; or
by throwing a little fine dust over the nets, when the
spirals will be found clogged with dirt, while the radii
and cables remain unsoiled. It is these viscid threads
alone that have the power of detaining the vagrant flies
which accidentally touch the net.
The diversity in the secreting organs already alluded
to, as well as in the spinnerets, is no doubt connected
with this difference in the character of the silk ; and it
is worthy of remark, that this diversity is greatest in
such Spiders as the Epeirce, which spin geometric nets.
Immense is the number of globules of viscidity that
stud the spiral circles of one of these nets. Mr. Blackwall,
the able and learned historian of the tribe, has estimated
that as many as 87,360 such pearly drops occurred in
a net of average dimensions, and 120,000 in a large net
of fourteen or sixteen inches diameter ; and yet a Spider
will construct such a net, if uninterrupted, in less than
three-quarters of an hour.
Scarcely less admirable are the ease and precision with
which the little architect traverses her perpendicular or
diagonal web of rope, — a skill which leaves that of the
mariner who leaps from shroud to backstay in a ship's
rigging immeasurably behind. To understand it, however,
in some measure, look at this last joint of one of the feet
* Mr. Richard Beck (" Trans. Micr. Soc," ix. 17) has ascertained that
the spiral thread is, when first spun, of uniform thickness ; but, after
some exposure, the viscid matter spontaneously accumulates at most
regular distances, and forms itself into globules, which are larger and
smaller alternately. It is a beautiful example of molecular attraction.
SPIDERS AND MITES.
21'
of our well-used Clubiona. It is a cylindrical rod, ending
in a rounded point ; every part of its surface is studded
with stiff, rather long, horny bristles, which, springing
from the side, arch inward towards the point. Now this
array of spines effectually prevents a false step, for if any
part of the leg, which is sufficiently long, only strike the
thread, the latter is certain to slip in between the bristles,
and thus to catch the leg. But more precision than this
is requisite ; especially when we observe with what de-
licacy of touch the hinder feet are often used to guide the
thread as it issues from the spinnerets ; and particularly
with what lightning-like rapidity the larger net-weavers
will, with the assistance of these feet, roll a dense web-
of silk around the body of a helpless fly, swathing it
up, like an Egyptian mummy, in many folds of cloth,
in an instant.
Look, then, at the extreme tip of the ultimate joint.
Two stout hooked claws of dark horny texture are seen
proceeding from it side by side, and a third of smaller
size, and more delicate in appearance, is placed between
them and on a lower level. The former have their under
CLAWS OF SPIDER.
or concave surface set with teeth (eighteen on each ii*
this example), very regularly cut, like those of a comb,
which are minute an the commencement of the series
near the base of the claw, and gradually increase in
length to the tip. These are doubtless sensible organs of
touch, feeling and catching the thread ; and they, more-
over, act as combs, cleansing their limbs, and probably
218 EVENINGS AT THE MICROSCOPE.
their webs, from the particles of dust and other ex-
traneous matter which are continually cleaving to them.
There are Spiders in the sea also. I can show you one
which is sufficiently common on the southern shores,
sprawling and crawling sluggishly among the filamentous
sea-weeds and branching flexible zoophytes. Here it is,
Nymphon by name.
Its most prominent characteristic is the exceeding slen-
derness of all its parts, but especially its eight legs, which
are greatly lengthened, each comprising eight joints, and
no thicker than the finest thread. On the other hand,
the body is reduced to a minimum ; the abdomen, which
in the Spiders and Harvestmen of the land is so bulky as
to constitute the chief volume of the animal, is here so
minute that you will have some difficulty in finding it
at all ; it is, in fact, that tiny atom of a point that
projects between the hindmost pair of limbs. The
thorax, indeed, is a little more developed ; but even
this has scarcely any appreciable breadth or thickness,
being little more than the extended line formed by
the successive points of origin of the limbs.
The head, however, is distinct and well furnished. It
is crowned with a short column, much as in the Harvest-
man, on the summit of which are placed four black eyes,
set in square ; these, under the magnifying power which
we are applying to them, gleam like diamonds, the light
being highly refracted through them. It is the high
refractive power of these eyes, as of those which we
have lately been examining, which makes them appear
black ; for, as I have explained, they are really trans-
parent lenses, covered with polished cornea?, and
furnished with the other essentials requisite for the
transmission of the rays of light to the optic nerve, or,
as in this case, direct to the brain.
In front, you see, the head projects into a stout oval or
cylindrical proboscis, terminating in a small mouth and
SPIDERS AND MITES. 219
stout jaws, and furnished at the sides with a pair of spine-
like palpi, and a pair of pincer-claws (modified antennae)
somewhat resembling the nippers of a Crab or Lobster.
Such is the outward form of this tiny speck, the whole
body of which scarcely equals in dimensions a quarter of
an inch of sewing cotton. And now I will beg your atten-
tion to the singular manner in which digestion is carried
on in this atom. You will discern it plainly enough
through the brown, but translucent skin. If you look
carefully at either of the long, many-jointed legs, you will
see that it is permeated by a central vessel, the walls of
which contract periodically with a pulsation closely resem-
bling that of a heart, by which granules or pellucid
corpuscles, floating in a clear fluid, are forced forward.
There is no uniformity in the direction of the pulsatory
waves ; sometimes, as in the limb we are watching, they
proceed from the body towards the extremity ; but, in
some of the others, we shall probably find, even at the
same moment, that the waves have an opposite course ;
and this contrariety may occur in two contiguous limbs on
the same side of the animal. By continuing our obser-
vation for some minutes, we shall find also that its force
is varying and uncertain ; strong and regular at one time,
weak and irregular at another, and sometimes even quite
intermitted, or, at least, quite imperceptible.
By selecting a limb in which the movements are strong,
you may trace the vessel to its termination in a blind sac
in the last joint but one of the limb ; and then follow it
up to its junction with a great vessel which runs longi-
tudinally through the trunk, of which all the vessels that
permeate the limbs are branches, and whence the circu-
lating globules all proceed. This great vessel is the
stomach; and this circulation is the provision for dis-
persing the nutritive properties of the food to all parts
of the system. There is, in these humble and simply-
organised animals, no proper blood ; or, at least, none
220 EVENINGS AT THE MICROSCOPE.
included in a system of arteries and veins ; but the pro-
ducts of digestion are carried to the most distant parts of
the body through this extraordinary development of the'
stomach or intestine (both in one), and through this series
of blind canals, by means of their own irregular con-
tractions, aided by the muscular movements of the body
and limbs.
You would scarcely forgive me if I took do opportunity
of showing you the Cheese-mite, that first object of wonder-
to every child that looks through a magnify ing-glass. And
it could not be more suitably introduced than in con-
nexion with its cousins, the Spiders and Harvestmen.
Well, fortunately, we need not search far for specimens;
for here, in the cavity of this almost defunct skeleton of a
cheese, we can find as many millions as you can reasonably
desire to select from. Here is a fat one; we will take him.
You can see with a pocket lens that it has a plump,
polished, oval body, of a pellucid white hue, and eight
short red legs ; but for more than this we must go to
the tube. Look at him now, as he lies on his back,,
helplessly sprawling and throwing his feeble legs about,
in the live-box.
His oval body is divided by a transverse furrow into
thorax and abdomen, like a Beetle's; and there is another
division between the head and thorax, wherein it differs
from the Spider's. The first two pairs of legs are separ-
ated by an interval from the last two pairs ; they are all of
a translucent pale red hue, as is also the head : each con-
sists of seven short joints, the last of which has a sort of
heart-shaped pad, something like a horse's hoof, and a
single hooked claw, which works against its sole.
The structure of the head cannot be seen satisfactorily
otherwise than by crushing the Mite in the compressorium;.
a process which, when we remember how many thousands
we crush down in our oral compressorium every time we
eat ripe cheese, needs not excite much compunction. We
SPTDERS AND MITES.
221
must put a drop of water between the plates, in order to
wash away the opaque granules which will escape from the
bodies of the animals; after which the skin, and all the
solid parts, will be left beautifully clear and distinct.
Moreover, by putting half a dozen specimens in at once,
we shall secure them pressed in various aspects, and be
pretty sure of some perfectly flat and symmetrical.
I have one under such conditions ; the parts of the
mouth nicely expanded, and the whole well displayed.
Xoav for a high power ; for, to discern this properly, we
■cannot do with less than 600 diameters.
HEAD OF CHEESE-MITE.
Viewed from beneath, we see a broad labium, nearly
square, divided at the tip into two blunt points, with a
sharp notch between them. The two lateral edges are, as
it were, buttressed by the pair of palpi, which are thick,
and consist of four joints each ; these are distinguished
by the bristles at each joint, though the whole are united
or soldered, as it were, to the sides of the lip.
The upper portion of the mouth is formed by two stout
mandibles, which are jointed to the front of the head, and
can be either widely expanded, or brought together, so
222 EVENINGS AT THE MICROSCOPE.
as to form a covering to the labium. They are pincer-
form, like the claws of a crab, the two fingers being
strongly toothed on their opposing surfaces. They thus
form effective prehensile instruments. These mandibles
can be advanced separately or together, and the whole
head can be elevated or depressed.
In the water of ponds we may frequently see, playing
among the sub-aquatic vegetation, bright-coloured Mites ;
sometimes rich velvety green, sometimes purple, but more
commonly brilliant scarlet; often curiously marked with
sinuous patterns or spots of black. They swim freely
and evenly, by means of rapid rowings with their legs,
which are thickly fringed with long hairs. I have one
here, which seems to be the Hydrachna histrionica. It
is a little, flat, circular, cushion- or cake-like creature,
scarlet, with four clouds of black on its back, and about
one-sixth of an inch in diameter. You may notice the
effective oars which the legs form, by means of their
thick fringe of hair ; and, in particular, the power
which the hind pair possess, by reason of the enor-
mously dilated hip-joint, affording space for broad and
powerful muscles.
In the structure of the mouth it differs greatly
from the Cheese-mite. The palpi here are long and
perfectly free throughout ; the fourth joint is long
and slender, and is curiously hollowed at the end to
receive the terminal joint, which forms a short claw, and
which falls down upon the former. The mandibles, too,
are not pincers, but consist each of a thick joint, cut oft
obliquely behind, like the nib of a pen, while the other
extremity is blunt and broad, and bears a strong curved
claw; the lip is oval, and cleft in the middle, and is
wedged in between the bases of the first pair of legs.
"VVHEEL-BEARERS. 223
CHAPTER XIV.
WHEEL-BEARERS.
I must now introduce to you a class of animals peculiarly
microscopic ; since, without our marvel-showing instru-
ment, they are wholly beyond the sphere of human cog-
nizance. Yet they have been, ever since its invention,
favourite objects with the microscopist ; and I am free to
confess that, among all the classes of animated beings, this
of the Rot if era* has been my own special delight. Their
numerous and varied forms, often of remarkable sym-
metry and elegance, their swiftly-revolving wheels, their
vigorous and sprightly motions, their curious habits and
instincts, their complete organization, and the ease and
correctness with which this is discerned through their
tissues, which have the transparent brilliance of the
purest crystal, — all combine to impart a charm to the
Wheel-bearers, which makes the observer hail their
appearance in his drops of water with pleasure, and
linger over them with unwearied delight.
The peculiarity which specially characterises them is
the presence of certain organs called cilia : and their
arrangement in such a manner, that their motion gives
to the observer the impression, that two toothed wheels
are placed on the front of the animal, which are in rapid
revolution on their axes. This was believed to be the
real fact by the earlier microscopists, though they were
utterly unable to conceive how such a movement could
consist with parts maintaining an organic connexion
* From the Latin rota, a wheel, and/ero, I bear.
224: EVENINGS AT THE MICROSCOPE.
between themselves. It is, however, an optical illusion,
depending on the nature of ciliary movement, which
therefore I must lirst endeavour to explain to you.
Cilia are organs which play a very important part as
instruments of locomotion, as well as of other functions,
in all the lower forms of animals, and in the early stages
of some of the higher forms. They are also found cha-
racterising the lowest form of vegetable life, giving to them
the means of spontaneous locomotion, which renders them
liable to be mistaken for animals. They consist of pro-
longations of the fleshy tissue into long and very delicate
hairs, which are endowed with a special faculty of motion.
This consists of a bending down in a given direction to a
certain extent of flexure, followed by a rapid resuming of
the perpendicular ; which is, however, immediately suc-
ceeded by like bendings and straighten ings in alternate
gradation. The simplest condition of this movement is
that in which a single cilium only exists, by whose suc-
cessive lash-like beats upon the surrounding water the
animal is rowed along like a boat through the sea. But,
far more commonly, cilia are arranged* in rows, or in many
series of rows; in which case the bending and straightening
of the individual cilia do not occur otherwise than in strict
•and orderly relation to each other. For instance, one
cilium in a given row begins to bend, the one next to it
then begins, then the third, then the fourth, and so on, all
precisely in the same direction, all in precisely the same
time, all with precisely the same force, and all to precisely
the same extent. It follows, that before the first has com-
pleted its beat and resumed the erect position, three or
four others are in various degrees of flexion, regularly
graduated; and that if the eye could look laterally at such
a row of cilia suddenly arrested and fixed as they were,
we should see their tips tracing a wavy line instead of a
straight one. Moreover, since the bending of any cilium
brings its tip nearer to its successor than it was before,
WHEEL-BEARERS. 225
and this approximation increases the farther the flexure
proceeds, it follows that at the bottom of each wave the
tips of the cilia overlap their successors, while the spaces
perpendicularly above their bases are left more open by
the removal of their points.
Hence, in microscopical observation of ciliated animals,
though the individual cilia are too minute to be discerned
while motionless, Ave can readily discern the increased
density (and therefore opacity) of the bottom of a wave,
contrasted with the increased openness (and therefore
clearness) of the summit. So that the optical effect is
that of an alternate succession of dark and light spots
blending into each other.
But as no cilium in the series is for two successive
moments in the same degree of flexure, and as both it
and all its predecessors and successors are ever urging
on their perfectly timed and regulated course, the waves
are never fixed, but always gliding on with a swift but
beautifully even rapidity. And as it is with the waves,
so it is with their optical effect upon the eye ; the black
and white spots, or rather the black spots with blank
intervals, appear to be constantly chasing each other in
ceaseless race.
You are then prepared to take a peep at this beautiful
Brachionus pala. A cup of elegant form, swelling at the
sides and narrowing a little at the mouth, has one side
of its rim furnished with four spines, the middle pair of
which are very slender, sharp, and needle-like; the other
side of the rim is undulated, but not toothed. The
bottom of the cup terminates in two broad, blunted
points, when seen directly in front ; but a lateral view
considerably modifies the whole form. Then you see that
the back of the cup is much more swollen, the belly-edge
being nearly straight, and that this latter descends much
lower than the dorsal line, the bottom being as it were
cut away obliquely and slightly hollowed. Between the
Q
226 EVENINGS AT THE MICROSCOPE.
two bottom points, there is a round opening, for an
object which we shall see presently. Such is the shell,
or lorica, as it is technically called, which is of a rather
stiff, elastic consistence, of a horny (chitinous) texture,
and of the most glassy transparency, permitting us to
trace every vessel, every organ, and every function of the
animal within the shell, with perfect distinctness. The
little creature is of unwonted dimensions in its class, for
it is one thirty-sixth of an inch in length. Hence, to the
unassisted eye, it is just visible as a white speck moving
in the water, while a pocket lens reveals its beautiful form.
Within this translucent shell you see a confused mass
of moving viscera, a multitude of irregular sacs and
bands, lying over each other, whose crowding, changing,
and vanishing lines distract the attention, and prevent
you from making out anything definitely. But a waved
outline of limpid flesh is protruding from the rim of the
shell ; and now, having reached beyond the level of the
spine-points, it rapidly unfolds into three broad, flattish
lobes ; and in an instant each of the two lateral ones is
crowned by a wheel of dark points in rapid horizontal
revolution. Is not this a charming sicrht 1 Round and
round go the wheels, forming two perfect crowns, which
rotate with uninterrupted and unceasing course, smooth
and regular, which we can compare with nothing else
than the crown-wheel of a watch, if allowed to run down.
Now these are examples of ciliary action. Though at
first it is almost impossible to persuade oneself that there
is not an actual rotation of parts, yet this is only an illu-
sion, as I have already explained. The waves alone move,
the cilia themselves retaining their position unchanged,
except that they alternately bend and erect themselves.
It may assist your idea of this motion to advert to a field
of corn over which a smart breeze is blowing. You see
that waves chase each other across the field ; but your
reason, indeed your observation, tells you, that this appear-
WIIE EL-BEARERS. 227
ance is produced entirely by the alternate bending and
rising of the ears of corn, which are of course stationary.
The beauty and wonderfulness of these ciliary wheels
are so striking, especially when one sees them for the
first time, that for awhile we see nothing else; we cannot
take our eye off from them. But when you have a little
satisfied your sense of seeing, you may examine other
points of interest in this charming little animal.
The cilia are remarkably stout and long in this genus,
but on the middle lobe of the front there are other pro-
cesses of the same character; but still stouter. These
too are not properly vibratile, at least they do not make
circular wheels : ordinarily, they project like stiff erect
bristles, or converge towards each other.
Between the two middle spines the shell is cut into a
deep notch, out of which protrudes, when the wheels are
expanded, a curious little organ, consisting of fleshy tubes,
the one sheathed in telescopic fashion within the other,
and bearing at its tip a pencil of bristles, which can in
turn be sheathed. This organ doubtless represents the
united antenna? of insects.
But, you ask, what is that much more conspicuous
organ that is alternately thrust out and drawn back at the
bottom of the shell, and that is so nimbly whisked about
in all directions, looking, with its numberless transverse
wrinkles, and its little fingers at the tip, so like an ele-
phant's trunk in miniature % This is the creature's foot ;
the only one he has ; and, as I said, the little tubular tele-
scope represents the two antenna? fused into one, so we
must consider that this flexible member represents all
the six pairs of an insect's legs united, or perhaps, more
scientifically, one of the pairs, the rest being obsolete or
undeveloped. It must not be considered as a tail ; not
only from its function, which is decidedly that of loco-
motion, but also from its position on the ventral side of
the intestinal orifice. It is a curious organ, capable of
Q 2
228 EVENINGS AT THE MICROSCOPE.
great elongation, or, at the will of the animal, of entire
retractation within the abdomen ; and this in an instant:
while, as you observed, it is flung about, and dashed from
side to side, and bent hither and thither with a sort of
insane energy. The means by which these movements
are performed, you may easily discern in several pairs
of muscular bands which run throughout its whole
length, their upper insertions being placed high up on
the interior of the shell, where, during contraction, you
may see them swollen into thick bulbs.
The foot terminates in two short conical fingers or
toes, which can be drawn in or extended, widely separ-
ated or brought into contact, at jDleasure. By means of
these the animal has the power of mooring itself, even
to the smooth surface of glass ; and that so firmly that
from them it can stretch itself in all directions by turns,
now and then shaking itself to and fro with sudden vio-
lence, as if irritated, yet without letting go its foot-hold.
While thus anchored, the action of the ciliarv wheels
produces considerable whirlpools in the surrounding water,
as you will see very distinctly when we have recourse to
a curious but simple expedient, first invented by Gleichen,
and since much used by Ehrenberg, of mixing some
colouring matter with the water in which the animal is.
I take a little carmine with a wetted hair-pencil, as if I
were going to colour a drawing, and allow a small portion
of the pigment to diffuse itself in the water which is in
the live-box ; then, putting on the cover, I quickly
replace the whole on the stage, and re-find my little
Brachion : and now I again submit it to your observation.
The whole field is now filled with scattered granules of
irregular form and size, of a dark red hue. These are the
particles of carmine floating in the water ; particles of
alumina, that is to say, stained with cochineal. They are
in motion, and their movement is more energetic the
nearer they are to the little animal, which is rotating
"WHEEL-BEARERS. 229
vigorously in the midst of them. They describe two great
circles, concentrical with the twowheelsof the Brachionus,
and it is easy to see that their rotations are the cause of
the movement. The motion of the cilia communicates
itself to the surrounding water, and produces circular
currents, into which every floating atom within a certain
distance is drawn, and in which it then continues to
whirl round with a rapidity which increases as it ap-
proaches the centre of rotation.
But the Bracldonus suddenly lets go its foot-hold, and a
surprising change takes place. Ko more currents are made
in the water, but the animal itself glides swiftly away head
foremost with an even course, revolving on its axis as it
goes. What is the immediate cause of its movement 1
The ciliary action which before produced vertical currents.
In order to explain this, let me suggest to yon a homely
comparison. Suppose you see a boat on a still lake, and
in it a man pulling a pair of oars. He pulls vigorously,
but the boat does not move an inch, and you perceive that
she is fast moored ; a rope holds her to a post on the
bank. But does the man's rowing produce no effect 1 O
yes; the successive strokes of the oars upon the water
have communicated motion to the fluid, and a strong
current is made on each side of the boat, in a direction
opposite to that in which he strives to row her forward,
the force of which is felt to a distance proportionate to
the vigour and continuance of his pulling. The reason
of this is that the boat is fixed, and all the force of the
impact is spent on the water.
But now another man approaches the post, and unties
the rope. Instantly the boat glides ahead, and continues
to do so, urged by the repeated strokes of the oars, whose
effect on the water in making currents is now slight and
imperceptible. The reason of this is that the water is
now a fixed body (or nearly such), and the force of the
impact is mainly spent on the movable boat.
230 EVENINGS AT THE MICROSCOPE.
The Brachionus is the boat, its cilia are the oars, and
its foot is the rope. As long as this last maintains its
hold, the whole force of the ciliary stroke is spent on the
water, and currents are the result ; but as soon as this
hold is broken, the force acts on the animal (= boat),
which is thus rowed rapidly forwards. ■■
The use of the cilia in this latter case is obvious. They
enable the little animal -to rove about at its wayward
will ; and doubtless motion is as pleasant and necessary
to it as to the fish in the sea, or to the bird in the air.
But what is the object of their vigorous rotation, when
the animal chooses to maintain a firm hold with its foot %
What is the use of rowing a boat, if you do not choose
to let go the painter 1
To solve this enigma, let us search up our little
Brachion once more; he will not roam long before he
settles soberly again. Yes, here I have him moored. Now,
mark carefully the vortices, or whirlpools, which are so
vigorously circling round the animal's front, and you will
perceive that the movement is not a strictly circular one,
but that each whirlpool has an outlet close to the cilia; for
the accumulated and condensed particles of pigment, after
many rotations pass off in an united stream between the
two crowns, and go away horizontally in a line from the
ventral side of the front. That is to say, each vortex
pours off its accumulation at a point on the inner side of
the ciliary circle, and the two streams, uniting, pass off
from the lip of the shell, to be drawn in again, however,
by-and-by, when the centrifugal force is exhausted.
Now this stream passes immediately over the mouth,
which is an opening in the flesh of the front, forming a
deep cleft on the ventral side, the lips of which, as also
the whole interior of the tube, of which it is the orifice,
are richly covered with cilia. A certain portion of the
atoms are thus arrested by these cilia, and are hurled by
their vibrations clown this gulf. Yet not all, nor nearly
WHEEL-BEARERS. 231
all; for the lips appear to possess the sense of taste, or of
some modification of touch, which enables them to refuse
or to receive the atoms presented to them, so that only
such particles pass down the throat as are selected for
food. Some of the atoms of pigment are admitted, and
one of the most pleasing sights connected with these
animals, is to watch the swallowing of coloured food, its
reception into the singular sunken mouth, where the
great powerful jaws act upon it: thence its dismissal
through the gullet, where certain glands pour upon it
their secretions, into the stomach, where other glands,
answering to a liver, change it ; and thence into the
intestine and rectum, until its indigestible portion is
discharged through the cloacal orifice.
The object of the mingling of colour Avith the water in
which these and similar animals are held for observation,
was the tracing of the phenomena of digestion. And,
indeed, it renders the whole process beautifully distinct;
for, from the transparency of the tissues, the presence
of the coloured pellet is everywhere recognizable, since
it retains its form and hue under all its changes, clearly
revealing to us the shape, dimensions, and directions of
the various canals through which it passes; here and
there diffusing throughout the viscus in which it is held
a beautiful roseate hue, more or less deep, without, how-
ever, causing- it to lose its own definite outline.
Let me now direct your attention to the organs devoted
to the seizing and mastication of the food. And the
more, because the form of these organs in the Rotifera is
quite peculiar, quite unlike what is found in any other
class of animals; though the parts are essentially the
same as those which we have already seen entering into
the mouth in insects.
Removing the carmine-stained water, I put into the
live-box a drop from a vase very rich in organisms of
many kinds. Among these you see very numerous the
232
EVENINGS AT THE MICROSCOPE.
mulberry-like clusters of that beautiful green creature,,
Syncrypta volvox, which is now pretty generallyconsidered
a plant ; though from its spontaneous motion, swimming
evenly along, revolving on its axis as it goes, you would
be inclined to asjree with earlier observers in thinking it
an animal. These appear to be favourite morsels with the
Brachion : one has already been devoured, and is quite
visible in the alimentary canal, its brilliant green hue
shining out through the translucent viscera and tissues.
^ Others are approaching,
a\u\ ^N- u "-;, and two or three are iust
0> now drawn into the vor-
tex of the ciliary current.
It is amusinff to see the
manoeuvres which the J3ra-
chionus makes to take his
prey. I say manoeuvres ',.
for there reallv seem to
•J
be perception and intelli-
gence. The mode inwhich
it directs its ciliated flaps
towards the spot where a
Syncrypta is whirling, or
suddenly stretches forward
to the extent of the long
foot, as if it would seize
the prey by force, seems
to indicate a cognizance of
its proximity; as do also,
still more, the manner in
which it depresses the lip-
like lobes of the rotatory organ on one side, when the
prey is in the vortex on that side, and the eager haste
with which it shrinks down into its shell the instant the
little mulberry drops at length into the throat.
But now comes the tug of war; the black, millstone-
BKAC'HIOXUS.
WHEEL-BEARERS. 233
like jaws open wide, and stretch forward to grasp the little
victim (which is still distinctly visible through the trans-
parent tissues) : they touch the globular envelope, but
cannot quite grasp it. The Brachion redoubles its efforts ;
the jaws gape vigorously, but can only scrape the sides of
the little globe, which at every touch slips away, the ex-
panse of the jaws being not quite sufficient to embrace it.
At last the little animal becomes indignant ; the jaws
no more endeavour to grasp, but with a very distinct and
sudden upward jerk throw out the prey, which until now
has been retained and pressed downward by the contrac-
tion of the sides of the sensitive throat. Strange to see,
the little Syncrypta, after all its imprisonment and rough
handling, is no sooner free than it whirls merrily away,,
revolving as it pursues its even ciliary course, just as if
no interruption of its freedom had occurred.
Meanwhile, however, better success attends the Bra-
chion's hunting ; for a smaller globe has sunk into the
throat, and passed with a gulp into the mouth between
the gapingjaws; which instantly close upon it, and, working
vigorously, bruise it down with a hammer-like action upon
a sort of central table. After this process has gone on
for a few minutes, the green mass, less perfectly denned
than before, slips through a narrow postern-gate, along
a short slender alley, into the digesting stomach.
But what sort of a mouth is this 1 It is inclosed
within the tissues of the body, not very far from its
centre, so that no part of it comes into contact with the
external water, or even approaches any portion of the
superficies of the body. It has been usual to call the
great hemispheric bulk in which the symmetrical
hammers work so vigorously, a gizzard ; but it is a
true mouth, and the hammers are true jaws.
This form of mouth is termed a mastax ; it consists of a
dense but transparent muscular mass, forming three lobes
at its lower part, deeply cleft at the front of its ventral
234 EVENINGS AT THE MICROSCOPE.
side, where the passage, which I have called the throat,
but which is more correctly designated the buccal funnel,
enters. Within this muscular bulb are placed two bent
organs like hammers, called mallei, and a third central
table, called the incus. The mallei approach each other
dorsally, while the incus is placed towards the ventral
side, its stem pointing obliquely away from the centre.
Each malleus consists of two portions, united by a free
but powerful hinge-joint. The lower joint (manubrium)
is shaped somewhat like a shoulder-blade ; and the upper
joint (uncus)* is set-on at nearly a right angle to it, but
is capable of considerable change of direction by means
of its hinge. It consists of five or six finger-like teeth,
connected by a thin web of membrane.
The incus also consists of several distinct pieces. The
principal are two stout rami, resting on what appears,
when you look at the back or belly of the animal, to be a
slender foot-stalk (fulcrum). But when you get a lateral
view, the foot-stalk is seen to be only the edge of a thin
plate, to the upper edge of which are jointed the rami, in
such a manner that they can open and close, like the
blades of a pair of shears. Each ramus is a thick, three-
sided piece, with the upper side hollow, and the inner
flat, and in contact with that of its fellow, in a state of
repose. The uncus of each malleus falls into the concavity
of its corresponding ramus, and is fastened to it by a stout
triangular muscle, which allows some freedom of motion.
Many muscles are inserted into diflerent parts of these
organs, and into the walls of the inastax, which impart
various and complex motions to all the parts. Thus, as
we have seen, they are adapted to the various functions
of mouth-organs, those of grasping, holding, bruising,
and chewing food.
The mallei correspond with the mandibles of Insects ;
* The uncus of the malleus must not be confounded with the incus.
WHEEL-BEARERS.
235
SIOUTH OF BKACHIONUS.
and the rami of the incus with the maxilla? ; while the
walls of the mastax with the two edges of its orifice
correspond with the mouth, with
its labrum and labium.
It is true we are somewhat
startled to find a mouth placed
far down within the cavity of the
breast ; but there are other
forms in this class, some of
which I may be able to show
you, where the mastax has es-
sentially the same structure, in
which it is placed at the front
margin of the body, from which
the jaws can be freely protruded.
The difficulty will seem less if you weigh the following
considerations : —
The integument in the Rotifera is very flexible, and,
especially in the frontal regions, is extremely invertible.
In those genera in which the mouth-apparatus can be
brought into contact with the external water, it is ordi-
narily, to a greater or less degree, retracted within the
body, by the inversion of the surrounding parts of the
exterior ; while, in those genera in which it is per-
manently inclosed, analogy requires us to consider the
condition as induced by a similar inversion, but of per-
manent duration. If we imagine the head of a soft-
bodied Insect-larva retracted to a great degree (as is done
partially by many Dipterous larva?), the skin of the
thoracic segments would meet together in front, around
a purse-like opening, which would be the orifice of such
a buccal funnel as exists in most Rotifera. In the latter,
it is the normal, or proper condition ; in the former, it
is merely accidental and temporary.
We need not devote any more minute consideration to
the digestive apparatus in our little Brachion, but there
236 EVENINGS AT THE MICROSCOPE.
are some other points in its structure which are worth
noticing. In the central line of the body, just above the
mouth, as you see the animal in a dorsal view, there is a
square speck of a rich crimson hue, the edges of which,
when we view it under reflected light, glitter and sparkle
like a precious stone. But when we obtain a perfectly
lateral view, we perceive that the situation of this gem-
like speck is considerably nearer the dorsal side of the
shell than the mouth, and that it forms a wart-shaped
prominence on a large turbid mass which occupies the
whole front portion of the animal. By comparison of
this organ with the corresponding parts in other genera,
there is every reason to infer that this turbid mass is an
enormous brain, the nervous matter being in a very
diffuse condition ; and that the ruby seated on it is an
eye, consisting of a crystalline lens, and a layer of
crimson pigment beneath it.
The oval bodies that you see attached to the hinder
part of the shell are eggs. Most of the females that we
meet with carry one or more, sometimes to the number of
six or seven. The specimen we are examining had two at
first, one on each side the foot-orifice ; but just now a*
third was excluded, — an operation which occupied but an
instant, — and this took its place besides the former two,
so that we now see three. These eggs are generally car-
ried by the parent until the young are hatched. The
oldest of these three is nearly ready for hatching ; and
if you watch awhile you will see the birth of the young.
At the first exclusion, the egg, which was seen sometime
before in the ovary, as a semi-opaque mass, of well-defined
but irregular shape, immediately assumes a form perfectly
elliptical, and its coat hardens into a brittle shell. This
is so transparent that the whole process of maturation can
be watched within the shell. The yelk is at first a turbid
mass, in which are many minute oil-globules. Soon it
divides into two masses, then into four, then into eight,
WHEEL- BEARERS. 237
sixteen, and so on, by the successive cleavage of each
division, as fast as it is made, till these divisions are very
numerous. Then we begin to see spontaneous movements ;
the outline of the young separates in parts from the wall
of its prison ; folds are seen here and there, and litful
contractions and turnings take place. Soon an undefined
spot of red appears, which gradually acquires depth of tint
and a definite form, and wre recognise the eye. Slight
waves are seen crossing one end of the egg ; these become
more and more vigorous and rapid, and at length we see
that here is the situation of the frontal cilia. The mastax
appears, and the jaws, and soon the latter begin to work ;
though it must be only by wray of practice, for it is hard
to imagine what they can yet find to masticate.
All these phenomena have successively appeared in the
egg we are now watching ; and at this moment you see
the crystalline little prisoner, writhing and turning im-
patiently within its prison, striving to burst forth into
liberty.
Now a crack, like a line of light, shoots round one end
of the egg, and in an instant the anterior third of the shell
is forced off, and the wdieels of the infant Brachion are
seen rotating as perfectly as if the little creature had had
a year's practice. Away it glides, the very image of its
mother, and swims to some distance before it casts anchor,
beginning an independent life. At the moment of the
escape of the young, the pushed-off lid of the egg resumes
its place, and the egg appears nearly whole again, but
empty and perfectly transparent, with no evidence of its
fracture except a slight interruption of its outline, and a
very faint line running around.
This is a female young : the male is totally unlike the
female, and is very much smaller. \Ve can always tell
whether an egg is going to produce male or female
young, by the great difference in its size, the female
being more than twice the bulk of the male egg. All
238 EVENINGS AT THE MICROSCOPE.
of one brood are of the same sex ; we never see a
Brachionus with male and female eggs at the same time.
"What is very strange, is, that the male has no shell, no
spines, no mouth, no jaws, no stomach, no intestines ;
no ciliary wheels ; its cilia, which are very long and
powerful, being arranged in one circle round the whole
front. Its movements are exceedingly fleet.
Perhaps you are tired of Brachionus, and are ready to
cry out, " Ohe ! jam satis ! " * Well, then, I will turn
him off, and show you another elegant little creature, the
Whiptail (Mastigocerca carinata). I have here in a bottle
some stalks of the Water-Horsetail (Chara vulgaris)
which I obtained from a pond a few weeks ago. These I
examine in this way. Taking hold of the Chara with a
pair of pliers, I pull it partially out of the water, and
allowing it to rest on the neck of the bottle, I cut off with
a pair of scissors, or with a penknife on my nail, about
one-fourth of an inch of the tips of three or four leaves,
which adhere together by their wetness. These tips I
place in the live-box, with a drop of water, and having
separated them with a needle, I put on the cover, and
examine them with a triple pocket lens ; holding up the
box perpendicularly, not opposite the light, but obliquely,
so that the field is dark ; but the light reflected and re-
fracted by the animalcules shows them out beautifully
white and distinct, even the minute ones. The forms
and some characters of the middling and larger can be
quite discerned thus; for example, the slender tail of the
one I am now going to show you, I can thus see. The
position of any particular individual to be examined
being thus marked, it is readily put under the object-
glass of the microscope. I have found these leaves very
productive of the more stationary animalcules, the
Rotifera especially.
It was in this way I this morning found the pretty and
* " 0 dear ! quite enough of tli;s ! "
WHEEL-BEAKERS. 239
delicate little "Whiptail, which I am going to make the
subject of our evening's study. It is inclosed in a glassy-
shell (lorica) of a long oval form, from which rises on the
front half of the back a thin ridge, which in the middle
has a height nearly equal to half the diameter of the body,
but tapers off at each end. Its base is corrugated with
wrinkles. This is not set on symmetrically, but leans over
considerably to the right side. Its basal portion is hollow,
and is continuous with the general cavity of the shell, for
we sometimes see portions of the viscera in its interior.
WHIPTAIL.
The head of the animal is rounded, and divided into
several blunt eminences or lobes, which are set with cilia;
these rotate constantly, but irregularly and feebly, and do
not make manifest wheels, as Brachionus does. A small
antenna projects from the back of the head, capable of
being erected or inclined. A long brain descends along
the base of the ridge, carrying a bright and rather large
crimson eye set like a wart on its interior angle.
Instead of the flexible and contractile foot of Brachi-
onus, the Whiptail has a single horny spine of great
slenderness, and exceeding in length" the whole body.
This spine probably represents not the foot, but one of
the toes at the end of the foot. For it is attached to a
very short foot, in the midst of two or three bract-like
spines, one of which, longer than the rest, and distinctly
movable, probably represents the other toe undeveloped.
The long spine is set-on by a proper joint, a globose bulb
being inserted into a socket, which allows it free motion
in all directions except backward. The socket itself is
contained in a second joint, the basal part of which is
240 EVENINGS AT THE MICROSCOPE.
inserted at some distance within the aperture of the
lorica. This articulation is formed by an infolding of
the skin, but is permanent in its position.
The most remarkable circumstance connected with this
elegant little animal is the unusual form of the dental
apparatus, which differs so immensely from that of
Brachionus, that we should never recognise it as consist-
ing of the same organs, if we had not numerous inter-
mediate links, which by insensible gradations connect
the two remote forms.
The mastax is a somewhat slender sac, much produced
in length, and with the component lobes greatly and
irregularly developed. The incus has a fulcrum of great
length and slenderness, a straight rod with a dilated
foot. The rami are small, and pincer-shaped, but with
the angles greatly produced. The mallei have long,
slender, incurved manubria, and simple unci.
But the remarkable circumstance is the unsymmetrical
character of the apparatus. The left side is much more
developed than the right. The left angle of the incus
descends to a greater distance than the right ; and its
extremity is spread out into a surface with several irre-
gular points, to which muscular threads are attached.
The ramus also of the same side is larger than its fellow;
so with the mallei. The manubrium of the right is com-
paratively short, very slender, and of uniform thickness;
with a long, slender, rod-like uncus, doubly bent in the
middle. The left is much longer, irregularly swollen,
clubbed at the articulation, and bearing a thick, curved,
knotted uncus, which terminates at a point not precisely
opposite the tip of its fellow. These circumstances,
combined with the unsymmetrical character of the dorsal
ridge, of the foot-spine, and of some other organs, render
this genus a highly curious one to the naturalist.
The little Whiptail is as lively in its motions as it is
elegant in its form. When swimming, it glides with con-
WHEEL-BEARERS. 241
siderable swiftness through the water, turning frequently
on its course, and often partially revolving on its long axis.
When inclosed, as is often the case, by two fragments of
the filamentous Chara, it travels along the sides of its
inclosure, nibbling, as it goes, the Hocculent and sedi-
mentary deposits on the surfaces of the leaves. The long
spine-foot is commonly carried inertly after it ; when the
animal suddenly turns, of course the tail is bent at the
basal joint, but it is not habitually whisked about, as is
the tail of firachionus, nor is it so much used as a support
or turning }X)int. The animal has the power of so using
it, however, and of adhering with considerable force to
the glass of the box, or the side of a phial by its point.
We have hitherto looked at our Botifera by trans-
mitted light ; and their crystalline transparency renders
them beautiful objects when thus exhibited. But we
will now look at the Whiptail by the direct light of the
sun upon it, condensed, but not to a burning point, by
the bull's-eye lens.
It now possesses a peculiar beauty of another character.
The body generally is colourless as a vase of glass, but
reflects the rays brightly from its polished surface. An
advancing egg in the ovary is opaque white, as is the
front part of the mastax ; the stomach and the intestine
rilled with vegetable matter are of a yellow green ; the
rotating head appears of a pale blue, and the eye shines
out as a speck of opaque vermilion.
With the dipping-tube I will now take up a drop of
water from the bottom of the Chara-j&r, allowing a little
of the loose sediment to flow in also. This is a random
cast ; we know not what we may get, though we are
pretty sure to catch something. Xow then for the ex-
amination. Ha ! here is the curious Skeleton Wheel-
bearer, Dinocharis podUum, ; — nay, several of them.
This genus is remarkable for possessing true joints in
the foot ; not merely telescopic inversions of the skin, but
R
242 EVENINGS AT THE MICROSCOPE.
permanent joints with swollen condyles, or rounded heads,
resembling those of the antennas of a beetle. Hence the
Skeleton has great freedom and precision of motion ;
using the tips of the long toes as a fixed point, it throws
its body hither and thither to a great distance, with re-
markable agility. These joints admit of forward and
lateral flexure, but you never see the body brought back-
ward beyond a perpendicular position, the swelling of
the terminal portion of each articulation precluding
further motion in that direction; just as the joints of
our knees and elbows permit bending in one direction,
but not in the other.
This is another indication that these divisions are true
joints ; and I direct your attention to the point, because
the fact helps to indicate that this class of animals has
its proper affinities with the Articulata, which has
been denied by most naturalists.
The form is curious. Elevated at the summit of a long
foot, consisting of three joints, which surmount two un-
usually lengthened and slender toes, is a vase-shaped
lorica, which is three-sided. Its surface is covered all
over with minute points, very closely set, so that it re-
sembles shagreen ; besides which it forms numerous sharp
ridges, which run across transversely. The two sides run
off into thin lateral wings, which come to a sharp edge ;
the back angle also forms a ridge, but less sharp and thin.
In front, the shell, or lorica, is as it were cut off abruptly,
like the rim of a goblet ; but out of this rises a second
column, connected with the rim by an elastic membrane,
which allows some freedom of motion. This column is
widely divided in front and behind, and rises to a point
on each side. When the rotatory front is withdrawn,
these points approach and meet, closing the orifice ; but
when the head is protruded they are widely separated.
Internally, we see the usual viscera contained in so
narrow a cavity that we are ready to suppose the walls of
WHEEL-BEARERS.
243
the lorica unusually thick ; this is, however, an optical
illusion, dependent on its dilatation into those angular
wings already noticed. The cavity penetrates into them ;
for in one of these specimens I see those curious twisted
threads that are believed to be connected with respira-
tion, within the lateral wings. The stomachs are
generally full of green and brown food, but they will
not imbibe carmine.
SKELETON "WHEEL-EEAREB.
Let us look, however, a moment longer at the singular
foot. Between the first and second joints there are two
projecting spines ; these differ much in different indivi-
duals as to their length, slenderness, and direction ; some-
r 2
244 EVENINGS AT THE MICROSCOPE.
times being quite short, at others as long as the toes ;•
generally, they arch downwards, but occasionally they
stand out straight or even curve upwards. In some
specimens the spines appear to be processes of the first
joint, but in others we can see distinctly that they belong
to a little intermediate piece between the first and second
apparent joints. Between the two toes, on the hinder
aspect, projects from the last joint a small spine, which is
perhaps the rudiment of a third toe, since we find that
number in some genera of this class. The whole foot,
including the toes, is rough with the shagreen-like points
that cover the lorica.
You have already noticed the rapidity and fitful irre-
gularity which the long and many-jointed foot confers
upon the movements of this curious little form. From
the toe-tips, as a point of adhesion, it throws its body to
and fro, or from side to side, in a peculiar manner. The
toes are sometimes sprawled out, like the legs of an ex-
panded pair of compasses ; and sometimes the joints of the
foot are suddenly bent in zig-za"g fashion, and then as
abruptly straightened. The animal swims gracefully, but
only with moderate swiftness, the rotatory crown of cilia
beinc small, though forming the usual vortices when the
animal is moored : while thus swimming, the toes are
gracefully stretched behind, nearly in contact with each
other. It is lively in its motions, but these seem per-
formed without any ostensible object : we do not often
see it attempt to eat, or nibble at any substance.
I think we never find the Skeleton except among the
sediment at the bottom of the water in which it is kept ;.
among which also we frequently seethe remains of defunct
specimens — the skeleton of the Skeleton ; this itself makes
a pretty object : the lorica, with its point and ridges, the
thoracic column, the foot with its joints and spines, and
the toes, all being perfectly preserved, and rendered even
more clear than during life, because of the removal of all
WHEEL-BEARERS. 245
the soft internal parts by decay, and by the efforts of
those little scavengers, the smaller species of infusorial
animalcules. These quickly find their way into the
interior of any dead animal with a shelly case, as a
Wheel-bearer, a Water-flea, or an Insect, and soon
devour every particle of soft flesh, cleaning out the case
in the most tidy manner.
Here is a tiny subject which will test your powers of
observation, and possibly your patience, in satisfactorily
defining its structure, partly on account of its swift motion
and irregular leaps, and partly on account of its extreme
transparency. It is a crystalline cup, somewhat like the
body of a wine-glass, without any foot, but bearing many
flat, sword-shaped processes, which, proceeding from the
breast, commonly lie flat on each side, down the body,
the points projecting below. These are evidently stiff and
highly elastic, and their use is manifest to any one who
sees the creature in active motion. It swims with a rapid
gliding progress, head foremost ; but, at almost every mo-
ment, it makes a sudden forcible jerk or leap, backwards or
to one side, and that so quickly that the eye often cannot
follow it in the transition. The organs by which these
jumps are effected are the long breast-spines, which are
suddenly thrown out in various directions ; and they may
frequently be seen extended the instant after a leap.
When we consider that the creature is jerked often four or
five times its own length, through so dense a fluid, we
shall perceive how strong the muscular action must be
which moves the lever-like spines. The creature is
thrown irregularly, often with the side foremost, or the
back ; or made to perform a somersault in the act. It is
probably a sensitiveness to danger or annoyance that
prompts these violent leaps ; at least, it frequently per-
forms them after a momentary examination of any float-
ing matter with which its course brings it into contact.
The rotatory organs, the source of the common gliding
246 EVENINGS AT THE MICROSCOPE.
motion, are not very large or conspicuous ; the cilia
appear to be set all along the brow. The eye is very
visible ; it is placed near the front, and seems to be of a
deep bluish-black hue.
I have not, however, as yet introduced the nimble
little stranger by name. "We may call it familiarly the
Sword-bearer, but Professor Ehrenberg has named it
Polyarthra platyptera.
This eminent authority on all that concerns these
minute forms has placed the species among those which
are destitute of a horny lorica or shell. But he is cer-
tainly in error here ; for, as you may see, there is mani-
festly a stiff lorica, which covers the back and sides, but
which gapes widely in the middle of the under side,
throughout its length. From the lateral points, how-
ever, a membrane may be seen for a short distance, which
doubtless protects the viscera from actual exposure.
The sword-like fins appear to be twelve in number, ar-
ranged in groups, or bundles, of three each; one bundle
being set on each side of the dorsal, and one on each side
of the ventral aspect, at about one-fifth of the entire
length from the frontal points. These are all that we can
ordinarily count ; but I have seen more ; one day, while
examining a specimen that presented a vertical aspect to
me — end-on, to speak familiarly — the fins being all ex-
panded, I saw with perfect distinctness a seventh pair,
proceeding from the middle of the breast. They are flat,
thin, narrow blades, of exceeding delicacy ; all distinctly
serrated on both edges, the teeth pointing from the base
outward : each is strengthened by a central rib. They
are jointed independently, on rounded shelly knobs, and
are doubtless moved by strong muscles. Under pressure,
the knobs and the fins are brought out with beautiful
distinctness. Here again we have true jointed limbs.
On the front you may discern a pair of tiny antennae,
each bearing a pencil of very fine bristles. And just
WHEEL-BEARERS.
247
below the level of their base, in the centre of the dorsal
region, you see the large eye, of a deep red hue, so deep
that it frequently looks as if it were actually and intensely
black. Just below the eye, apparently, but considerably
more towards the ventral aspect, there is a huge niastax,
occupying almost half the length of the whole body. The
jaws are very simple in their construction, and therefore
very instructive, for they contain the same elements as
in Brachionus; but from their excessive tenuity, and for
other reasons connected with the form of the animal,
they are calculated to tax to the utmost your perse-
verance and skill in manipulation to resolve them. They
were an enigma to me for years.
The great mastax is pear-shaped, pointing obliquely
towards the middle of the belly. This form is owing to
the great length of the fulcrum, and the wide curvature
SWOBD-BEAEEE.
of the mallei. The rami are very broad, somewhat square
at their base, flat, but much arched longitudinally. They
open and shut vigorously, with a snapping action, but are
248 EVENINGS AT THE MICROSCOPE.
not protruded from the front ; their Avhole interior edges
come into contact. The mallei are simple, slender, bent
rods, apparently without distinct articulation. During life
they are thick and irregular in outline, owing to their
being invested with dense muscles; as is the whole upper
portion of the mastax. These muscles conceal or disguise
the form and action of the parts during life ; but the intro-
duction of a drop of solution of potash into the water in-
stantly dissolves away the fleshy parts, leaving the solid
organs, or those composed of chitine, beautifully clear,
and fit for observation. Without this aid it would be im-
possible to resolve the structure of these minute animals.
The little Sword-bearer, like the Brachionus, carries its
eggs attached to the hinder part of its body, for some time
after they are discharged; the minute green oval bodies
that you see sticking to the side of this specimen, are not,
however, eggs, but parasitic animalcules (Colacium vesicu-
losum), which very frequently infest this species, adhering
to various points of the shell, and even to the sword-fins.
What I have nowto submit for your examination is one
of the rarest species of the class, and certainly not the
least singular in its form. It is the tripod Wheel-bearer
(Actinurus Keptunius). When fully extended, its length
exceeds that of almost every other species, for it reaches
about one-twentieth of an inch ; but its extreme thread-
like slenderness precludes the unassisted eye from taking
cognizance of it, as its thickness, even when greatest, is
not more than one six-hundredth of an inch.
From this excessive length and tenuity, the appearance
of the creature is very remarkable. It may be likened to
a cylindrical tube, out of which protrude a great number
of draw-tubes from both extremities, principally the pos-
terior one. Those in front terminate in an oval proboscis,
which, having a sort of ringer at its extremity, and two
eyes, with an antennal tube projecting obliquely back-
wards, presents, when viewed laterally, a strong resem-
WIIEEL-BEARERS.
249
blance to the head of a rabbit, the antenna representing
the ears. In front, and just below this head-like proboscis,
is a double swelling, containing the rotatory organs, which
are small and seldom unfolded. The eyes are deep black ;
probably, as in the last example, a red of great intensity.
When the head is withdrawn, the
integument is very clearly seen to
be turned inwards. The body con-
sists of one long cylindrical tube,
which receives three or four short
joints to complete the abdomen ; at
the dorsal point of the extremity of
the last of these is the cloaca ; at
this part the diameter is already
very much attenuated ; but there
are eight or nine more joints which
constitute the foot, and these are of
extreme slenderness. Towards the
extremity, two processes are given
off behind, each consisting of a club-
shaped piece, with a slender bristle
at the tip. The foot terminates in three long, slender,
cylindrical, divergent toes, which are flexible, and com-
monly bent outward ; they are equal in thickness, and
truncate. These are often retracted in various degrees,
even when the foot is otherwise extended.
Owing to the slenderness of the body, the viscera are
greatly elongated. The mastax, as usual in this family,
consists of two hemispheres (each bearing two teeth, set
transversely, but converging to the centre) ; it is situated
at a considerable distance from the wheels, and is reached
by a long buccal funnel. The digestive canal is a long
sac, apparently undivided ; it originates directly from the
mastax, with, I think, two small basal glands ; its pos-
terior extremity becomes gradually tapered to the cloaca.
In the specimen we are examining, a small quantity of
TBIPOD WHEEL-BEAREB.
250 EVENINGS AT THE MICROSCOPE.
f?ecal matter of a yellowish-brown colour is collected in
two small masses, near the extremity. Along the under
side runs the ovary, which in this specimen contains two
long oval eggs in advanced development; from their
transparent brightness, I suspect the young are produced
before birth. I think I can detect a contractile bladder,
but am not certain.
The dorsal region of the trunk is marked with strong
rugged lines running longitudinally; these look like corru-
gations of the integument, but I incline to think them the
strongly developed muscles for the retractation of the foot.
Muscles are seen running through the joints of the foot,
until they can no longer be traced, from their tenuity.
The viscera can be detected with difficulty, partly owing
to the longitudinal muscles, which are so strong and close,
and partly from the incessant contraction and elongation
of the parts, which drive the internal organs hither and
thither. It refuses, you see, to swallow carmine, which
might have assisted us.
This singular animal is lively in its motions, especially in
the protrusion and retractation of the extremities. These
are constantly alternating, and a very curious sight it is to
see the immense length of foot suddenly thrust forth from
the body, in which it has been completely hidden, the
starting out of the horizontal processes, and the diverging
of the long toes, as these are successively uncovered. The
latter do not seem to be often used as instruments of pre-
hension or adhesion. Indeed, the animal does not appear
very much given to change of place, but lies in the water,
alternately contracting and elongating. Frequently, as the
foot is thrust out, the body is made to bend forward so as
to form a right angle (see the engraving, in which the
animal is thus represented at a ; b represents it when the
head is rotating, but the foot is almost wholly withdrawn
within the body ; in which state the resemblance to a
telescope, or to a nest of glass tubes, is striking).
WHEEL-BEARERS. 251
The last specimen of this class of tiny favourites that I
shall show you is one of more than ordinary beauty. It
is the Two-lipped Tube-wheel of the Hornwort (Limnias
ceratophylli). Hitherto we have seen such examples as
have the power of freely swimming from place to place at
pleasure ; but there is a considerable group, of which this
is a member, which are permanently stationary, being
fixed for life to the leaves or stems of the vegetation that
grows under water. The stiff and spinous whorls of the
Hornwort (Ceratophyllum demersum), that grows com-
monly in sluggish streams and pasture-pools, is a favourite
resort of the species, but it is not confined to any one
plant. Here, for instance, it has chosen as the site of
its residence the much-cleft leaves of the Water Crow-
foot (Ranunculus aquatilis) ; those leaves, I mean,
which, growing wholly under the water, are divided into
a multitude of slender finger-like filaments, so different
from those which float on the surface, and which are
merely notched.
You can readily find the Tube-wheels by the aid of a
pocket lens, and even with the naked eye when you have
seen one or two. By holding up this phial, in which a
little plant of the Crowfoot is growing, and searching, with
the lens, the window being in front of you, the filaments,
one by one, you will readily perceive, here and there,
little shining objects standing up or projecting in various
directions from the surface of the leaves. The colony is
rather numerous in this case, and we shall have no diffi-
culty in selecting our specimens.
On this filament, which I have seized with the tips of
a pair of pliers, I can see at least half-a-dozen of the
little parasites. This, then, I will nip off from the
plant, and put it with its tiny population into the live-
box. Here it is ready for examination.
Several of the animals are in the field of view ; but we
will look at one at a time. A long narrow tube, slightly
252
EVENINGS AT THE MICROSCOPE.
widening at the mouth, is affixed by the lower extremity
to the slender filaments of water-grass, crowfoot, &c. It
is about one fifty-fifth of an inch in length, pellucid, but
tinged with brownish yellow. It appears to be of a gela-
tinous texture, and is covered with foreign substances,
such as decaying animal or vegetable mat-
ters, which adhere to its surface. From
the mouth of the tube protrudes a trans-
parent colourless animal, the head of which
^ is rounded, with the extremity pursed up.
Suddenly it unfolds its flower-like wheel,
which consists of two broad nearly circular
lobes united, the margin of which is set
with strong cilia, much resembling those
of the last species.
Each cilium appears to be curved, and
to be thickened at the middle — the optical
expression of the ciliary wave ; and the
effect of the rotation, as each seems to
pursue its fellows around the circular
course down the dividing sinuosity, up the
opposite sides, and round the margin again,
is very striking. The cilia at the front
^^ are interrupted between the lobes. In
H the centre of each lobe is a broad plate,
surrounded by a bright ring, and crossed
by radiating lines, which also extend to-
wards the ciliated margin ; probably these are muscular
filaments. The funnel is between the lobes, and leads by
a short oesophagus, or gullet, to a bulbous transparent
mastax, in which are seen jaws that wTork on each other.
Below this is a long capacious sac, without convolutions
or constrictions, but apparently granular in its texture.
The alimentary canal is bent upwards through the whole
length, terminating in an orifice behind the rotatory organ ;
for though I have not traced it when empty, I have seen
TWO-LIPPED
TUBE-WHEEL.
WHEEL-BEARERS.
253
the faecal matter driven rapidly upward as through a
canal, until the mass was discharged just behind the
sinuous cleft. On our mixing carmine with the water, the
effect is very striking; the particles, whirled round in two
circular vortices, are poured in an accumulated torrent
through the sinuosity, and over the elevation at the front
of the head. We presently perceive a slender line of
crimson passing down below the mastax, which indicates a
slender stomach-tube there ; and, after a while, a little ball
of the same pigment accumulates, and is seen resting a
little lower down. This, then, indicates the form and
position of the stomach; it must be a very slender canal,
terminating in a small rounded bag, at about one-third of
the distance from the mastax to the base of the tube. The
lengthened sac which you see is the ovary, from which the
eggs are discharged into the lower part of the case.
WHEELS OF TUBE-WHEEL.
The mouth needs a little explanation in detail. As
you see it, you probably discern little resemblance in its
parts to the same organ in Braclrionns, and yet essentially
it is formed of the very same parts; and as it is very
instructive to observe the modifications, in different
animals, of a common model of any particular organ, it
will be worth while to devote a few minutes' careful
observation to this structure before us, especially as it is
here seen with more than usual brilliancy and clearness.
The mastax, then, which you see in the centre of the
254 EVENINGS AT THE MICROSCOPE.
animal, just below the level of the beautiful flower-like
wheels, consists as usual of three sub-globose lobes; one
on each side appropriated to each malleus, and the third
descending towards the ventral aspect, which envelops
the incus. The mallei are more intimately united to the
rami of the incus than in the former type, each uncus
forming, with its ramus, a well-defined mass of muscle,
inclosing the solid parts, and in form approaching that
of a quadrant, or fourth part of a circle; two flat faces
opposing and working on each other. Across the upper
surface of the mass the uncus is stretched, as three long-
parallel fingers arched in their common direction, and
imbedded in the muscular substance; their points just
reaching the opposite face of the ramus, and meeting the
points of the opposite uncus, when closed. The manu-
brium is much disguised, by being greatly dilated trans-
versely, forming three bow-like loops of little solidity,
to the chord of which the fingers are soldered, not arti-
culated. The surface of the dense muscular mass disjDlays
stria3, or streaks, parallel to the fingers, and, as it were,
continuing their number towards their dorsal extremity,
becoming fainter till they are imperceptible. These stripe
do not disappear when the muscular parts are dissolved
by potash; and hence I infer the existence of a delicate
investiture of solid substance similar to that of the
teeth, ifec, inclosing the muscular mass.
The incus, which cannot be separated from the mallei,
thus consists of two portions, corresponding to the rami
in Brachionus, &c, each of which forms the lower part of
the mass just described. At the ventral extremity they
are articulated to a slender fulcrum, which is a little
bent downward. The solid framework of each ramus
sends off from its inferior surface a slender curved process,
which is connected with the extremity of the fulcrum.
The action of this apparatus is as follows : — The ciliary
vortices produced by the waves of the coronal disk, pass
WHEEL-BEARERS. 255
together through the upper sinus, and are hurled in one
stream along the centre of the face, nearly to the project-
ing chin. Here is placed the orifice of the buccal funnel,
a perpendicularly descending tube of considerable width,
slightly funnel-shaped at the top, the interior surface of
which is strongly ciliated. It descends straight upon the
mastax, over the part where the unci unite. But, just
above this point, there are two valves projecting from the
walls of the tube, also well ciliated. These can be brought
into contact, or separated in various degrees, at will,
and, being very sensitive, they regulate the force of the
inflowing current, and doubtless exclude hurtful or use-
less substances. The current now flows along the two
rami of the incus, as I have already described; and,
passing between their separated points, descends into
the oesophagus, a slender duct opening beneath them,
and leading to the digesting stomach.
As this current passes, the manducatory apparatus acts
upon the particles of food which it brings in its course.
The quadrant-shaped masses approach each other and
recede, with a rapid rolling movement, in the direction of
the curvature of the mallei; while, at the same time, the
rami of the incus open and close their points, rise and
sink, and occasionally perform a kind of shovelling action.
The points of the fingers of the unci, meeting each other,
doubtless pierce and tear the Infusoria swallowed, and
the striated faces bruise, squeeze, and grind them down.
AVhen the muscular investment is dissolved away by
potash, the essential identity of the whole structure with
that of the type already described becomes abundantly
evident. Even the mallei, which in some aspects present
difficulty, when viewed vertically, are but little changed ;
the fingers are parallel instead of divergent, and the
handle-like character of the manubrium is lost; but
three areas, inclosed by loops or carina? of solid substance,
reveal their true nature.
256 EVENINGS AT THE MICROSCOPE.
We will now see if we can separate the animal from its
tube, so as to examine its lower parts. By a gentle pres-
sure upon the bottom of the tube with the edge of a pen-
knife, which I bring to bear upon it by the aid of this
simple microscope, the creature is induced to wriggle out
of his case. Replacing now the cover of the live-box,
and placing it again on the stage of the compound micro-
scope, we" see that the lower part of the body forms a foot
analogous to that of a Brachionus, covered with ring-like
wrinkles, and separated from the body by an abrupt con-
striction and diminution of the diameter. At the very ex-
tremity there is a sort of sucking-disk, by which we may
presume the hold of the animal upon the plant is main-
tained. No organic connexion subsists between the foot
and the tube; for the latter is not an essential part of the
animal, though absurdly called a lorica by Ehrenberg, but
only an accumulation of mucus successively exuded from
the body, and thrown off in the form which it possesses
by the contractions and other movements of the body.
But see ! the poor naked creature is writhing in con-
tortions, which become more and more convulsive and
spasmodic: and now it evinces great rigidity in these, till
the body has become almost shapeless, portions of the
surface being here and there violently forced out into
projections, and the foot strongly curled up. The only
signs of life that now remain are the occasional fitful
workings of the jaws. Are we then to suppose that the
shelter of the gelatinous case is needful to its continued
existence % or did I inflict a mortal injury upon it when I
laid the edge of my penknife upon its lower part to drive
it forth % Most probably the latter is the true solution.
Out of the colony that remains, we will now select
another specimen, with ripening eggs, in order to watch
the development of the young. Here is one with three
eggs lying obliquely in the tube, one of which is already
showing the impatient movements of the embryo within.
WHEEL-BEARERS. 257
Ha ! now the egg-shell has burst, and the little creature
escapes from its prison, and quickly makes its way to the
mouth of the parent-tube. Now it is free, and swims
away rapidly, in a giddy, headlong manner. It is quite
unlike its mother ; for its form is trumpet-shaped, re-
sembling that of a Stentor with a wreath of cilia around
the head, interrupted at two opposite points : the central
portion of the head rises into a low cone. There is as
yet no trace of the beautiful double-petalled flower.
It has been whirling giddily about the live-box for
about a quarter of an hour, but now it begins to manifest
tokens of weariness; or rather the time is approaching
for it to select a place of permanent sedentary abode.
Its motion is sensibly retarded : it now and then adheres
to the glass momentarily, by its foot, and moves forward
by successive jerks, not proceeding more than its own
length at a time ; and this apparently with effort.
The periods of its remaining stationary become longer,
so that you may suppose it finally settled twice or thrice,
before its wanderings are quite over, some shock or
alarm sending it off to a little distance again.
At length it wanders no more; its foot holds fast to
the glass, and its movements are confined to whirlings
round and round on this as a pivot, and to sudden con-
tractions of length. Presently we see a very delicate
film surrounding the point of attachment; — the first
rudiment of the tube, a ring of mucus thrown off from
the skin, and pressed down to the foot by the contrac-
tions of the body. Meanwhile, the ciliary crown is
dividing itself into two, and now we see already the
essential form and appearance of the mature animal,
every moment developing its perfection.
258 EVENINGS AT TIIE MICROSCOPE.
CHAPTER XV.
WORMS.
An examination of the diverse modes in which locomotion
is performed among animals, and the various organs and
modifications of organs that subserve this important pur-
pose, would form no uninteresting chapter in natural
history. You have two feet ; your dog has four ; in the
bird, two of these are converted into wings, with which it
rises into the air; in the fish all of them are become fins,
with which it strikes the water. But it is in the inverte-
brate classes that we discover the strongest variations.
The Poulpe "flops" awkwardly but vigorously along, by
the alternate contractions and expansions of the web that
unites its arm; the Snail glides evenly over the herbage
by means of its muscular disk; the Scallop leaps about by
puffs of water driven from its appressed lips; the Lobster
shoots several yards in a second by the blow of its tail
upon the water ; the Gossamer Spider floats among the
clouds upon a balloon that it has spun from its own body ;
the Centipede winds slowly along upon a " hundred" pairs
of feet ; the Beetle darts like an arrow upon three ; and
the Butterfly sails on the atmosphere with those painted
fans which are properly "aerial gills." How elegantly
does the Planaria swim by the undulation of its thin
body, and the Medusa by the pumping forth of the water
held within its umbrella ! How wondrously does the
Echinus glide along the side of the tank on its hundreds
of sucking-disks ! How beautiful, and at the same time
how effective, are the ciliary wheels of the Brachionus !
worms. 259
I am now going to show you some other examples of
travelling machinery, in an humble and despised, but far
from uninteresting, class of animals, — the Worms. Here
is an Earth-worm upon the garden-border. With what
rapidity it winds along, and now it pokes its sharp nose
into the ground, and now it has disappeared ! If your
eye could follow it, you would see that it makes its way
through the compact earth not less easily nor less
rapidly than it wound along the surface. If you take
it into your hand, you perceive no feet, wings, fins, or
limbs of any kind ; only this long cylinder of soft flesh,
divided into numerous successive rings, and tapering to
each extremity. The very snout which you saw enter
so easily into the substance of the soil, is no hard bony
point, but formed of the same soft yielding flesh as the
other parts. And yet with no other implement does the
lithe worm penetrate wdiithersoever it will through the
ground. How does it effect this 1
The fineness of the point to which the muzzle can be
drawn is the first essential. This can be so attenuated
that the grains of adherent soil can be readily separated
by it ; when its action becomes that of the wedge. The
body being drawn into the crevice thus made, the particles
are separated still farther. Now another provision comes
in; the whole surface of the skin secretes and throws off
a quantity of tenacious mucus or slime, as you will imme-
diately perceive if you handle the Worm ; this has the
double effect of causing the pressed particles of soil to
adhere together, and then to form a cylindrical wrall, of
which they are the bricks, and the slime the mortar; and
also of greasing, as it were, the whole interior of the
burrow or passage thus made, so that the Worm can
travel to and fro in it without impediment ; while the
fact that the slime is continually poured forth afresh
prevents the least atom of earth from adhering to its
body. This you have doubtless observed, or may observe
« 9
2 GO EVENINGS AT THE MICROSCOPE.
in a moment, if you will take the trouble to thrust a
spade into the ground, and give it two or three shakes.
You will presently see on all sides the alarmed Earth-
worms coining swiftly to the surface, and will notice
how perfectly sleek and clean they are.
But these contrivances are only accessories : we have
not yet discovered the secret of the easy movement. The
mere elongation of the snout is no explanation of the
disappearance of the Worm in the burrow ; for you will
naturally and reasonably say that this elongation cannot
extend beyond a certain limit; and what then? Xo
further progress can be made unless the hinder parts of
the body are, by contraction, drawn up towards the
elongated front ; — but what holds the front in place
meanwhile 1 Why, when the muscles contract, does not
the taper, wedge-like muzzle slip back, and lose the
ground it had gained 1
This we will now look at. I take up this Worm, and
put it into a narrow glass cell, where we may watch its
movements. It presently begins to elongate and contract
its body vigorously, apparently alarmed at its unwonted
position ; and the mucus is thrown off in copious abund-
ance. We apply a low microscopic power to it, and catch
glimpses, now and again, as it writhes about, of a number
of tiny points protruded and retracted, with great regu-
larity, through the skin. Its mobility precludes our
discerning much more than that these points are very
numerous, that they are arranged in four longitudinal
lines, running along the ventral side of the animal, — two
lines on each side, — and that in each line there is a point
protruded from each of the many rings of which the
Worm's body is made up.
In order to see a little more of these organs we must
sacrifice a Worm ; having killed it, and divided the body
in the middle, I cut off, with sharp scissors, a small
transverse portion, say two or three rings, and press the
WORMS. 261
fragment between plates of glass. Now, with a higher
magnifying power, we discern in the midst of the trans-
lucent flesh the points in question. They are not, how-
ever, single; but each protrusile organ consists of a pair
of transparent, brittle, glassy rods, shaped like an
italic J] of which the recurved points are directed back-
wards when thrust out from the skin.
The mode in which these assist the progression of the
Worm is well described by Professor Rymer Jones.
" The attenuated rings in the neighbourhood of the mouth
are first insinuated between the particles of the earth,
which, from their conical shape, they penetrate like a
sharp wedge ; in this position they are firmly retained by
the numerous recurved spines appended to the different
segments ; the hinder parts of the body are then drawn
forward by a longitudinal contraction of the whole ani-
mal ; a movement which not only prepares the creature for
advancing further into the soil, but, by swelling out the
anterior segments, forcibly dilates the passage into which
the head had been already thrust : the spines upon the
hinder rings then take a firm hold upon the sides of the
hole thus formed ; and, preventing any retrograde move-
ment, the head is again forced through the yielding
mould ; so that, by a repetition of the process, the animal
is able to advance with the greatest apparent ease through
substances which it would at first seem utterly impossible
for so helpless a being to penetrate." *
Implements analogous to these are found in most of the
animals of the class Annelida, f to which the Earth-worm
belongs. But in this creature you see them in their sim-
plest form : it is to the aquatic Worms that you must look
if you wish to see the amazing diversity, complexity, and
delicacy of these organs. In these there are one or two
* "Gen. Outline," 202.
t From the Latin annellus, a little ring. A large class of animals
known under the common name of Worms.
262 EVENINGS AT THE MICROSCOPE.
pairs of "feet" on each ring, consisting of wart-like pro-
minences, which are perforate and protrusile, and through
the middle of which work a number of bristles (setce),
arranged in a radiating pencil, something like the hairs of
a paint-brush. In this transparent and colourless little
Nais from fresh water, you may see their form and
arrangement; in complexity they present an advance
upon the Earth-worm, for here there are some seven or
eight bristles in each pencil,
which radiate in the same
plane, and are graduated in
length ; they are very slender,
bent at the tip, and as trans-
parent as if drawn out of spun
glass. It is interesting to ob-
serve with what lisjhtnin^-like
FOOT OF NAIS. °
rapidity they are thrust out
and withdrawn in constant succession, as the body is
ever lengthening and shortening.
Let us exchange this little fresh- water Worm for a
marine one. Here is a Polynoe, a curious genus, very
common under stones at low water on our rocky shores.
It is remarkable on several accounts. All down the back
we discover a set of oval or kidney-shaped plates, which
are called the back shields {dorsal elytra) ; these are flat,
and are planted upon the back by little foot-stalks set on
near the margin of the under surface ; they are arranged
in two rows, overlapping each other at the edge. These
kidney-shaped shields, which can be detached with slight
violence, are studded over with little transparent oval
bodies, set on short foot-stalks which are perhaps delicate
organs of touch. The intermediate antennae, the tentacles,
and the cirri, or filaments of the feet, are similarly fringed
with these little appendages, which resemble the glands
of certain plants, and have a most singular appearance.
If we remove the shields, we discover, on each side of the
worms. 263
body, a row of wartlike feet, from each of which project
two bundles of spines of exquisite structure. The bundles,
expanding on all sides, resemble so many sheaves of
wheat ; or you may more appropriately fancy you behold
the armoury of some belligerent sea-fairy, with stacks of
arms enough to accoutre a numerous host. But if you
look closely at the weapons themselves, they rather re-
semble those which we are accustomed to wonder at in
missionary museums, — the arms of some ingenious but
barbarous people from the South Sea Islands, — than such
as are used in civilised warfare. Here are long lances,
made like scythe-blades, set on a staff, with a hook at the
tip, as if to capture the fleeing foe and bring him within
reach of the blade. Among them are others of similar
shape, but with the edge cut into delicate slanting notches,
which run along the sides of the blade like those on the
edge of our reaping-hooks. These are chiefly the weapons
of the lower bundle ; those of the upper are still more im-
posing. The outmost are short curved clubs, armed with
a row of shark's teeth to make them more fatal ; these
surround a cluster of spears, the long heads of which are
furnished with a double row of the same appendages, and
lengthened scimitars, the curved edges of which are cut
into teeth like a saw. Though a stranger nri^ht think I
had drawn copiously on my fancy for this description, I
am sure, with your eye upon what is on the stage of the
microscope at this moment, you will acknowledge that the
resemblances are not at all forced or unnatural. To add
to the effect, imagine that all these weapons are forged
out of the clearest glass instead of steel ; that the larger
bundles may contain about fifty, and the smaller half as
many, each ; that there are four bundles on every seg-
ment, and that the body is composed of twenty-five such
segments ; and you will have a tolerable idea of the
garniture and armature of this little Worm, that grubs
about in the mud at low-water mark.
264 EVENINGS AT THE MICROSCOPE.
Should it ever be your fortune to fall in with a species,
of Sea-mouse (Aphrodite liystrix), which inhabits our
southern coast a little way from the shore, you may be
delighted and surprised with a modification of these
organs, which exhibits a more than ordinarily obvious
amount of creative forethought and skill. I will describe
them in the words of the learned historians of these
animals, MM. Audouin and Milne-Edwards : —
" The feet are divided into two very distinct branches,,
the lower of which is large, conical, of a yellowish-brown
hue, and much shagreened on the surface. The upper
branch is much less salient than the lower. We observe
at the foot of the dorsal shields two bundles of rigid
bristles : the one, expanded like a fan and applied upon
the shields, is fixed immediately outside the insertion of
those organs; the bristles which compose it are awl-
shaped, without teeth, slightly curved, and directed in-
wards and backwards ; their colour is a clear brown,
with golden reflections. The second bundle is inserted
more externally, on a tuberculous foot-stalk, and points
horizontally backwards and outwards. The bristles which
enter into its composition are very long, very strong, and
terminated by a lance-shaped point, of which the edges
are garnished with teeth curved backwards towards the
base. These are veritable barbed arrows, having the
extremities sometimes exposed, but often concealed in a
sheath which is formed of two horny pieces, capable of
opening and of closing again upon them.
" The use of these two valves it is not difficult to detect.
They protect the points of the arrow, and permit the
Aphrodite to receive them again into its body unharmed ;
whereas, without this precaution, the tissues which they
traverse would be cut and mangled. But when these
weapons are deeply plunged into a foreign body, as into-
the soft flesh of those animals which annoy the Worm,
since the sheath does not penetrate with them but folds-
worms. 265^
back, it follows that their teeth are inserted without any
protection, and that on account of their backward direction
they can be withdrawn only with great difficulty; thus,
in most cases, the dart becomes broken; but the animal
is furnished with so great a number, that these losses
are scarcely felt, and there remain to it amply sufficient
for its defence in all contingencies."*
You will have noticed that the learned French zoologists
seriously countenance the notion that these exquisitely
elaborate organs are weapons of offence. But in this I
think they are in error, misled by the resemblance, already
alluded to, which the parts bear to weapons of human
construction. The manner in which they act as imple-
ments of locomotion has been beautifully demonstrated
by Dr. Williams in the ISTereidous Worms, of which he
observes that in nearly all species the feet are constructed
with express reference to progression on solid surfaces.
In many instances, the bristle is compound, consisting of
a staff with a variously armed point or blade jointed to its
extremity. "Viewed by the light of mechanical prin-
ciples, nothing cau be so obvious as the reason why the
setce in these, as in nearly all other Annelida, are jointed.
If they consisted of rigid, unbending levers, it is manifest
that they would prove most awkward additions to the
sides of the animals; if fixed too deeply in the surrounding
soil, they would not act at all as levers ; if too superficially,,
the Worm would be compressed in its tube at the
moment when the setce of the opposite feet would meet
in a straight line. These difficulties are effectually and
skilfully obviated by the introduction of a joint or a
point of motion on each seta. This is one instance
among many which the eye of the mechanician would
detect in the organisation of the Annelida, in which
Nature takes adroit advantage of mechanical principles
in the attainment of her ends." t
* " Litt. de la France," ii. 71. + " Kep. on Brit. Annelida," 211..
266 EVENINGS AT THE MICROSCOPE.
Look now, in illustration of these principles, at the
bristle-feet of this beautiful green Phyllodoce. No doubt
you have often seen it in the little hollows of our rocky-
ledges, and especially on beds of young mussels; and
probably you have admired the elegant ease with which
its lithe and tortuous body writhes and winds, like a bit
of green silken cord, in and out among the compactly
crowded shells. You have wondered, too, at the difficulty
which attends the attempt to take it up, not on account
of the rapidity of its motions, but because of the extreme
slenderness and slipperiness of the subject, and of the
power which it possesses of insinuating itself into the
smallest crevice.
The foot in this genus has but a single branch, and a
single pencil of bristles, which is placed between the flat
swimming leaf that ornaments each segment and the lower
cirrus. The bristles are of the compound jointed form,
but the joint is fixed in a peculiar manner. The basal
portion is drawn out into a very slender, long, straight
shaft, terminating in a knob somewhat resembling the end
of a limb-bone. This is slit in one direction to receive the
terminal piece, which is shaped somewhat like a lance-
head, and is inserted into the slit exactly as a knife-blade
is fixed into the haft. The head is in fact a knife-blade,
with a thickened back and a very thin edge, which is
notched into teeth of the most exquisite delicacy. The
blade is slightly curved, and drawn out into a long acute
point; and the w^hole bristle is formed out of an elastic
horny substance (probably chitine), that rivals in trans-
parency and brilliancy the purest flint-glass.
I might adduce a vast variety of examples of these
organs in the Marine Worms, all of which would charm
you by their elegance and by their extreme diversity; but
I have other things to show you in this interesting class
of animals, which fortunately are so common on all our
shores that you will have no difficulty in procuring plenty
worms. 267
of specimens for your private observation and study.
And if you need intelligent guidance you cannot have
.a better mentor than Dr. Williams, whose admirable
"Report on the British Annelida" I have just cited.
Before we dismiss our little Phyllodoce to its home in
the aquarium, we must try to get a sight of its pretty
mouth. The Worms are somewhat wayward in displaying
this part of their charms, sometimes exposing it at in-
tervals of a second or two for very many times in succes-
sion, at others sullenly keeping it closed; and no efforts
that I am aware of on our part will induce the display;
we must await their pleasure. It is, in fact, a turning of
the throat inside out. In most of the Worms the head is
minute; and what seems to be the mouth is but the orifice
from which the throat or proboscis is everted. In the
Phyllodoces this organ is a great muscular sac, in some
species equalling in length one-fourth of the whole body.
Ha ! there it appears ! What a chasm yawns in the
under-side of the head, as the interior begins rapidly to
protrude, turning inside out as it comes forth, like a living
stocking, until it assumes the form of an enormous (com-
paratively enormous, of course,) pear-shaped bag, the
surface of which is beset with a multitude of secretins:
warts or glands, somewhat like the papilla? which stud the
tongue in higher animals ! The extremity, which is per-
forated, is surrounded by a muscle, by means of which it
contracts forcibly on whatever it is applied to, and thus
holds it firmly, while the re-inversion of the sac drags it,
if suitable, into the body to be digested.
But this huge proboscis disappears as rapidly and as
wonderfully as it was revealed. Commencing at what is
now the outer extremity, which is quickly tumed-in, the
whole swiftly returns to its cavity in the inverse order
to that in which it was extruded; and now that it is all
engulfed, we marvel that so vast a sac can be packed
away in so slender a case.
268 EVENINGS AT THE MICROSCOPE.
In this instance the armour of the proboscis is feeble;
but we have species which are very elaborately armed.
There is a minute species of Lombrinereis, which com-
monly appears in our aquaria after they have been some
time established, and breeds in vast numbers on the
fioccose matter that clogs the bottom and sides. In this
tiny Worm there is a formidable array of jaws, resembling
black hooks, which we may discern through their pellucid
tissues, snapping and cutting viciously like so many pairs
of hooked scissors. Though I have often had this little
species in my tanks in copious abundance, I regret to
say I cannot find any at this moment for our examination,,
and shall therefore content myself with translating for
you MM. Audouin and Milne-Edwards' description of
the jaws, as they appear in a closely-allied form, but of
far greater dimensions, Eunice.
" The proboscis is not very protrusile; when it is with-
drawn its external orifice is longitudinal, and the jaws
are fixed on each side, all facing the medial line. When it
is projected, however, the two margins of the longitudinal
cleft become transverse in separating, and the jaws follow
the same movement, and diverge in the ratio of their for-
wardness. A kind of lower lip which is affixed to the
under side of the proboscis is composed of two horny
blades united towards their front extremity, and prolonged
behind into points. The jaws are to the number of seven ;
three on the right and four on the left ; the two upper
ones are perfectly alike, and mutually opposed; they are
large, narrow, pointed, re-curved hook-wise at the tip,
and jointed at their hinder ends on a double horny stem
shorter than themselves. The second pair of jaws are
large, broad and flat, mutually alike, and jointed on the
lower side of the first pair; . . . their internal edge is
straight and cut into deep teeth. The third pair are
small, thin, concave, and notched ; they are affixed by
their inferior edge outside and in front of the second pair,
which they conceal during repose. Finally, the super-
WORMS.
2G9
numerary jaw, which is found on the left side only, is
small, semicircular, toothed, and placed between the
second and third pairs. All these pieces are surpassed
by the margin of the proboscis, which is often hard and
black."*
From this complex and formidable mouth we will pass
to one of quite another form, not less effective, perhaps
more formidable, but ordained by the goodness of God to
be a most valuable agent in the relief of human suffer-
ing. I mean the medicinal Leech, of which we can readily
procure a specimen from our friend the apothecary.
Here it is. There is no protrusile proboscis, but the
throat is spacious, and capable of being everted to a slight
degree. The front border of the mouth is enlarged so as
to form a sort of upper lip, and this combines with the
wrinkled muscular margin of the lower and lateral portions
to form the sucker. With the dissecting scissors I slit
down the ventral margin of the sucker, exposing the
whole throat. Then the edges being folded back, we see
implanted in the walls on the dorsal region of the cavity
three white eminences of a cartilaginous texture, which
rise to a sharp crescent-
shaped edge ; they form
a triangular, or rather a
triradiate figure.
Now, if you recollect,
this is the figure of the
cut made in the flesh
wherever a Leech has
sucked, as it is of the
scar which remains after
the wound has healed.
For these three little eminences are the implements with
which the animal, impelled by its blood-sucking instincts,
effects its purpose. But to understand the action more
perfectly, we must use higher powers.
* " Litt. de la France," ii. 138.
THROAT OF LEECH LAID OPEV.
270
EVENINGS AT THE MICROSCOPE.
I dissect out of the flesh, then, one of the white points,
say the middle one, and laying it in water in the compres-
sorium, flatten the drop, but use no more pressure than
just enough for that. Now I apply a power of 150 dia-
meters, and we will look at it in succession. You have
under your eye a somewhat pellucid mass, of an irregular
oval figure, and of fibrous texture, one side of which is
thinned away apparently to a keen edge of a somewhat
semicircular outline. But along this edge, and, as it were,
imbedded into it for about one-third of their length, are
set between seventy and eighty crystalline points, of highly
refractive substance, resembling glass. These points gra-
dually decrease in size towards one end of the series, and
at length cease, leaving a portion of the cutting edge
toothless. At the end where they are largest they are
nearly close together, but at length are separated by spaces
equal to their own thickness. The manner in which they
are inserted closely resembles, in this aspect, the insertion
of the teeth in the jaw of a dolphin or crocodile.
But this appearance is deceptive. By affixing the little
jaw to the revolving needle, we bring the edge to face our
eye. It is not an edge at all ; but a narrow parallel-sided
margin of considerable breadth. And the teeth are not
conical points, as they seemed when we viewed them
sidewise, but
flat triangular
vV^W,^"A'&^ plates, with a deep notch in
8v\ ' ; \ \ ml I nlliil i I t^ieir l°wer ec^oe- Tnus tney
partly embrace, and are partly
inserted in, the margin of
the jaw.
Observe now how beauti-
fully this apparatus subserves
the purpose for which it is
intended. By means of its
sucker, the Leech creates a
vacuum upon a certain part of the skin, exactly like that
JAW OF LEECH (in part).
WORMS. 271
produced by a cupping-glass. The skin covered is drawn
into the hollow so far as to render it quite tight, by the
pressure of the surrounding air. Thus it is brought into
contact with the edges of the three jaws, to which, by
means of powerful muscles attached to them, a see-saw
motion is communicated, which causes the little teeth
soon to cut through the skin and superficial vessels,
from which the blood begins to flow. The issue of the
vital fluid is then promoted by the pressure around, and
so goes on until the enormous stomach of the Leech is
distended to repletion.
It has been suggested that this whole contrivance, with
the instinct by which it is accompanied, is intended for
the benefit of Man, and not of the Leech. Blood seems
to be by no means the natural food of the Leech; it has
been ascertained to remain in the stomach for a whole
twelvemonth without being digested, yet remaining fluid
and sound during the entire period : while, ordinarily,
such a substance cannot in one instance out of a thousand
be swallowed by the animal in a state of nature.
Whether this is so or not, — whether man's relief under
suffering was the sole object designed, or not, it was
certainly one object ; and we may well be thankful to
the mercy of God, who has ordained comfort through
so strange an instrumentality.
The progress of marine natural history, as studied in
the aquarium, has made our drawing-rooms and halls
familiar with a multitude of curious and beautiful creatures
which a few years ago were known only, and that very
imperfectly, to the learned professors of technical science.
Among the forms which embellish our tanks are several
species of Serpula, and Worms allied to it. The shelly
contorted tube which this painted Sea-worm inhabits, and
which it has built up around its own body, with stone
and cement which that body supplied, is well known to
you ; as is also the curious conical stopper with which it
272 EVENINGS AT THE MICROSCOPE.
closes up its bottle as with a cork, when safe at home,
and the lovely crown of gorgeously coloured fans which it
expands when it takes ("the air" T was about to say, but
rather) the water. You are familiar, too, with the light-
ning-like rapidity with which, while in health and vigour,
the Serpula, on the slightest alarm, retreats into his
fortress, taking care to clap-to the door after him. But
perhaps you have never had an opportunity of examining
the mechanism by which this rapid flight is effected.
As there are two distinct movements performed by the
Worm, — the slow and cautious and gradual protrusion,
and the sudden and swift retreat, — so there are two
distinct sets of organs by which they are performed.
Shall I sacrifice one from this fine group to demonstrate
the mechanism % Well, then, I carefully break the shelly
tube, and extract the worm uninjured.
Its form is, you perceive, much shorter and more
dumpy than you would have supposed from looking at
the tube ; and it is somewhat flattened, having a back-
and a belly-side. On the former there is a sort of shield,
the sides of which bear wart-like feet, — about seven
pairs in all, — which are perforated for the working of
protrusile pencils of bristles, similar in structure and in
function to those which we lately examined.
Here is one of the pencils extracted. To the naked
eye it is a yellowish body with a satiny lustre ; and this
effect depends upon the light being reflected from a
number of nearly parallel lines, — the staves of the spear-
like bristles,- — which the eye cannot resolve in detail.
A drop of the caustic solution of potash cleanses the
bundle from the fleshy matter which would otherwise
obscure the vision, and now I place it on the stage.
With this power of 400 diameters you see a multitude
— some twenty or thirty, or more — of very long, slender,
straight rods, of a clear yellowish horny substance, set
side by side, like a sheaf of spears in an armoury. Each
WOHMS.
273
one merges, at its upper end, into a sort of blade, which
is slightly bent, and which tapers to an exceedingly fine
point. But its chief peculiarity is that the blade has a
double edge, not like a two-edged sword, the edges set
on opposite faces, but on the same face, set side by side,
with a groove between them; and each head is cut with
the most delicate and close-set teeth, the lines of which
pass back upon the blade, as in our sickles.
PUSHING POLES OF SEBPULA.
These pencils of spear-like bristles are the organs by
which the protrusion of the animal is performed. Their
action is manifestly that of pushing against the walls of
the interior, which on close examination are seen to be
lined with a delicate membrane, exuded from the animal's
skin. The opposite feet of one segment protrude the
pencils of bristles, one on each side, the acute points and
teeth of which penetrate and catch in the lining mem-
brane; the segments behind this are now drawn up close,
and extend their bristles; these catch in like manner ;
then an elongating movement takes place ; the pencils of
the anterior segments being now retraced, they yield to
the movement and are pushed forward, while the others
are held firm by the resistance of their holding bristles ;
thus gradually the foreparts of the animal are exposed.
But this gradual process would ill suit the necessity of
a creature so sensitive to alarm, when it wishes to retreat.
We have already seen how, with the fleetness of a thought,
its beautiful crown of scarlet plumes disappears within its
T
274
EVENINGS AT THE MICROSCOPE.
stony fastness : let us now look at the apparatus which
effects this movement.
If you look again at this Serpula recently extracted,
you will find, with a lens, a pale yellow line running along
the upper surface of each foot, transversely to the length
of the body. This is the border of an exceedingly delicate
membrane; and on placing it under a higher power (say
600 diameters) you will be astonished at the elaborate
provision here made for prehension. This yellow line,
which cannot be perceived by the unassisted eye, is a
muscular ribbon, over which stand up edgewise a mul-
titude of what I will call combs, or rather sub-triangular
plates. These have a wide base ; and the apex of the
triangle is curved over into an abrupt hook, and then
this is cut into a number (from four to six) of sharp and
long teeth. The plates stand side by side, parallel to
each other, along the whole length of the ribbon, and
there are muscular fibres seen affixed to the basal side
of each plate, which doubtless give it independent motion.
I have counted 136 plates on one ribbon ; there are two
ribbons on each thoracic segment, and there are seven
such segments ; — hence we may compute the total
HOOKS OF SEBPULA.
number of prehensile comb-like plates on this portion of
the body to be about one thousand nine hundred, each
worms. 275
of which is wielded by muscles at the will of the animal ;
while, as each plate carries on an average five teeth,
there are nearly ten thousand teeth hooked into the
lining membrane of the cell, when the animal chooses
to descend. Even this, however, is very far short of the
total number, because long ribbons of hooks of a similar
structure, but of smaller dimensions, run across the
abdominal segments, which are much more numerous
than the thoracic. No wonder, with so many muscles
wielding so many grappling hooks, that the retreat is so
rapidly effected !
t 2
27G EVENINGS AT THE MICROSCOPE.
CHAPTER XVI.
SEA-URCHINS AND SEA-CUCCMBERS.
Peering about among the rocks to-day at low-tide, Z
found, on turning over a large stone, an object which;
though familiar enough to those who are conversant with
the sea and its treasures, would surprise a curious ob-
server fresh from the fields of Warwickshire. It is a ball,
perfectly circular, and nearly globular, — only that its
under part is a little flattened, — hard and shelly in its ex-
terior, which is, however, densely clothed with a forest of
shelly spines, each one of which has a limited amount of
mobility on its own base. On attempting to remove it, I
find that it adheres to the stone with some firmness ; and
that, on the exercise of sufficient force, it comes away with
a feeling as if something were torn, and I find that a mul-
titude of little fleshy points are left on the stone. Having
dropped my prize into a glass collecting-jar of sea-water,
I presently see that it is slowly marching up the side,
sprawling out on every side a multitude of transparent
hands, with which it seems to feel its way, and which are
evidently feet also, for on these it crawls along at its own
tortoise-pace. And I now see that it is the knobbed ends
of some of these feet which were torn away by my forcible
act of ejectment, and left clinging to the stone.
It was not the first time that I had seen the Sea-urchin
(Echinus miliaris) ; and I might have passed it by with
a feeling of satiated curiosity, had I not recollected our
evening's amusement. Oh, ho ! said I, what a fund of
microscopic entertainment is inclosed in this stone box !
SEA-URCHINS AND SEA-CUCUMBERS. 277
&So I brought it home, and now produce it as the text of
our conversazione.
Every part is a wonder; but we must examine each in
•order. Take the spines first.
As, using this triple lens, we examine these organs
• on the animal crawling at ease over the bottom of a
■saucer of sea- water, we see that each is a taper pillar,
rounded at the summit, and swelling at the base, where
-it seems to be inserted into a fleshy pedestal, on which
it freely moves, bending downward in all directions, and
■ describing a circle with its point, of which the base is
the centre. Each spine is for the greater portion of its
length of a delicate pea-green hue, but the terminal part
■ is of a fine lilac or pale purple. The whole surface
appears to be fluted, like an Ionic column, but this is an
illusion, as you will see presently.
I now detach one of the spines, cutting it off with fine-
pointed scissors as near the base as I can reach. I put it
with as little delay as possible into the live-box, and
examine it with a high power, say 600 diameters. Look
-at it. You see the ciliary currents very distinctly; and
t if you move the stage so as to bring the basal portion
.into view, you may discern even the cilia themselves,
very numerous and short, quivering with a rapid move-
ment. The currents are not longitudinal, but transverse,
and somewhat peculiar. The floating atoms which come
within their vortex are drawn in at right angles to the
axis of the spine, and are presently hurled away in the
same plane; forming a circle, whose plane is perpendicular
to the direction of the spine. The surface upon which
these cilia are set is a transparent gelatinous skin, of
extreme tenuity, stretched tightly over the solid portion,
which it completely covers, and studded with minute
oval orange-coloured grains.
The substance of which the spines are composed is best
seen by crushing a few of these organs into fragments.
278 EVENINGS AT THE MICROSCOPE.
We now see a texture beautifully delicate; they are
formed of calcareous substance as transparent as glass,
and reflecting the light like that material ; hard but very
brittle; clear and solid, with a fibrous appearance in
some parts, but in others excavated into innumerable
smooth rounded cavities which join each other in all
possible ways. It is to this structure that the spine
owes its strength, its lightness, and its brittleness.
This arrangement of the calcareous deposit in a sort of
glass full of minute inter-communicating hollows is very
peculiar, but it is invariably found in the solid parts of
this class of animals ; so that the experienced naturalist,
on being presented with the minutest fragment of solid
substance, would, by testing it with his microscope, be
able at once to affirm with certainty, whether it had be-
longed to an Echinoderm * or not. And this uniformity
obtains in all the diverse forms which the animals assume,
and in all the various organs which are strengthened
by calcareous deposits — Crinoid, Brittle-star, Five-finger,
Urchin, Sea-gherkin, or Synapta; ray, plate, spine,
sucker-disk, lantern, pedicellaria, dumb-bell, wheel, or
skin-anchor, — whenever we find calcareous matter, we
invariably find it honey-combed, and eroded, as it were,
in this remarkable fashion.
Dr. Carpenter has described this texture so well, that I
shall not apologise for quoting his words to you, especially
as you will have an opportunity here of testing their cor-
rectness, by personal observation. " It is," he remarks,
"in the structure of that calcareous skeleton, which pro-
bably exists, under some form or other, in every member
of this class, that the microscopist finds most to interest
him. This attains its highest development in the Echiniday
in which it forms a box-like shell, or ' test,' composed of
* From the Greek Ixlvog (echinos) a hedgehog, and dspfia (derma)
sMn. A name given to these animals from their bodies being generally
armed with spines.
SEA-URCHINS AND SEA-CUCUMBERS. 279
numerous polygonal plates joined to each other with great
exactness, and beset on its external surface with ' spines/
which may have the form of prickles of no great length,
or may be stout, club-shaped bodies, or, again, may be
very long and slender rods. The intimate structure of the
shell is everywhere the same; for it is composed of a net-
work, which consists of carbonate of lime, with a very
small quantity of animal matter as a basis, and which
extends in every direction (i.e., in thickness, as well as in
length and breadth), its areolae or interspaces freely com-
municating with each other. These 'areola?,' 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 texture may have either a remark-
able lightness and porosity, if the network be a very open
one, or may possess a considerable degree of compactness,
if the solid portion be strengthened. Generally speaking,
the different layers of this network, which are connected
together by pillars that pass from one to the other in a
direction perpendicular to their plane, are so arranged that
the perforations in one shall correspond to the interme-
diate solid structure in the next; and their transparency is
such, that when we are examining a section thin enough to
contain two or three such layers, it is easy, by properly
' focussing ' the microscope, to bring any one of them
into distinct view. From this very simple but very beau-
tiful arrangement, it comes to pass that the plates of
which the entire ' test ' is made up, possess a very con-
siderable 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." *
To return, however, to our spine. When we look at it
* ''The Microscope," 553.
280 EVENINGS AT THE MICROSCOPE.
laterally, the appearance is such that we cannot but firmly
believe, that it is grooved throughout with straight and
deep longitudinal furrows. But if we break off the same
spine transversely, and so exhibit it that the broken end
shall be presented to the eye, we perceive that there are
no grooves; but that the points in the circumference,
which seemed to be the summits of the ridges, which are
very narrow, are really lower than the intermediate spaces,
which we supposed to be the grooves, and that the surface
of these spaces is really convex in a slight degree.
The explanation of these contradictory appearances is
easily given. Meanwhile, however, they read an im-
portant lesson to the inexperienced microscopist, not to
decide too hastily on the character of a surface or a
structure, from one aspect merely. So many are the
chances of illusion, that the student should always seek
to view his subject in different aspects, and under vary-
ing conditions of light, position, &c.
It is by making a thin transverse section of a spine, —
cutting off a slice of it, to speak in homely phrase, — -that
we shall demonstrate the structure, which is very beau-
tiful. This is an operation requiring much delicacy and
practice, and implements for the special purpose ; and
hence it is best performed by professional persons, who
prepare microscopic objects for sale. You may see such a
section, however, on this slide ; but I do not know whether
the spine belongs to the species we are examining.
The whole central portion is formed of the sponge-like
calcareous matter, which, from the variously reflected and
refracted rays of light, appears nearly opaque, and of a
bluish colour by transmitted light. This structure sends
forth radiating points (making longitudinal ridges, of
course, in the perfect spine); and it is the opacity of these
points (or ridges) which reach the circumference, that
gives to the spine the appearance of being fluted. Indeed
it would be fluted if this were the entire structure; but the
SEA-URCHINS AND SEA-CUCUMBERS.
281
vBssbKsw
open space left between these projecting radii is filled
with the solid glassy matter, having, as we see, a convex
surface. This, however, from its perfect transparency, is
not seen when we look at the side of the spine, the eye
going down through the transparent matter to the bottom
of the space. The spine is, in fact, a fluted column of
spongy glass, with the grooves filled with solid glass.
We have not yet seen, however, the beautiful mechanism
appropriated to the movement of these spines. You can
hardly see this to advantage in
the living animal, but here is
the entire shelly box of a dead
Echinus, on which, while for
the most part the surface is
denuded of spines, a few dozen
remain sufficiently attached to
show what I wish to demon-
strate, viz. , the mode of articu-
lation. You observe that th«
whole globose shell is covered
with tiny knobs, differing in
size, and not set in very re-
gular, or at least not very ob-
vious, order, but showing a
tendency to run in lines from
;pole to pole of the globe. Giving attention to one of tlie
larger of these knobs, under a lens it is seen to be a hemi-
spherical eminence on the shell, the very summit of which
is crowned by a tiny nipple of polished whiteness, re-
sembling ivory. Xow if we carefully lift one of the still
remaining spines from its attachment, which in its present
•dried state is so fragile that the slightest touch is sufficient
for the purpose, we shall note that its base rests on this
tiny nipple ; and, on turning it up, and bringing the mag-
nifying power to bear upon its base, we see that this is
•excavated with a hollow, whose dimensions exactly corre-
SPINE OF ECHINUS.
Segment of Section.
282 EVENINGS AT THE MICROSCOPE.
spond with those of the nipple. It is indeed a true "ball-
and-socket" joint, like that of the human hip or shoulder,
and is surrounded by a capsular ligament to keep it in
place ; the muscles which sway the spine from side to side
and cause it to rotate being inserted outside the capsule
or case. Professor Edward Forbes calculates that upon
a large Echinus, such as this dried specimen of E. sphcera,
there are more than four thousand spines, every one of
which has the structure, the mechanism, and the move-
ments that we have been examining. Well may he say,
that " truly the skill of the Great Architect of Nature is
not less displayed in the construction of a Sea-urchin
than in the building up of a world ! "
To return now to our little E. miliaris, which has been
all this time coursing round and round his saucer, wonder-
ing, perchance, at the narrowness and shallowness of the
White Sea in which he finds himself. Again we peer, lens
to eye, over the bristling surface, and discern, shooting up
amidst the spines, and almost as thickly crowded as they,
multitudes of the tiny organs which have caused so much
doubt and discussion among naturalists. Midler, the great
marine zoologist of Denmark, who first discovered them,
thought them parasitic animals, living piratically upon the
unwilling Urchin, and accordingly gave them generic and
specific names. The term ])edicellaria, which he assigned
to his supposed genus, is that by which modern natu-
ralists have agreed to call them still, though the word is
not now used in a generic sense, since it is indubitably
established that they are not independent animals, but
essential parts of the Urchin itself. Miiller described
three distinct sorts, and I have added a fourth to the
number ; they are named P. triphylla, tridens, globifera,
and stereopliylla. They all agree in these particulars : —
That each has a long, slender, cylindrical, fieshy stem,
through the centre of which runs an axis or rod of calca-
reous substance ; that the base of the stem rests on the
SEA-URCHINS AND SEA-CUCUMBERS. 283
skin of the Urchin ; that on the summit is placed a head
consisting of three pieces, which are capable of being
widely opened and of being closed together, at least at
their tips; that the edges of these pieces, which come into
mutual contact, are furnished with teeth, which lock into
each other; that the head-pieces (like the stem) consist of
calcareous centres, clothed with flesh; that, besides the
opening and shutting of the head, the stem can be swayed
from side to side ; and that all these movements are spon-
taneous, and apparently voluntary. It appears that the
head-pieces close on any object presented to them, such
as the point of a needle, and hold with considerable force
and tenacity, so that the pedicellaria may be drawn out
of the wTater without relaxing its grasp.
Looking at one of the first-named kind, the pedicellaria
triphylla, of this Echinus miliaria, we see that it consists
of three broad and thick somewhat triangular pieces,
jointed into a head, set on a thickish stem of transparent
gelatinous fibrous substance, through which a slender core
of calcareous matter runs that looks fibrous and blue.
The three movable pieces or blades are convex externally,
concave internally ; thin in substance, furnished along
their opposite or concave sides with two longitudinal
ridges or keels, each of which is cut into the most beau-
tifully fine teeth, so that the edge of each ridge looks like
a shark's tooth ; the edges of the pieces are also similarly
toothed : these shut precisely into each other.
In the larger E. sphcei'a, the head-blades of this kind
have one stout central ridge, which is rounded and not
toothed. It forms the front of a great interior cavity
which opens by two orifices on each side of the column.
The movable pieces inclose a skeleton of calcareous
substance, glassy, colourless, and brittle, in which, ac-
cording to the plan I have already described, are ex-
cavated a multitude of oval cavities which form irregular
rows ; a central line runs down each piece, that is solid
-284
EVENINGS AT THE MICROSCOPE.
and free from cavities. This calcareous skeleton is
-encased in a gelatinous flesh, similar to and continuous
with that of the stalk.
This is the smallest kind, the head being about -=-Vth
of an inch in height.
Considerable modifications are found to exist in the
details of each form, in the relative proportions which the
parts bear to each other, and so forth ; so that two forms,
which in their extreme conditions widely differ, mutually
•approach, and appear to run into each other. This is
the case with the present, and with the form which I
-will now show you.
P. tridens is much larger than any of the other forms,
the movable head being about -^V ^h
of an inch in length, and the wdiole
organ about -^th of an inch. This
may be considered as essentially
P. trip/iylla, modified by the
blades being greatly drawn out in
length, and at the same time ren-
dered quite slender, so that they
may be called pins; they meet only
at the points, where they often
cross ; the spaces between the basal
parts being open. The inner edges
of these are notched with teeth as
in P. triphyUat of which those near
the tips are larger, and cut into
subordinate teeth of exquisite
minuteness.
We have here an opportunity
of seeing that the oval or square
markings, which are thickly placed
throughout the calcareous sub-
stance of the blades, are certainly cavities in it; for in
dhose examples in which the pins, which are very brittle,
HEAD OF PEDICELXARIA
TBIDENS.
SEA-URCHINS AND SEA-CUCUMBERS. 285-
are broken, the edge of the fracture is not evren, but jagged,
with holes exactly corresponding with the marks in
question; so that the structure is the same as that of the
spines and of all the other solid parts of the Urchin.
We will now examine some specimens of P. tridens,
treated with potash, which will enable us to see the calca-
reous support better. The head-blades expand at the base
into three-sided figures, each of the two interior sides of
which is indented with a large cavity, leaving a projecting,
dividing rid^e, armed with teeth somewhat remote from
each other. The one exterior angle is toothed in a cor-
responding manner, but the opposite angle appears plain.
The angle of one blade-base fits into the cavity of its-
neighbour ; and, so far as I have observed, when the two
edges thus overlap it is the toothed one that is on the out-
side. Looking from the circumference towards the centre -
of the head, it is the left angle that is toothed and external,
the right being plain and sheathed. This observation,,
however, applies only to E. miliaria j for, in the corre-
sponding organs of E. sphrera, both sides of the three-
cornered base appear untoothecl, except close to the-
bottom, where a deep notch indents each margin.
Viewed from beneath, the head assumes an outline
which is rondo-triangnlar; but yet such that each side of
the triangle has a very obtuse projecting angle in the-
middle, where the blade-bases meet each other. They fit
accurately, and each has a deep oblong cavity in its
bottom, which does not, as I conceive, communicate with
the interior.
By selecting one of these heads, which has been
divested of its fleshy parts by immersion in caustic pot-
ash, and then well cleansed by soaking in clean water,
and placing it under a low power of the microscope —
100 diameters, for example — with a dark ground, and the
light of the lamp cast strongly upon it by means of the
Lieberkiihn, or the side condenser, we shall have an object
2SQ EVENINGS AT THE MICROSCOPE.
of most exquisite beauty. The material has all the trans-
parency and sparkling brilliance of flint-glass, while the
elegantly-shaped pins, the perfect symmetry of the bases,
the arch which is lightly thrown across their cavity, the
minute teeth of the tips locking accurately into each
other, and the oval cavities in the whole structure set in
regular rows, and reflecting the light from thousands of
points, constitute a spectacle which cannot fail to elicit
your admiration.
P. globifera is formed on the same model as P. tripliylla,
but is more globose, and each piece appears to have a
deep cleft at the point, which does not extend to the inte-
rior side, where a thick ridge runs down from the point to
the base. At the summit of this ridge, in each of the three
divisions, there is set a strong acute spine, directed hori-
zontally inwards, so that the three cross each other when
the blades close, which they do energetically, — a formid-
able apparatus of prehension ! The stem is much more
slender than in P. triphylla, and the height of the head of
one of average size is only ^rd of an inch. It is peculiar
also in being slender throughout, and in having the
knobbed calcareous stalk extending up to the head, which
appears to work on it. In each of the other sorts the stalk
extends only through a part of the distance, above which
the investing fleshy neck becomes wider and empty.
But the internal structure is not quite the same as in
the others. The main portion of the head is composed of
gelatinous flesh ; the calcareous support being reduced to
that ridge which runs up the interior side of the blade.
This is somewhat bottle-shaped, with a bulbous base, and a
long slender neck, with two edges on the inner face, which
are armed with horizontal hooked spines, some of which are
double ; and the whole terminates in a sort of ring, formed
by the last pair of spines, which unite into the acute hori-
zontal point that I have already mentioned. The skeleton
is filled with oval cavities, like that of the others.
SEA-URCHINS AND SEA-CUCUMBERS. 287
The fourth kind of Pedicellaria, which I call P. stereo-
jJii/lla, is quite distinct from any of the others. It is
very minute, the head being only v^roth °f an inch in
height. The head is a kind of lengthened sphere, cut
into three segments, exactly as if an orange were divided
by three perpendicular incisions, meeting at the centre.
Thus the blades meet accurately in every part when
closed, but expand to a horizontal condition. These are
almost entirely calcareous, being invested but thinly with
the gelatinous flesh. They are filled with the usual oval
cavities, set in arched rows.
The head is set on a hollow gelatinous neck nearly as
Avide as itself, and thrown into numerous annular wrinkles ;
its walls are comparatively thin, disclosing a wide cavity,
apparently quite empty, as the blue calcareous stem ex-
tends only half-way from the base to the head. At this
point the neck contracts rather abruptly, and continues
to the base, but just wide enough to invest the stem.
This sort is confined, so far as I have seen, to the
ovarian plates and their vicinity, where they are nu-
merous.
Thus these tiny organs, so totally unlike anything with
which we may parallel them in other classes of animals,
do not merely afford us amusement, and delight us by their
elegance of shape and sparkling beauty, the variety and
singularity of their forms, the elaborateness of their struc-
ture, and the perfection of their mechanism, but excite
our marvel as to what can be the object which they sub-
serve in the economy of the creature, — what purpose can
be fulfilled by so many hundreds of organs, so singular
and scattered over the whole surface of the shelly body.
It is very difficult to answer this question. The only
organs with which they can be compared are the singular
" birds' heads " in so many of the Polyzoa, which we
looked at some time ago. But, unfortunately, a like mys-
tery enshrouds the use of those processes, and the only
288 EVENINGS AT THE MICROSCOPE.
light that we have as yet upon either form is that of dim
conjecture. It has been supposed that, in both cases, the
function of the prehensile forceps is to seize minute ani-
malcules or floating atoms of food, and pass them to the
mouth : but the supposition is involved in great difficul-
ties ; as the organs, however fitted for prehension, seem
peculiarly un suited for transmitting objects ; besides that
the great majority of them are placed very remote from the
mouth. I can only repeat the conjecture which I hazarded
in the case of the Polyzoan "bird's heads," viz., that the
pedicellarice are intended to seize minute animals, and to
hold them till they die and decompose, as baits to attract
clouds of Infusoria, which, multiplying in the vicinity of
the Urchin, may afford it an abundant supply of food.
There is yet another series of organs which stretch out
from every part of the surface of this living box; scarcely
less numerous than either the spines or pedicellarice, but
very different from both. They are what I alluded to just
now as the feet. Let us pay a moment's attention to their
appearance and action, before we examine their structure.
We see, then, extending from various points of the
shelly case of the Urchin, and reaching to twice or thrice
the length of the longest spines, slender pellucid tubes,
slightly tapering towards their free extremity, which then
abruptly dilates into a hemispherical knob, with a flat end.
These very delicate organs are extended or contracted at
the will of the animal, and turned in every direction,
waved hither and thither, and evidently have the faculty
of adhering very firmly by their dilated tips to any
object to which they are applied.
So much we can discern as we watch the creature dis-
porting in this vessel of water; but we will now endeavour
to learn a little more about its structure and economy.
Selecting for this purpose a sucker which is extended to
great length, I snip it across with a pair of sharp scissors,
as near the base as I can. Mark the result. The terminal
SEA-URCHINS AND SEA-CUCUMBERS.
289
SUCKER OF TJRCHIIT.
knob which was attached to the bottom of the saucer
maintains its hold, but the tube has suddenly shrunk up
to a sixth part of its
former length, ex-
changing at the same
time its smooth slen.
derness and translu-
cency for a wrinkled
semi-opacity. I push
the knob aside with a
needle's point and thus
destroy its adhesion ;
which done, I take
up the severed and
shrunken sucker, and lay it in a little sea-water in the
live-box.
Under a power of 180 diameters we see that the tube
is composed of two series of muscular fibres, the one set
running lengthwise, the other transversely or in rings ;
the former by their contraction diminishing the length of
the tube, the latter diminishing its calibre. The muscular
Avails are covered with a transparent skin, studded with
round orange-coloured spots, perhaps glandular, exactly
similar to those we saw on the exterior of the spines and
pedicellarice.
Now, to illustrate the action
of these tubular feet, I must
a^ain have recourse to the
denuded shell of a preserved
Echinus. Taking this globose
empty box in your hand, hold
it up against the light, looking
in at the large orifice, which
was once occupied by the
mouth : — you see that the
whole shell is pierced with
u
PORES OF URCHINS
290 EVENINGS AT THE MICROSCOPE.
rminute holes or pores, which are arranged in ten longi-
tudinal lines, associated so as to make five pairs of lines.
Now with a lens examine more minutely a portion of any
one of these lines, and you discern that it is composed
of a multitude of pores, which have a peculiar order of
arrangement among themselves; that is to say, they form
minor rows which cross, obliquely or diagonally, the
course of the longitudinal line. These rows are them-
selves double, the pores running in pairs, not however
with mathematical symmetry. In this species, there are
three pairs of pores in each row, and so there are in the
one which I have here alive, but in other of our native
species the rows consist of five pairs.
These pores are intimately connected with the tubular
feet, each of which springs from a portion of the shell
that is perforated with a pair of pores; so that the cavity
of every tube communicates with th3 interior of the
shelly box by two orifices.
Now, on the interior side of these two pores, — that is,
within the cavity of the shell, — there is placed a little
membranous, or rather muscular, bladder, filled with a
fluid which is not materially different from sea-water.
There is a free communication between the bladder within
^ind the tube without the shell, by means of the pair of
pores, through which the fluid passes. By means of the
muscular fibres, which are under the control of the
Urchin's will, any portion of this double vessel can be
contracted to a certain extent. Suppose it is the interior
bladder ; the effect of the contraction of its walls is to
diminish its capacity, and the contained fluid is forced
through the pores into the tube without. The longitudinal
fibres of this part being at the same moment relaxed, the
tube is lengthened, because of the injected water. Sup-
pose, now, in turn, the fibres of the tube contract, while
those of the bladder relax ; the fluid is driven back, the
bladder dilates, and the tube shortens, until, if the animal
SEA-URCHINS AND SEA-CUCUMBERS. 291
so please, its swollen tip is brought close up to the pores.
By mechanism so beautiful and simple is the prolongation
or abbreviation of these organs effected.
"We noticed, however, that the extremities of the tubes
had an adhesive power, which faculty it is that constitutes
them feet. They are prehensile ; and thus they afford, as
we observed in the living Urchin, the means by which it
takes hold of even a smooth and vertical surface, as the
side of a glass tank, and drags up its body thereby.
Putting, now, the extremity of this cut-off tube under
graduated pressure, having first applied to it a drop of
caustic potash, we see that it carries a beautiful glassy
plate of extreme thinness, which lies free in the swollen
cavity of the termination of the tube. This plate is cir-
cular in form, apparently notched at the margin, and cut
with four or five (for the number varies) incisions, which
reach almost to the centre. The substance is formed
of the common, clear, brittle, calcareous matter of the
skeleton, hollowed into numberless cavities, according to
the general plan. The centre is perforated with a larger
round orifice. The appearance of marginal notching is
deceptive; and indicates a structure analogous to what
we see in the spine. The notched line indicates the extent
-of the spongy structure ; but beyond this the plate extends
into a perfectly circular smooth edge, but is constituted
of a layer of calcareous substance so thin that there is
no room for the ordinary cavities within it.
The round aperture in the centre plays an important
part in the function of the organ. The foot adheres on
the same principle as that by which children take up large
flat stones with a piece of wetted leather, to the middle of
which a string is attached. The boy drops his sucker on
the stone, and treads firmly on it, to bring it into close
contact with the surface; then he pulls at the string per-
pendicularly, by which the central part of the leather is
lifted a little way from the stone, leaving a vacuum there ;
u 2
292 EVENINGS AT THE MICROSCOPE.
since the contact of the edges with the stone is so perfect
that no air can find entrance between them. Now the
pressure of the atmosphere upon
the leather is so great that a con-
siderable weight, perhaps half-a-
dozen pounds, may be lifted by
the string before the union yields*
Well, the very counterpart of
this amusing operation is repeated
by the clever "Urchin" whose
performances we are considering.
SUCKER-PLATE OF VRCHIX. ^^ ^^ ^ j^ ^^ . ^ tffofefi
end with the plate in it his leather ; his muscular power
acts like the other urchin's tread, to press the bottom of
the sucker against the surface of the rock. Then he pulls
the string ; in other words, he drags inwards the centre of
the muscular bottom of the sucker, which is, as it were,
sucked up into the central orifice of the plate. Thus a
vacuum is formed beneath the middle of the sucker, on
which the weight of the incumbent water and atmosphere
united presses with a force far more than sufficient to
resist the weight of his body, when he drags upon it, and,
as it were, warps himself up to the adhering point.
Here is in my cabinet a specimen of a Sea-Urchin of a
less regular form : it is the Heart-Urchin (Amjihidotus
cordatus). Essentially, its structure agrees with that of
the more globular forms ; but it is heart-shaped, and the
two orifices, instead of being at opposite poles, are sepa-
rated only by about one-third of the circumference. It
shows also singular impressed marks on its shell, as if
made by a seal on a plastic substance.
But what I chiefly wish to direct your attention to are
the spines. These differ much from the kindred organs
in Echinus, being far more numerous, very slender,
curved, thickening towards the tip, and lying down upon
the shell in the manner of hair, whence the species is
SEA-URCHINS AND SEA-CUCUMBERS. *293
sometimes called the Hairy Sea-egg. The array of spines
has a glittering silky appearance in this dried state.
We will now put a few of them under a low power of
the microscope, using reflected light and a dark back-
ground. They thus present a very beautiful appearance;
elegantly -formed curved clubs, made of a substance which
seems to be between glass and ivory, having the whiteness
of the latter and the glittering brilliance of the former.
The entire surface appears to be exquisitely carved, with
very minute oval pits, arranged in close-set lines, with the
most charming regularity. It is the light reflected from
the polished bottoms of these pits that imparts to the sur-
face its sparkling brilliancy. At the bottom of the spine
there is a little depression, which fits a tiny nipple on a
wart-like prominence of the shell, as we saw in Echinus;
but a little way above this point there is a singular pro-
jection or shoulder of the calcareous substance, which is
set-on at a very oblique angle with the axis of the spine,
reminding one, as we look at the spine laterally, of the
budding tines on the horn of a young deer.
At first, perhaps, you are at a loss to know what pur-
pose this shoulder can serve ; but, by turning to the shell,
and carefully observing the spines in their natural con-
nexion with it, you will observe that the obliquity of its
position accurately corresponds with the angle which the
individual spines form with the surface of the shell from
which they spring; and that the shoulder has its plane
exactly parallel with the latter, but raised a little way
above it. Now the entire shell, during life, was clothed
with a living flesh, having a thickness exactly correspond-
ing to the distance of the shoulder from the shell. This
shoulder, then, was an attachment for the muscular bands,
whose office it was to move the spine to and fro ; the pro-
jection affording the muscles a much better purchase, or
power, than they could have had if they had been inserted
into the slender stem itself.
294 EVENINGS AT THE MICROSCOPE.
The tubercles on the shell show a structure which cor-
responds with this. They are very minute; but each of
them is regularly formed, and is crowned with its little
polished nipple, on which, as I have said, the spine works,
as by a ball-and-socket joint. These are arranged with
perfect regularity in what is called quincunx* fashion; and
by close examination, you will see that each is inclosed in
a little area formed by a very low and narrow ridge of
the shell, which makes a network. On the lateral por-
tions of the under surface the meshes of this net are
particularly conspicuous ; and we see that they constitute
shallow hexagonal cells, in the midst of which are seated
the tubercles; yet not in the exact centre either, but
nearer the front than the back of the area inclosed.
Now this elevated ridge affords, doubtless, the insertion
of the other end of the muscles that move the spine ; the
ridge giving a better purchase than a flat surface, as the
keel on the breastbone of birds is deep in proportion to
the vigour of the muscles used for flight. And, surely,
the apparently trivial fact, that the space behind the
tubercle is greater than that in front, is not without
significance, since it implies a thicker muscle at that part,
which accords with the circumstance that such would be
the insertion of the muscle-band whose contraction pro-
duces the outward stroke by which the sand is forced
away from the bed.
But what is the need of so much care being bestowed
upon the separate motion of these thousands of hair-like
spines, that each individual one should have a special
structure with special muscles, for its individual move-
ment 3 The hairs of our head we cannot move individu-
ally : why should the Heart-Urchin move his 1 Truly,
these hairs are the feet with which he moves. The animal
inhabits the sand at the bottom of the sea in our shallow
bays, and burrows in it. By going carefully, with the lens
* See page 60 for an explanation of this term.
SEA-UBCHINS AND SEA-CUCUMBERS. 295'
at your eye, over the shell, you perceive that the spines,
though all formed on a common model, differ considerably
in the detail of their form. I have shown you what may
be considered the average shape; but in some, especially
the finer ones that clothe the sides, the club is slender and
pointed ; in others, as in those behind the mouth, which
are the largest and coarsest of all, the club is dilated
into a long flat spoon ; while in the long, much-bowed
spines which densely crowd upon the back, the form is
almost uniformly taper throughout, and pointed.
The animal sinks into the sand mouth-downwarcls. The
broad spoons behind the mouth come first into requisi-
tion, and scoop away the sand, each acting individually,
and throwing it outwards. Observe how beautifully they
are arranged for this purpose ; diverging from the central
line, with the curve backwards and outwards. Similar
is the arrangement of the slender side-spines ; their curve
is still more backwards, the tips arching uniformly
outwards. They take, indeed, exactly the curve which
the fore-paws of a mole possess (only in a retrograde
direction, since the Urchin sinks backwards), which has
been shown to be so effective for the excavating of the
soil, and the throwing of it outwards. Finally, the long
spines on the back are suited to reach the sand on each
side, when the creature has descended to its depth, and
by their motions work it inward again, covering and
concealing the industrious and effective miner.
Thus we have another instance added to the ten thou-
sand times ten thousand, of the wondrous wisdom of God
displayed in the least and most obscure things. "All
Thy works shall praise Thee, 0 Lord ! " (Ps. cxlv. 10).
There is an order of animals which naturalists put in
the same category as the Sea-Urchins, but which an un-
scientific observer would regard as possessing little or no
affinity with them. Some are like long, soft, and fleshy
worms, and others, which come the nearest to the crea-
296 EVENINGS AT THE MICROSCOPE.
tures we have been looking at, have still the lengthened
form, which, however, so closely resembles that of a warty
angled cucumber that the animals I allude to are familiarly
called Sea-cucumbers (Holothuriadce). The marine zoo-
logist frequently finds them beneath stones at extreme low
water ; and larger forms, as big in every direction as a
marketable cucumber, are occasionally scraped from the
bottom of the deep sea by means of that useful instrument,
the dredge. If you drop one of them into sea-water, you
will presently see from one extremity an exquisite array
unfold, like a beautifully cut flower of many petals, or,
rather, a star of ramifying plumes. Soon it begins to
climb the walls of your aquarium, and then you catch the
first glimpse of its affinity to the Urchins ; for the short
warts which run in longitudinal lines down the body
corresponding to the angles, gradually lengthen them-
selves, and are soon perceived to be sucking-feet, analogous
in structure and in function to those with which the
Star-fish and the Sea-Urchin creep along.
But the relationship becomes more apparent still when
we find that the Cucumber has a skeleton of calcareous
substance deposited on exactly the same plan as in the
Urchin, viz., around insulated rounded cavities. It is true
you may cut open the animal and find nothing at all more
solid than the somewhat tough and leathery skin ; but a
calcareous skeleton is there notwithstanding, though in
truth only a rudimentary one. If we were to cut off a
considerable fragment of the skin, and spread it out to dry
upon a plate of glass, and then cover it with Canada
balsam, we should find (assisted by the translucency
which is communicated to the tissues by the balsam) that
the skin is filled with scattered atoms of the calcareous
structure, perfectly agreeing with that with which the
solid framework of the Urchin is built up ; but minute
and isolated in the flesh, instead of being united into
one or more masses of definite organic form.
SEA-URCHINS AXD SEA-CUCUMBERS. 297
But the atoms I speak of are still more perfectly seen
by dissolving the piece of skin in boiling potash, and
-washing the sediment twice or thrice in pure water ; this
may then be spread upon a glass slide, and covered with
a plate of thin glass, when it forms an interesting and
permanent object for study. I have here a slide which
is the result of such treatment; to the naked eye it
appears sprinkled with the finest dust, but under mag-
nifying power it is seen to consist of numberless cal-
careous bodies, of great beauty, and very free from
extraneous matter.
The elegance of the forms is remarkable, and also
their uniformity ; for though there do occur here and
there among them plates of no regular shape, perforated
with large or small roundish orifices, yet the over-
whelming majority are of one form, subject to slight
modifications in shape and size.
Neglecting, then, the irregular pieces, we perceive that
the normal form is an oval of open work, built up by the
repetition of a single element. That element is a piece of
clear glassy material, highly refractive, of the shape of a
dumb-bell : two globes united by a thick, short column.
The oval is constructed thus : — suppose two dumb-bells to
be placed in contact, side by side, and soldered together,
there would be of course an oval aperture between their
-columns. Then two other dumb-bells are united to these
in a similar manner, but one on each side, so that the
globes of each shall rest in the valley between the former
globes now united. These then are soldered fast in like
manner ; and the result is that there are three oval aper-
tures. The next step is that on the top of the four united
globes two other dumb-bells stand erect, and lean over
towards each other till their upper globes come into con-
tact, their lower ones remaining remote; these are soldered
to the mass and to each other at the points of contact,
.leaving a fourth aperture. The same is repeated at the
298
EVENINGS AT THE MICROSCOPE.
DUMB-BELLS IX HOLOTEVHIA.
opposite end by two other dumb-bells ; and the structure
is complete as you see it. In almost all cases the two
united globes of these ter-
minal elements are fused
into one globe, and in not
a few instances the ap-
pearance is as if these
two dumb-bells were but
one, bent over in a semi-
circular form ; but still a
good many specimens oc-
cur in which the two dumb-bells can be quite distinguished
from each other. The calcareous matter that solders the
elements together seems abundant, and has the appear-
ance that would be presented if they had been made of
solid glass, and united by glass in a state of fusion ; the
latter having apparently run together, so as to smooth
and round angles and fill up chinks, even where, as is
often the case, the globes themselves have only mutually
approximated, and not come into actual contact.
The average dimensions of these oval aggregations
may be .004 inch in length, and a little more than .002
in width ; but some specimens occur which are a little
larger, and others a little smaller than this ; while the
irregular plates are sometimes three times the length.
Some of the more worm-like
members of this class have,
however, a skeleton composed
of pieces imbedded in their
skin, of even more remark-
able shapes than these. One
of these is the CJdrodota
violacea ; a native of the
southern coasts of Europe.
We have indeed a British
species of the same genus, a
^**^~~f^
WlIKhL UN IH1KODOTA.
SEA-URCHINS AND SEA-CUCUMBERS. 299
specimen of which is in my possession, but I have vainly
examined the skin for any structure analogous to this.*
In the Mediterranean species the skin, especially of the
belly-side, is described as filled with plates exactly re-
sembling broad and thin wheels of glass, supported by
four, five, or six radiating spokes, and having the inner
edge of the hoop cut into teeth of exceeding delicacy.
Another animal remarkable for the furniture of its skin
is the genus Synapta, which is very similar in form, and
closely allied, to the Chirodota. It is very common in the
Adriatic and Mediterranean seas, but has not yet been
taken on the British coasts. I would counsel you, how-
ever, to have your eyes open if you have the opportunity
of searching our coasts ; for, as M tiller found one species,
the Synapta inhcerens, on the shores of Denmark, it is not
at all unlikely that we may possess either it or some other.
Should it ever come into your hands, slit open the skin of
the belly, where you will find, imbedded in little papilla-
or warts, some highly curious spicula
or calcareous forms. Each consists
of an oblong plate, perforated with
large holes in a regular manner, and
having a projection on its surface near
one extremity, to which is jointed a
second piece, having the most singu-
larly true resemblance to an anchor. The flukes of this
anchor project from the skin, the shank standing obliquely
upward from the plate, to which it is articulated, where
the ring would be, by a dilatation which is cut into
teeth, f
* The most careful and repeated search has not availed me to find
in the skin the least trace of calcareous atoms ; but this may possibly
be because I had unfortunately preserved my specimen in acetate of
alumina, and the acetic acid has perhaps dissolved the lime.
*T Since the printing of the above, an admirable paper has appeared
in the proceedings of the Zoological Society of London, by Messrs.
Woodward and Barrett, " On the Genus Synapta." These authors in-
AXCHOB-PLATE I2T STXAFTA.
.300 EVENINGS AT THE MICROSCOPE.
Among the multitude of transparent creatures that swim
in the open sea, few are more interesting than the infant
state of the very animals that we have lately been examin-
ing ; the Sea-Urchins and their allies. It is a productive
way of obtaining subjects for microscopic research, to go
out in a boat on a quiet summer's day, especially in the
afternoon, when the sun has been shining, or when even-
ing is waning into night, and, with a fine muslin net
stretched over a brass ring at the end of a pole, skim the
surface of the smooth sea. At intervals you take in your
net, and having a wide-mouthed glass jar ready, nearly
filled with sea-water, invert the muslin in it, when your
captures, small and great, float off in the receiver. After
a few such essays, unless you have very bad success in-
deed, you will see even with the naked eye, but much
more with a lens, that the water in your jar is teeming
form us that two species of Synapta are found in the British seas, one
of which, the Chirodota digitata of E. Forbes, is the species referred
to in the text as being in my own possession. Its skin proves to be
studded with anchors, not with wheels, and it is on this ground re-
ferred to the genus Synapta.
Still later (See Qu. Jourti. Micr. Scl. for 1862, p. 131), Dr. Wyville
Thompson has obtained Synapta inhazrens in the Irish Loughs of Belfast
and Strangford. In his admirable paper, elaborately illustrated, on the
infancy and development of this curious creature, he has traced the
gradual formation of the calcareous spicula, from their first indication.
The anchor first appears as a straight rod sharp at both ends. One end
gradually becomes knobbed ; the knob extends on each side, giving the
rod a T form ; and soon the arms curve backward, giving the anchor-
form. Then the basal end becomes dilated. Hitherto no trace of the
plate has appeared ; but now a small glassy needle is seen lying across
the shank near the base. Each extremity of this now branches, and
these again branch, the points meeting and uniting here and there,
until at length the plate is gradually mapped out. As yet the openings
left by the uniting network are smooth-edged ; but the glassy network
gradually strengthens, and the edges of the holes, now uo longer
meshes of a net, but orifices in a plate, are studded wit i teeth all
ound. I refer my readers, for much information of he deepest
interest, to this very valuable memoir.
SEA-URCHINS AND SEA-CUCUMBERS. 301
with microscopic life ; and though many of your captives
will not long survive the loss of their freedom, still
meanwhile you may secure many an interesting object,
and examine it while yet the beauty and freshness of
life remain. And, moreover, with care and prudence,
some selected subjects may be maintained in vigour, at
least long enough to afford you valuable information on
the habits, economy, metamorphosis, and development
of animals, of which even the scientific world knows as
yet next to nothing.
I have just been so fortunate as to obtain in this way
one of our Sea- Urchins in its larva state ; and have it
now in the thin glass trough which is on the stage of the
microscope. It is just visible to the unassisted sight as a
slowly moving point in the clear water, when the vessel
is held up to the light ; but with the low power which I
am now using, it is distinctly made out in all its parts,
and is an object of singular elegance and beauty.
It is, as you see, somewhat of the figure of a helmet,
the crest rising to a perpendicular point, which is
rounded, the vizor or mask descending far down, and
ending in two points, and a long ear hanging down on
each side, so as to reach the shoulders of the wearer.
Of course such comparisons are fanciful, but they assist
one in intelligible description.
Now, the entire helmet is composed of a gelatinous
flesh of the most perfect transparency, so that we can
see with absolute clearness everything that is within it
And the first thing that strikes us is, that a framework
or skeleton of extreme delicacy, composed of glassy rods,
supports the whole structure. Look carefully at this, and
mark its symmetry and elegance. There is, then, first, a
rod which passes through the crest perpendicularly, and
carries at its lower extremity a horizontal ring. To the
opposite sides of this ring are soldered two other very
slender rods, passing down nearly in a perpendicular
302 EVENINGS AT THE MICROSCOPE.
■direction, but a little diverging ; and two other shorter
rods pass down from the front of the ring, parallel to these.
After a while each lateral pair of rods is united by a short
cross-piece, and the result is four lengthened rods, two of
which go down through the vizor into the chin-points,
and two larger and stouter ones through the ears into
the shoulder- points. This, then, is the solid skeleton,
the interest of which is much enhanced, when we observe
that it is formed, on the common plan, out of perforated
lime-glass, the two ear-rods and the crest-rod being
pierced with a regular series of oval holes, and bearing
on their edges corresponding projecting points.
Now, to turn again to the gelatinous flesh. The inner
surface of the vizor, or that which would be in contact
with the face of the wearer, supposing it to be a real
helmet, has a great squarish orifice with a thickened
margin, which we see by its movements to be highly sen-
sitive and contractile. This square orifice is the mouth
of the larva, and it leads into a cavity in the upper part
of the vizor, which is the gullet ; and this in its turn ter-
minates in a narrowed extremity, which passes into the
orifice of a greater and higher cavity, the lip of which
embraces it just as the bunghole of a barrel receives and
embraces the tube of a funnel. The latter cavity occu-
pies the chief part of the volume of the helmet, the four
rods diverging to inclose it. It is the stomach.
It adds to the beauty of the little helmet-shaped crea-
ture that, while the greater portion of the substance is
of the most colourless transparency, the summit of the
crest and the tips of the shoulder-points are tinged with
a lovely rose red. The whole exterior surface is, more-
over, studded with those minute and glandular specks,
with which every part of the adult Urchin is covered ;
and the light is reflected from the various prominences
with sparkling brilliancy.
The little creature moves through the water with much
SEA URCHINS AND SEA-CUCUMBEKS.
303
grace and with a dignified deliberation ; the crest being
always uppermost, and the perpendicular position invari-
ably maintained. It does not appear capable of resting,
its movements depending on incessantly vibrating cilia.
These organs we perceive densely cloth-
ing the long ear-pieces, but more espe-
cially accumulated and more vigorous,
in a thickened, fleshy band, which
passes partly round the whole helmet,
at the origin of these pieces.
You do not discern the slightest re-
semblance of form between this little
slowly-swimming dome and the spined
and boxed Urchin which crawls over
the rocks ; and you wonder by what
steps the tiny atom of one-fortieth of an
inch in length is led to its adult stage.
Fortunately I can satisfy your curiosity
on this point, not indeed from my own
observations, but from those of Professor
Johann Miiller, whose discoveries of
the developments of these and kindred
animals are among the most interesting, because the most
startling, of the marvels which modern zoology has re-
vealed to us. The whole process is full of surprising
details, to which the change of the caterpillar to a chrysalis,
and the chrysalis to a butterfly, presents no parallel, won-
derful as those changes of form appear and are. There we
have but modifications of outward form, produced by the
successive moults or castings of the external skin, and the
gradual growth of the animal, which has from the first
been present, though veiled. But the construction of the
Sea-Urchin is by no means a process of skin-casting, nor
has it any recognised parallel in the whole economy of
natural history. It is a development perfectly unique. I
will endeavour to make you acquainted with the results
LAEVA OF SEA-TTBCHIN'.
304 EVENINGS AT THE MICROSCOPE.
arrived at from the researches of the eminent German
zoologist, to whom we are indebted for almost all we
know on the matter.
Let me first premise that this beautiful helmet-shaped
creature is not the future Urchin; and, strange to say,
that only a very small portion of the present structure,,
namely, the stomach and gullet, will enter into its com-
position. The helmet is a kind of temporary nurse,
within which the future Urchin is to be formed, and by
which it is to be carried from place to place by its ciliary
action, while the young animal is gradually acquiring the
power of independent life ; when the whole constitution
of the nurse will waste away and vanish !
The first trace of the young Urchin is a filmy circular
plate, which is not symmetrical with the helmet, nor
formed even on the same plane, but appears obliquely
fixed on the interior of the stomach, on one side, close to
the arch of transparent flesh which stretches from one
of the points of the vizor to one of the ear-points. Herr
Miiller compares the larva (which is not helmet-shaped in
every species) to a clock-case, of which the vizor, with its
hanging gullet and mouth, forms the pendulum; and then
the newly-formed disk represents the face of the clock ;
only that it is put on the side instead of the front. Now
this tiny disk gradually grows into the form and assumes
all the organs of the Urchin, while the enveloping nurse,
flesh, rods, and all, wastes away to nothing.
The disk, soon after its appearance, is seen to bear pro-
minences on its surface, in which is traced the figure of a
cinque-foil, the elements being five warts set symmetri-
cally. These lengthen and grow into suckers, essentially
identical with those of the adult, but most dispropor-
tionately large. In the five triangular interspaces between
these, little points and needles of solid calcareous glass
begin to form, very much like the crystals that shoot
across a drying drop of a solution of some salt; these catch
EA-URCHINS AND SEA-CUCUMBERS.
305
and unite, first into "|~-, and then into (-{-forms, and then
into irregular networks. Meanwhile, fleshy cylindrical
columns spring up from the surface, one in each of these
interspaces, and presently develop within their substance
a similar framework of porous glass; these soon are seen
to be the spines, and each is seated on a little nucleus of
network, on which it possesses the power of rotating.
At the same time pedicellariae begin to be formed; and,
what is specially marvellous, they are first seen, not on
the disk, which alone is to be the future Urchin, but on
the interior wall of the helmet, which is even now in pro-
cess of being dissipated, and even on the opposite side to
that which carries the disk. They commonly appear four
in number, arranged in two pairs ; and we can see in them
— they being, like the suckers, large out of all proportion
to the disk — the stem, and the three-leaved heads, which
already exercise their characteristic snapping movements.
The disk is meanwhile enlarging its area ; and the
spines and suckers, gradually lengthening, at length push
themselves through the walls of the helmet; the hanging
points and crest of which are
fast diminishing by a kind of
insensible absorption ; the ci-
liary movements become less
vigorous,and the mouth closes
up. But, correspondently, the
Urchin isbeginning to acquire
its own independent power of
locomotion; for the suckers,
now ever sprawling about, are
capable of adhering to any
foreign body with which they
come into contact, and of dragging the whole structure
about, by their proper contractions. The cilia that cover
the thickened fringing band still exercise their powers,
and are the last to disappear.
x
YOU>*G SEA-VRCHIN:
DEVELOPMENT OF DISK.
30G EVENINGS AT THE MICROSCOPE.
When the disk has grown to such an extent as to spread
over about half of the larval stomach, very little remains
of the helmet, except the middle portions of the glassy
rods and the ciliary bands; all the rest of this exquisitely
modelled framework having vanished by insensible
degrees, no one knows how or where. The stomach and
gullet, indeed, are gradually sucked into the ever-growing
disk ! But all the rest, flesh and rods, fringes, bands,
and cilia, waste away to nothing.
The mouth of the larva has no connexion with the
mouth of the Urchin. The little isolated patches of glassy
network continue to spread through the flesh of the disk,
until the whole forms one uniform structure, and con-
stitutes a series of plates. The mouth is that spot in the
centre, over which the calcareous frame is last extended ;
and it is first distinguishable by the appearance of five
glassy points, which soon develop themselves into the five
converging jaws, which we see forming such a curious
apparatus on the inferior side of the Sea-Urchin.
Actual observation has not traced the infant animal
beyond this stage of the development ; but Professor
Miiller has taken specimens, swimming in the sea, in
which scarcely a rudiment of the larva remained. They
had the form of round flattened disks, which freely moved
their spines, and crawled about the sides of the vessel in
which they were kept by means of their suckers, exactly
in the manner of the adult Urchin.
"Thus ends this strange, eventful history;" and in
reviewing it, one can scarcely avoid being impressed with
a sense of the majesty of God in these His humbler works.
By what wonderful, what unexpected roads does He arrive
at the completion of His designs ! And if such things as
these are only now bursting upon our knowledge, after
thousands of years of man's familiar contact with the
inferior creatures, how many more wonders may yet
remain to be unfolded, as science pursues her inves-
tigations into the Divine handiwork !
JELLY-FISHES. 307
CHAPTER XVII.
JELLY FISHES.
As this afternoon was delightfully calm and warm, the
very model of an autumnal day, I took my muslin ring-
net and walked down to the rocks at the margin of the
quiet sea. Nor was I disappointed ; for the still water,
scarcely disturbed by an undulation, and clear as crystal,
was alive with those brilliant little globes of animated jelly,
the Ciliograde and Naked-eyed Medusae, apparently little
more substantial than the clear water itself. Multitudes
of them were floating on the surface, and others were
discerned by the practised eye, at various depths, shoot-
ing hither and thither, now ascending, now descending,
now hanging lightly on their oars, and now, as if to
make up for sloth, darting along obliquely with quickly-
repeated vigorous strokes, or rolling and revolving along,
in the very wantonness of humble happiness.
After gazing awhile with admiration at the undisturbed
jollity of the hosts, I made a dip with my net, the interior
of which, on lifting it from the water, was lined with
sparkling balls of translucent jelly. They were far too
numerous to allow me to transfer them all to captivity ;
they would soon have choked up and destroyed one
another ; I therefore selected the finest and most interest-
ing, shaking an example or two of each kind into my
glass jar of sea-water, where they immediately began to
frolic and revel as if still in the enjoyment of unrestricted
liberty. And here they are.
Among these bright and agile beings which are shooting
x 2
308 EVENINGS AT THE MICROSCOPE.
their wayward traverses across each other, and intertwin-
ing their long thread-like tentacles, we will select one or
two for examination, as samples of their kindred. And
first let me separate this active little Beroe (Cydipjjepomi-
formis), which I dip out with a tea-spoon and transfer to
this other glass jar, that we may watch its form and
movements unaffected by the presence of its companions.
We see, then, a little ball, almost perfectly globular,
except that a tiny wart marks one pole, of the size of a
small marble, and apparently turned out of pure glass, or
ice, or jelly — according to your fancy, — perfect transpa-
rency and colourlessness being its characteristics ; so much
that it is not always easy to catch sight of the little crea-
ture, except when we allow the light to fall on the jar in a
particular direction. From two opposite sides of the globe
proceed two threads of great length and extreme tenuity,
which display the most lively and varied movements.
These filaments shall occupy us for a few moments.
We trace them to their origin, and find that they proceed
each from the interior of a lengthened chamber, on each
of two opposite sides of the animal. Suddenly, on the
slightest touch of some foreign object, one of the threads
is contracted to a point and concealed within its chamber,
but is presently darted forth again. When the lovely
globe chooses to remain still, the threads hang downward,
gradually lengthening more and more, till their ex-
tremities lie along the bottom of the jar extended to a
length of six inches from the chamber. Then we see
that this delicate thread is not simple, but is furnished
along one side, throughout its length, at regular distances,
with a row of secondary filaments, which project at right
angles from the main thread.
These secondary filaments constitute an important ele-
ment in the charm which invests this brilliant little crea-
ture. They are about fifty in number on each thread, and
some of them are half an inch long, when fully extended,
JELLY-FISHES. 309
but it is seldom that we see them thus straightened; for
they are ever assuming the most elegant spiral coils, which
open and close, extend and contract, with an ever chang-
ing vivacity. The animal has a very perfect control over
each thread, as well as over each individual secondary
filament. They are, either together or separately, fre-
quently projected from their chambers to their full extent,
by one impulse; sometimes the extension is arrested at
any stage, and then proceeded with, or the thread is par
tially or entirely retracted. Sometimes the secondary fila-
ments are coiled up into minute balls, scarcely percep-
tible, or only so as to give to the thread the appearance of
small beads remotely strung on a fine hair; then a few
uncoil and spread divergently ; contract again, and again
unfold; or many, or all, interchange these actions toge-
ther, with beautiful regularity and uniformity, repeating
the alternation for many times in rapid succession.
The beauty and diversity of the forms assumed by these
elegant organs beguile us to watch them with unwearied
interest, and we wonder what is their function. For, with
all our watching, this is by no means clear. They are
certainly not organs of motion. At times it seems as if
they were cables intended to moor the animal, while it
floats at a given depth; for we see them with their ex-
tremities spread upon the bottom, to which they appear
to have a power of adhering, thus forming fixed points,
from which the little globe rises and falls at pleasure,
shortening or lengthening its delicate and novel cables,
maintaining all the while its erect position.
When the Cydippe swims, however, which it does with
great energy, the threads seem unemployed, streaming
loosely behind, and evidently taking no part in the pro-
gression, though still adding beauty and grace to the tout
ensemble. The organs by which the sprightly motions
of the whole animal are effected are of quite another
character, and shall now engage our attention.
'310
EVENINGS AT THE MICROSCOPE.
. You have doubtless observed, while gazing on the
animal, a peculiar glittering appearance along its sides,
mingled in certain lights with brilliant rainbow-reflections.
Now let us take an opportunity, when it approaches the
side of the glass, to examine this appearance with a lens.
The globe, you see, is marked by longitudinal bands, eight
in number, set at equal distances, and ranging like meri-
dians, except that they do not quite reach to either pole.
These bands are the seats of the motile organs, which
are highly curious, and in some sort peculiar.
Each band is of considerable width in the middle, but
becomes narrower towards the extremities. It carries a
CYDIPPE.
number — usually from twenty to thirty — of flat thin
membranous fins, set at regular distances, one above the
other, which may be considered as single horizontal rows
of cilia, agglutinated together into flat plates. Each plate
has a rapid movement up and down, from the line of its
insertion into the band, as from a hinge, and thus strik-
ing the water downwards, like a paddle. The whole
band may be likened to the paddle-wheel of a steamer,
except that the paddles are set in a fixed line of curvature
JELLY-FISHES. 311
instead of a revolving circle. The effect, however, is
exactly the same : that of paddling the beautiful little
globe vigorously through the water. The prismatic colours
are produced by the play of light on their glittering
surfaces, which are ever presented to the eye of the
beholder at changing angles.
We rarely see these rows of paddle-fins wholly at rest,
but occasionally one or two bands will be alone in a state
of vibration ; or one or more will suspend their action
while the rest are paddling. Sometimes, in a band that
is at rest, a minute and momentary wave will be seen to
run rapidly along its length. All these circumstances
show that the ciliary motion is perfectly under the con-
trol of the animal's will, not only in the aggregate, but
in every part.
In an excellent memoir on this animal by Mr. It.
Patterson, of Belfast,* there are some interesting obser-
vations on the power of its tissues to become tinged with
extraneous colours, a fact which may be useful to you
in your researches, as enabling you with more ease and
precision to demonstrate the internal structure.
" From the inconsiderable quantity of solid material
(remarks this observer) " which enters into the body of
the Beroes, and the rapid circulation of water, which is
apparent throughout their frame, we would naturally
suppose that any tinge which the body might accidentally
acquire would be extremely fugitive. It was found, how-
ever, to be much less so than a priori would have been
expected. My attention was drawn to this peculiarity by
the circumstance of all my glass vessels being one evening
occupied by Beroes and Crustacea, so as to compel me to
place a small Medusa in a tin vessel, which chanced to
be rusted at the seams. Next morning the colourless
appearance of the animal was changed into a bright
yellow, which appeared to pervade every part, and doubt-
* "Trans. Roy. Irish Academy," vol. xix. pt. 1.
312 EVENINGS AT THE MICROSCOPE
less arose from the oxide of iron, diffused through the
sea-water. This tint remained during the entire day,
although the animal was transferred to pure sea-water.
Wishing to try if the vessels of the Beroe would become
distinct, if filled with some coloured fluid from which the
animal could suddenly be withdrawn, and viewed through
the usual transparent medium of sea-water, I placed a
Beroe in a weak infusion of saffron. At the end of
twenty minutes its colour had undergone a perceptible
change. I allowed it, however, to remain immersed for
about six or seven hours, when it had assumed a bright
yellow hue. It was then placed in pure sea-water, but
retained its yellow colour for twenty-four hours after-
wards; and though it gradually became fainter, it was very
perceptible even at the expiration of forty-eight hours."
I am sure you will pardon my interrupting your micro-
scopic gazings for a moment by quoting the following
charming lines bv the Rev. Dr. Drummond, which were
elicited by his having watched with pleasure the elegant
form and motions of this little creature : —
" Now o'er the stern the fine-meshed net-bag fling,
And from the deep the little Beroe bring :
Beneath the sun-lit wave she swims concealed
By her own brightness ; — only now revealed
To sage's eye, that gazes with delight
On things invisible to vulgar sight.
When first extracted from her native brino,
Behold a small round mass of gelatine,
Or frozen dew-drop, void of life or limb :
But round the crystal goblet let her swim
'Midst her own element— and lo ! a sphere
Banded from pole to pole— a diamond clear,
Shaped as bard's fancy shapes the small balloon
To bear some sylph or fay beyoud the moon.
From all her bands see lucid fringes play,
That glance and sparkle in the solar ray
With iridescent hues. Now round and round
She wheels and twirls — now mounts — then sinks profound-
Now see her, like the belted star of Jove,
Spin on her axis smooth — as if she strove
JELLY-FISHES. 313
To win applause — a thing of conscious sense,
Quivering and thrilling with delight intense.
Long silvery cords she treasures in her sides,
By which, uncoiled at times, she moors and rides ;
From these, as hook-hairs on a fisher's line,
See feathery fibrils hang, in graceful twiue,
Gracef ul as tendrils of the mantling vine ;
These, swift as angler by the fishy lake
Projects his fly, the keen-eyed trout to take,
She shoots with rapid jerk to seize her food,
The small green creatures of crustaceous brood :
Soon doomed herself a ruthless foe to find,
When in th' Actinia's arms she lies entwin'd.
Here prison'd by the vase's crystal bound,
Impassable as Styx's nine-fold round,
Quick she projects, as quick retracts again,
Her flexile toils, and tries her arts in vain ;
Till languid grown, her fine machinery worn
By rapid friction, and her fringes torn,
Her full round orb wanes lank, and swift decay
Pervades her frame till all dissolves away.
So wanes the dew, conglobed on rose's bud ;
So melts the ice-drop in the tepid flood :
Thus, too, shall many a shining orb on high
That studs the broad pavilion of the sky,
Suns and their systems, fade, dissolve, and die."
While we have been admiring our lovely little Cydippe,
and comparing notes with other observers and admirers ;.
other species as small, as transparent, as sprightly, and
scarcely less elegant, have been impatiently waiting for
their share of admiration ; shooting to and fro, tossing
about their little bells of ductile glass, and alternately
lengthening and snatching-in their sensitive tentacles, in
astonishment at our stoical indifference to their charms,
and saying, after their manner, with the little urchin
whose feelings were hurt by the neglect of his papa's
visitor, — " You don't notice how beautiful I be !"
A thousand pardons, sweet little Sarsia! We will now
give you our undivided attention ; and for this end we
must take the liberty of catching you, and of transferring
your translucency to solitary grandeur in this other glass.
314 EVENINGS AT THE MICROSCOPE.
Ha ! but you don't want to be caught, eh 1 And so you
pump and shoot round and round the jar as the spoon
approaches ! Truly you are a supple little subject, difficult
to catch as a flea, and difficult to hold (in a spoon) as an
eel. But here you are at last, lying as motionless and as
helpless in the silver as a half-melted atom of calf's-foot
jelly, to which, indeed, you possess no small resemblance.
Look at the pretty little Medusa in his new abode, at
once recovering all his jelly-hood as he feels the water
laving him, and dashing about his new domain with a
vigour which makes up for lost time.
It is a tall bell of glass a little contracted at the mouth
— its outline forming an ellipse, from which about a third
has been cut off. The margin of this bell carries four tiny
knobs, set at equal distances, and thus quartering the
periphery ; and these are the more conspicuous, because
each one is marked with a bright orange-coloured speck.
Physiologists are pretty well agreed to consider such
specks as these, on the margins of the smaller Medusce,
as eyes, — rudimentary organs of vision, capable, probably,
of appreciating the presence and the stimulus of light,
without the power of forming any visual image of ex-
ternal objects. You will not gain much information
about their function from microscopic examination ; for
all you can discern is an aggregation of coloured specks
(pigment-granules) in the midst of the common jelly.
The knobs, however, are connected with other organs ;
for from each of them depends a highly sensitive and very
contractile tentacle. Sometimes one, or more, or all, of
these organs hang down in the water motionless, lengthen-
ing more and more, especially when the bell is still, until
they reach a length some twelve or fifteen times that of
the bell, or umbrella. Then suddenly one will be con-
tracted, and, as it were, shrivelled, to a mere fragment a
quarter of an inch long ; then lengthened again to an
inch or two; then shortened again. Now the little bell
JELLY-FISHES. 315
resumes its energetic pumping, and shoots round and
round in an oblique direction, the summit always going
foremost, and the tentacles streaming behind in long trail-
ins lines. Now it is acrain arrested : the bell turns over
on one side and remains motionless, and the tentacles,
"fine as silkworm's threads," float loosely in the water,
become mutually intertangled, instantly free themselves
pucker and shrivel up, slowly lengthen, and hang motion-
less again, or, as the bell allows itself to sink slowly, are
thrown into the most elegant curves and arches.
Though these tentacles look at first like simple threads
of extreme tenuity, yet when viewed closely they are seen
to be composed of a succession of minute knobs separated
by intervals, like white beads strung on a thread ; the
beads being more remote from each other in proportion
as the tentacle is lengthened.
This structure is worthy of a more minute investigation.
We will therefore confine our little Sarsia in this narrow
glass trough, which is sufficiently deep to allow its whole
form to be immersed, though somewhat flattened; which
is an advantage, as its movements are thereby impeded.
Now, with a power of 300 diameters, you see that each of
the knobs of the tentacle is a thickening or swelling of the
common gelatinous flesh, in which are imbedded a score
or two of tiny oval vesicles, or bladders, without any very
obvious arrangement; but for the most part so placed that
the more pointed end of each is directed towards the cir-
cumference of the thickening. The intermediate slender
portions of the tentacle — the thread on which the beads
are strung — is quite destitute of these vesicles.
These little bodies are called cnidce; and, in the whole of
this class of animals, and also in that of Zoophytes, they
play an important part in the economy of the creature. I
shall probably take occasion to exhibit them to you under
conditions more favourable than are presented here, viz.,
in the Sea- Anemones, where they attain far greater dimen-
316
EVENINGS AT THE MICROSCOPE.
sions; and therefore I will merely say here that each one
of these tiny vesicles carries a barbed and poisoned arrow,
which can be shot forth at the pleasure of the animal with
great force, and to an amazing length; that hundreds are
usually shot together; and that this is the provision which
the All-wise God has given to
these apparently helpless animals
for securing and subduing their
prey.
There is, however, another
organ still more conspicuous in
our little Sarsia, of which I have
not yet spoken. As the whole
animal has the most absolute
i transparency, we see that the
\ roof of the bell is much thicker
I than the sides, and that it graclu-
j ally thins off to the edge. The
i' interior surface is called the sub-
i t
S \ umbrella, and it carries within
/ I its substance four slender tubes,
/ j which, radiating from the centre
i of the roof, proceed to the mar-
• gin, where they communicate
with another similar canal which
runs round the circumference,
/
sending off branches into the
tentacles. This is the circulatory
sabsia. system; and you may see, with
the magnifying power which you
are at present using, that a clear fluid is moving rapidly
within all these canals, carrying minute granules; not
with an even forward current, but with an irregular
jerking movement, as if several conflicting eddies were
in the stream. Yet we discern that, on the whole, the
granules are moved forward; passing from the centre of
JELLY-FISHES. 317
radiation towards the margin, when we see them slip
into the marginal canal from the several openings of the
radiating canals.
This is a very simple and rudimentary blood-system.
There is here no heart with its pulsations, no proper
arteries or veins, no lungs for oxygenation; but the pro-
ducts of digestion are themselves thus circulated through
the system. And this brings me back to the central point,
whence you see depending the curious organ I spoke of.
A long cylinder of highly movable and evidently sensitive
flesh hangs down from the middle of the roof exactly like
the clapper of a bell ; and, as if to add to the resem-
blance, this same clapper is suspended by a narrow cord,
and is terminated by a knob.
Sometimes this whole organ is allowed to hang about
as low as the edge of the bell; then it gradually lengthens
to twice, thrice, nay, to five times that length ; the tongue
lolling out of the mouth to a most uncouth distance, and
even the suspending cord (as I presume to term the at-
tenuated basal portion) reaching far beyond the margin ;
then, on a sudden, like the tentacles, the tongue is con-
tracted, thrown into wrinkles, curled into curves, and
the whole is sheltered within the concavity ; presently,
however, to loll out again.
This proboscis-like organ is called the peduncle, and its
office is that of a stomach, of which the knob at the end
is the mouth, having a terminal orifice with four minute
lips. The flexible substance and rapid motions of this
peduncle are suited to enable it to seize small passing
animals that constitute its prey ; and I have seen the
Sarsia in confinement seize with the mouth, and swallow,
a newly-hatched fish, notwithstanding the activity of the
latter. For hours afterwards, the little green-eyed fry was
visible, the engulfment being a very slow process ; but the
Medusa never let go its hold ; and gradually the tiny fish
was sucked into the interior, and passed up the cavity of
318 EVENIXGS AT THE MICROSCOPE.
the peduncle, becoming more and more cloudy and indis-
tinct as digestion in the stomach dissolved its tissues.
The greater portion of the food is by and by dis-
charged from the mouth ; the fluids which have been
extracted from it being on the other hand carried up
through the base of the peduncle, and distributed along
the four radiating vessels, conveying nutrition, supply
of waste, and growth to all parts of the system.
We may now liberate our little Sarsia, with thanks
for the gratification he has afforded us, to resume his
active play among his many companions. Meanwhile
we will look for one of another kind among the group.
Here is a pretty and interesting species. Active it is,
but less vigorously rapid in its movements, than either
the Bero'6 or the Sarsia. It is, as you see, something
less than a hemisphere, or resembling a watch-glass in
shape, about three-fourths of an inch in diameter. In
general character it resembles the Sarsia, but the pe-
duncle is small, never reaching to the level of the margin,
and its mouth is terminated by four expanding fleshy
lips, which are extremely flexible and versatile.
The four radiating vessels here carry, just before they
merge into the marginal canal, a dilatation of the com-
mon flesh, which, as you see, bulges out the surface of
the umbrella. We will examine one of these dilatations
with the microscope.
It is, as you perceive, occupied by a number of clear
globes, each of which has another minute globose body in
its interior. They are very diverse in size, some being-
very small, others comparatively large ; and it is to the
dimensions of these latter that the swelling of the surface
of the umbrella is due. These vesicles are the eggs of the
animal considerably advanced towards maturity ; and the
dilatations around the radiating vessels are the ovaries.
The margin, however, presents us with the most obvious,
and perhaps the most interesting, points of diversity from
THAUMAXTIAS.
JELLY-FISHES. 319
the Sarsia. In the little beauty before us, whose scientific
name, by the way, Thaumantias pilo-
sella, I have not yet told you, — the out-
line is fringed with about fifty short and
slender tentacles, each of which springs
from a fleshy bulb, in which is set a
speck of deep purple. These collec-
tions of coloured granules, which I have
already explained to be rudimentary
eyes, have a very charming effect ; and
give a beautiful appearance to the little creature, as if
its translucent crystalline head were encircled with a
coronet of gems.
You shall see them, however, under circumstances
which will make them appear more lustrously gem-like
still. Come with me, and I will carry the glass containing
our little Thaumantias into the next room. You need
not bring the candle, or what I am going to show you
will be quite invisible.
Take hold of this pencil, and, having felt for the glass,
disturb the water with it. Ha ! what a circle of tiny
lamps flash out ! You struck the body of the Thaumantias
with the pencil ; and instantly, under the stimulus of
alarm, every purple eye became a phosphoric flame.
Touch it again ; again the crown of light flashes out, but
less brilliantly; and each tiny lamp, after sparkling
tremulously for a moment, wanes, and the whole gradu-
ally, but quickly, go out, and all is dark again.
But it is tired of lighting up for nothing; or its gas is
exhausted; or it is become used to the pencil and is not
alarmed; or, — at all events you may knock it, and push
it, but it refuses to shine any more. Back with it then
to the microscope, and let us see if it possesses any other
points of interest for us there.
Yes : we have not exhausted the organs of the margin
yet. Between the tentacles which spring from bulbs
320
EVENINGS AT THE MICROSCOPE.
there are a good many more, far more minute, without
any bulbs; — from four to seven between every two of the
primary ones. We won't mind these, but, bringing the
margin itself into focus, and moving it along the stage
horizontally, we presently see one and another singular
organs. They are eight in all, two being placed, but
irregularly, in each of the four quadrants of the circle
formed by the radiating canals.
These are organs of hearing, very closely similar to
those which we see imbedded in the bosom of the Snail
and other Mollusca. Here they are comparatively large,
and unusually well furnished. Each is a semi-oval en-
largement of the flesh of the margin, in close connexion
with the walls of the marginal canal, hollowed so as to in-
close a capacious cavity, in which are placed a considerable
number, — from thirty to fifty in this individual — of oto-
lithes, or spheres of solid, transparent, highly-refractive
OTOLITHES OF THAUMATTTIAS.
substance. They are arranged in a double line, forming a
crescent, and those which are nearest the centre are larger
than those towards the extremities of the line. I believe
some observers have seen oscillatory and rotatory move-
ments among these spherules, as in the Mollusca; but I
have invariably found them motionless in all the species
of Medusa that I have examined, as you see them here.
One more little beauty from our stock, and we have
JELLY-FISHES. 321
done with these. There is one that moves among the
rest like a bead of coral, the smallest of all, yet the
most brilliant. Here is another, and here another of the
same sort; which has been named by Professor Edward
Forbes, Turris neglecta, because naturalists before him
had neglected to notice it, just as we have been doing,
engrossed by its larger brethren.
Beautiful as is this little gem; it is not so large as a
dried pea, scarcely larger than a grain of hemp-seed. It
is described as " mitre-shaped ;" in other words, it is a tall
bell, with the margin slightly bent inwards, and the sides
a little constricted. The umbrella is thick, and, being-
very muscular, is not so translucent as those we have
been examining; hence it has a pellucid white appearance.
But through this shines its chief beauty; the peduncle
is very large, and globose at the upper or basal part,
which is usually, as here, of a pale scarlet or rich orange
hue.
Imbedded in this orange-coloured flesh are seen many
points of a lovely rose-purple; which two colours blend-
ing together, and softened by their transmission through
the sub-pellucid umbrella, have a peculiar brilliancy.
But stay ! here I have one more advanced in age, which
will exhibit some peculiarities of interest in the economy
of these frail but charming creatures.
In this specimen, which is somewhat larger than the
former, the margin of the umbrella is a little turned
back, displaying more clearly the peduncle with its
brilliant ovaries. These, too, are more turgid, and the
rosy points are seen projecting from their interior, and
some of them even ready to fall. And look ! here on
the bottom of the glass are lying half-a-dozen or more of
similar purple points, whose rich hue renders them plainly
discernible, after a slight searching, to the unassisted eye
I will collect one or two with a tube of glass, and
submit them to your examination under the microscope.
Y
■'322 EVENINGS AT THE MICROSCOPE.
You now discern that these bodies are perfectly oval
in form. One might, indeed, call them eggs, — for
they perform the part of such organisms, — but that
they have soft walls, covered on their whole external
surface with fine vibratile cilia, by the action of which
they are endowed with the power of free locomotion.
We see them, in fact, gliding about the water of the
live-box under view, with an even and somewhat rapid
motion, which appears to be guided by a veritable will.
Under this power they are seen to be of a soft rich lake-
crimson hue, all over.
These little gemmules have a somewhat romantic history
of their own. I am afraid that these we see are too
recent to afford us any help in tracing it, and therefore
I must be satisfied with telling you what I have observed
of it on former occasions.
After the beautiful little Coral Jelly has swum about
a few days, the umbrella begins to turn outward and
backward, and to contract more and more, until at
length it lies in shrivelled folds around the top, leaving
the whole peduncle exposed. Long before this, the
creature has lost its power of swimming, and lies help-
less on its side upon the bottom. Meanwhile the
orange ovaries have swollen; the purple gemmules
have become developed, and have gradually worked their
way through the ovaries, and fallen one by one upon the
bottom. There then they glide about for a little time,
perhaps for a day or so, by means of their vibrating cilia.
At length each little gemmule loses its power of
wandering, its motion becomes feebler and more inter-
mitted, and finally ceases altogether. The little being
now rests on some solid body, — a stone or a shell, — to
which it firmly adheres. Its two extremities grow out,
adhering as they extend, and sometimes branching, but
still in close and entire contact with the support. At
length, after a day or two, from some point of the upper
JELLY-FISHES. 323
surface of this creeping root, a kind of wart buds forth,
and soon grows into an erect slender stem, which
presently divides into four straight, taper, slightly
divergent tentacles, which grow straight upward to a
considerable length. The whole structure retains the
rich purple hue of the original gemmule.
Beyond this point I have not pursued the history of
the little Turris from personal observation; nor am I
aware that any naturalist besides has studied the de-
velopment of this particular genus. But the history of
other genera is known; and as the phenomena they
exhibit are quite parallel to those which I have been
describing, so far as these have been traced, we may
fairly conclude that there is the same parallelism in the
subsequent stages.
Assuming this, then, the little crimson stem with four
rays, — a veritable polype, — buds four more tentacles in
the interspaces, making the total number eight; these in
like manner increase progressively to sixteen, thirty-two,
and sixty-four. It now possesses a close resemblance to
the Hydra of our ditches, only having more tentacles;
&nd, like it, the Medusa-larva buds forth from its sides
young Hydra-like polypes, which take the form of their
immediate parent, fall off, attach themselves, bud forth
more, and so on. All these catch living prey with their
tentacles, swallow them with their mouths, and digest
them with their stomachs, exactly like real polypes, and
thus produce generation after generation of similar
beings.
Years may pass in this stage, during which number-
less polypes are formed. At length the original stock,
or any one of its descendants, takes-on an important
change. Its body lengthens, and becomes cut as it were
into a number of rings, as if tied tightly round with
thread, or like the body of an Annelid. These segments
become increasingly distinct, until at length each is seen
y 2
324
EVENINGS AT THE MICROSCOPE.
to be a shallow cup, notched at its margin, and sitting in
the concavity of the one next below it. This structure
is developed first in those at the free extremity of the
polype, and progressively downward; and the terminal
cups are nearly free, rocking in their successors with
every wave, while the lowest segments are scarcely
visible as such.
At length the extreme cup rocks and oscillates until
the slender thread of connexion is snapped, and it is free.
It at once turns itself over, so as to present its concavity
TURBIS AND ITS YOUNG.
downwards, and, contracting its margin with the well-
known pulmonic spasm, shoots away with the movement
as well as the form of a veritable Medusa. The little
progeny has at length, after passing through so many
changes, returned to the image of its parent.
Such are, in brief, the phenomena of one of the most
remarkable series of facts that modern zoology has dis-
covered, and which have been propounded under the
title of the Law of Alternation of Generations.*
See pages 333, 334, infra.
ZOOPHYTES. 325
CHAPTER XVIII.
ZOOPHYTES.
It is pleasant to go clown to the shore on a bright autum-
nal morning at low water, when the tide has receded far,
exposing great areas of wet sand, and wildernesses of
rugged rocks draped with black and red weed. It is
pleasant to make our way on cautious foot round some
frowning point whose base is usually beaten by the
billows; to travel among the slippery boulders, now leap-
ing from one to another, now winding between them,
now creeping under their beetling roofs; to penetrate
Avhere we have never ventured before, and to explore
with a feeling of undefined awe the wild solitudes where
the hollow sea growls, and the grey gull wails. It is
pleasant to get under the shadow of the tall cliffs of
limestone, to creep into low, arching caves, and there to
stoop and peer into the dark pools, which lie filled to the
brim with water as clear as crystal, and as unruffled as a
well. What little worlds are these rugged basins! How
full of life all unsuspected by the rude stone-cutter that
daily trudges by them to and from his work in the marble
quarry of the cliff above ! What arts, and wiles, and
stratagems are being practised there ! what struggles for
mastery, for food, for life ! what pursuits and flights !
what pleasant gambols! what conjugal and parental
affections ! what varied enjoyments ! what births ! what
deaths ! are every hour going on in these unruffled wells,
beneath the brown shadow of the umbrageous oar-weed,
•or over the waving slopes of the bright green Ulva, or
among the feathery branches of the crimson C eramiiamf
326 EVENINGS AT THE MICROSCOPE.
I have just been exploring some of these rock-wells,
and have rifled them of not a few of their living treasures,
bringing home the spoils, that you may share with me in
the enjoyment of examining them.
The Zoophytes* are here in their glory. Such places
as those I speak of are the very capitals of the zoophytic
nation. Look at this great leaf of the fingered Tangle :
see how its broad olive-brown expanse is covered with
tiny forests of white branching threads, which spread and
spread till they run off into the fingers of the much split
leaf; and not only on one side, for the under surface is as
densely clad with the shaggy burden as the upper; the
smooth leathery tissue being covered with a network of
creeping roots, branching and radiating everywhere, like
the railways on Bradshaw's map.
This double forest is wholly composed of a single species,
called Laomedea geniculata ; nay, I believe it is but one
single individual. That is to say, the whole of these mul-
titudinous ramified threads and stems, with their innu-
merable polypes,! have all extended by gradual though
rapid growth from a single germ ; and all are connected
even now, so that a common life pervades the whole.
But we will look awhile at it in detail, till we have
mastered its external features, and then I will tell you
something of its history and economy.
With the unassisted eye we can discern plainly enough
the outline and plan of this compound organism. Along
the smooth and slippery surface of the olive weed runs a
* From the Greek £u)oi'(zoon), an animal, and tpvrbv (phuton), aplant.
A term applied to a large class of animals bearing 'polypes, and whose
entire skeleton, called a poly par -y or polypidom, more or less resembles
a plant or tree in its appearance and growth.
The term Cozlenterata is now substituted for this in systematic natural
history. See Prof. Greene's excellent " Manual of the Anim. Kingd."
ii. Lond. 1861.
t From the Greek 7to\vq (polus), many, and ttovq (pous), afoot. A
low order of animals having numerous tentacles or feelers round the
mouth, and often bearing a strong resemblance to flowers.
ZOOPHYTES. 327
fine thread of a pellucid white appearance, so firmly
adherent that if you attempt to remove it with a needle's
point, you find that you only tear either the leaf or the
thread. The course is generally in a straight line, but does
not ordinarily pursue the same direction far, commonly
turning off with an abrupt angle at intervals of about
an inch; and thus meandering in a zig-zag fashion, very
irregularly, branching frequently, and uniting with a
thread already formed, when the creeping one has to
cross it.
Thus the basal network is formed; but, meanwhile,
from every angle, and often from intermediate points, a
free erect thread has shot up, like the stem of a tiny
plant, to the height of an inch, rarely more ; not, however,
straight, but with frequent zig-zag angles, whence the
name geniculata, or " kneed." At every angle a slender
branch is sent forth, pursuing the same direction as that
of the joint from the summit of which it issued, and
terminating in a tiny knob. In the angles of some of
these branchlets are seated oblong vesicles, twice or
thrice as large as the terminal knobs. And this is pretty
well all that we can make out with the naked eye.
Cutting carefully off with scissors a narrow strip of the
leaf, I drop it into the parallel-sided cell of glass half-filled
with sea-water, and examine it first with a low power
and afterwards with a higher. We now see that the
creeping thread is a tube of horny substance, flattened
on its under side, and that the erect stems and their
branches are similar tubes, whose cavities are in free com-
munication with that of the creeping root. The wall is
thin, and perfectly transparent and colourless ; the white-
ness of the whole being dependent on a soft medullary
core of living jelly, which permeates the whole structure,
on which the horny sheath is, as it were, moulded.
This medulla is pierced with a canal, through which a
fluid circulates, carrying along numerous minute granules
328
EVENINGS AT THE MICROSCOPE.
with a quivering, jerking motion; this is doubtless the
nutrient fluid conveying the products of digestion to
every part of the common structure.
Where the branches issue from the angles of the
stem, the medulla, and conse-
quently the horny sheath, is
dilated into a knob; immedi-
ately above this there is a
joint-like constriction in the
tube, and the branch itself
is insected by four or five
such constrictions, so as to
form as many rings. Its ex-
tremity then expands into an
elegant cup or vase, of ex-
treme tenuity and trans-
parency, shaped like a wine-
glass, with the rim undivided,
but so thin and subtle as to
be seen with the greatest
difficulty.
These cups, or cells, are
each the proper habitation
of a polype, which is nothing
else but the termination (in this direction) of the living,
growing, vascular pith. The latter becomes exceedingly
attenuated, in order to pass through a very narrow orifice
in the centre of a horny diaphragm, or sort of false bottom,
which passes across the lower part of each cell. It then
dilates into a soft, contractile animal, whose body — but
look for yourself; for here, full in the field of the micro-
scope, is one expanding in the highest vigour and beauty.
It is a long trumpet-shaped body of granular flesh, the
mouth of which just reaches the brim of the cup, over
which it spreads on all sides. From its margin spring
some eighteen or twenty tentacles — the exact number
LAOilEDEA.
ZOOPHYTES.
329
varying in different individuals — arranged in one or two
close-set circles, like a crown. These organs, which, as
you see, fall into elegant double curves, like the branches
of a chandelier, are roughened with knobbed rings, some-
thing like the horns of a goat; this structure we will
presently submit to more close examination.
In the midst of the space surrounded by the tentacular
crown there is protruded, at the pleasure of the animal,
a large, fleshy, funnel-shaped mouth, the lips of which
are highly sensitive, continually changing their form;
protruding, contracting, bending in upon themselves,
now closing, now opening the mouth, and, as it were,
testing the immediate vicinity, like a very delicate organ
of some unknown sense.
The whole polype is much too minute for us to attempt,
with any probability of success, the amputation of one of
the tentacles with scissors. But by
cutting off a polype, cell and all, and
putting it into the compressorium,
we may be able, by means of the
graduated pressure, to flatten the
whole, and thus discern the gnarled
structure of the tentacles. A very
high magnifying power is needed
for this.
Here, then, we have one of the (
tentacles flattened between the glass
plates,but still retainingits integrity.
We find that the thickenings are
similar in character to those of the
tentacles of Sarsia, which we lately
observed. They are, in fact, accu-
mulations of cnidce, those peculiar
weapons of power, which T shall presently describe in
full; but here they are symmetrically arranged in single
rows, each pointing upward and outward.
TENTACLE OF LA01IEDEA ;
flattened.
330 EVENINGS AT THE MICROSCOPE.
To return to the living specimen on the leaf : you see
seated in the angles of the branches, here and there,
elegant urn-shaped cells, larger than the polype cells, each
with a sort of shoulder and a narrow neck. The common
marrow passes from the joint into the bottom of these,
and then extends through the centre till it reaches the
mouth. In some of the urns this forms merely a slender
column, expanding at the mouth; but in others it
enlarges at irregular intervals into large knobs or masses
of granular flesh, which are confusedly grouped together,
eight or ten in one capsule. This latter is the most
interesting condition; let us watch it.
While doing so, let me inform you that these urns are
the reproductive organs ; and the fleshy masses are
embryos of peculiar character, which are developed out.
of the nutrient medulla. The largest of those now under
observation is, as you see, moving, and slowly working
its way out of its glassy prison. Two or three flexible
finger-like bodies are protruding from the orifice of the
urn, and more are joining them : we see they are tentacles,
protruded in a loose bundle, just as the polype emerges
from the cell.
It is a somewhat slow process; but at length the fleshy
mass squeezes itself forth, as if pushed out by some con-
tractile force behind; while we see the fluids, carrying-
granules, run into the parts of the tentacles which are
already free. The embryo is liberated.
For a few seconds it appears helpless, and falls through
the water in a collapsed state, so that we cannot discern
its proper form. It gives a spasmodic contraction or
two, feeble at first, then more vigorous; the tentacles
lengthen, the body expands, and — lo ! it is not a Polype,
but a Medusa !
And now take your eye for a moment from the micro-
scope, and glance at this glass jar, in which the oarweed
with its colony of Zoophytes has been standing for a few
ZOOPHYTES. 331
hours. Hold it between your eye and the light; do you
not see that the water is alive with tiny dancing atoms 1
Hundreds are there, playing and pumping through the
fluid with a sort of napping motion, which, when you
get one sidewise in clear view, will not fail to remind
you of the flagging flight of some heavy-bodied, long-
winged bird. These are the Medusa-shaped progeny of
the Laomedea.
But let us return to the one of which we have just wit-
nessed the birth, and which is still flapping to and fro in
the narrow glass trough. You see a pellucid, colourless
disk or umbrella of considerable thickness, about one-
sixtieth of an inch in diameter in its average state of
expansion. Its substance has a reticular appearance, pro-
bably indicating its cellular texture. Internally, the disk
rises to a blunt knob in the centre, whence four vessels
diverge to opposite points of the margin. These form
elevated ribs, the surface being gradually depressed from
each to the centre of the interspace. Externally, the
centre of the disk is produced into a fleshy peduncle,
having a narrow neck, and then expanding into a sort of
secondary disk, of a square form, with the angles rounded.
This organ, which is capable of varied, precise, and
energetic motions, corresponds to the peduncle of a true
Medusa, the angles being the lips. These lips, which
correspond in their direction to the four internal ridges,
are very protrusile; and, when the little animal is active,
are continually being thrust out in various directions,
sometimes everted, but more commonly made to approach
each other in different degrees ; sometimes one being
bent-in towards the centre, sometimes all closing-up
around a hollow interior. These four lobes, thus per-
petually in motion, and changing within certain limits
their form and their relation to each other, remind one of
the lips or the tongues of more highly organised animals.
The substance of this peduncle appears to be delicately
332 EVENINGS AT THE MICROSCOPE.
granular ; but there is a very manifest tendency to a
fibrous character in its texture, the fibres being directed
from the exterior towards the interior, supposing the
lobes to have their points in contact.
Let us now look at the margin of the disk. Here are
attached twenty-four slender tentacles, six in each qua-
drant formed by the divergent ribs, or radiating canals.
Each tentacle springs from a thickened bulb, which is
imbedded in the margin of the disk ; it is evidently
tubular, but the tube is not wider in the bulb than in the
filament. The general surface is rough, with projecting
points, which in some assume a very regular spinous
-appearance, and the tentacle terminates in a blunt point.
The discal part of the bulb is fringed with a row of minute
bead-like spherules. Around the edge of the circumference
•of the disk, on the exterior, are arranged eight beautiful
and conspicuous vesicles, or organs for hearing. They are
placed in pairs, those of each pair being approximate, and
appropriated to each of the quadrants of the circle. Each
of these organs consists of a transparent globe, not enve-
loped in the substance of the disk, but so free as to appear
barely in contact with it: it contains a single otolithe,
of high refractive power, placed, not in the centre, but
towards the outer side. The inexperienced naturalist, on
first seeing these organs, would unhesitatingly pronounce
them eyes, and the otolithe, or ear-stone,* the crystalline
lens. They are, however, pretty certainly, rudimentary
organs of hearing; the crystalline globule or otolithe
being capable of vibration within its vesicle. Their
•exact counterparts are found in many of the smaller
Medusae, as we lately saw in the Thcmmantias.
The disk is endowed with an energetic power oc con-
traction, hy which the margin is diminished, exa 3tly like
that of a Medusa swimming; and the tentacles have also
the power of individual motion, though in general this is
* See note on page 56.
ZOOPHYTES. 333
languid, their rapid flapping being the effect of the con-
traction and expansion of the disk, whereby the margin
is moved quickly backwards and forwards, carrying the
tentacles with it. Occasionally, however, all the ten-
tacles are strongly brought together at their tips, with a
twitching, grasping action, like that of fingers, which is.
certainly independent of the disk, and may be connected
with the capture of the prey.
Now every detail of the structure here, as well as the
general form, appearance, and habits, agrees with the
small naked-eyed Medusae, so closely that if we had not
witnessed the birth of the little creature from the repro-
ductive cell of a Laomedea, we should, w^ith unhesitating
confidence, have pronounced it a true Acaleph. The ped-
uncle, it is true, seems out of place, being on the outside of
the dome, instead of hanging suspended from its interior ;
but this difference is only apparent, and arises from the
circumstance that the disk is reverted. If you suppose
the edge of the disk to be turned in the opposite direc-
tion, you will have the peduncle in its proper place : the
umbrella in these specimens is carried within, and the
sub-umbrella without ; an inversion which is probably
accidental, or, at least, unimportant.
Comparing now this strange production of a Medusa by
a Polype, with Avhat I lately told you of the production of
Polypes by a Medusa (as in the case of the lovely little
Turris), you will have some acquaintance with the won-
drous phenomena which have of late years been surprising
and interesting naturalists, viz., those of the Alternation
of Generations ; in which, as Chamisso, the first dis-
coverer of the strange facts, observed, — " a mother is not
like its daughter, or its own mother, but resembles its
sister, its grand-daughter, and its grandmother." The
Polype gives birth to a generation of Medusre which lay
eggs, which develop into Polypes. The Medusa, on the
other hand, lays eggs (gemmules), which develop into
334 EVENINGS AT THE MICROSCOPE.
Polypes, "which at length divide themselves into colonies
of Medusse.*
At first you will perhaps see nothing remarkable in
another object which I collected in my rock-ramble to-
day. A Hermit-crab in an old Natica shell ; both
common things enough. Yet look more narrowly. The
greater portion of the shell is not smooth, has no such
porcelain-like polish as the Natica usually has, but is
clothed with a sort of downy nap, a coarse sponginess of
a greyish hue, splashed with yellowish and pink tints.
The shell is invested with Hydractinia.
We restore the strange partnership, — shell, fleece, and
crab, — to the glass of sea-water ; where we soon see the
whole tumbling about the bottom in uncouth agility.
Assist your eye with this pocket-lens, and look again.
The shaggy nap upon the shell now bristles with tall
slender polypes, crowded and erect, like ears of corn in
a field.
No high magnifying power is necessary to furnish us
with considerable entertainment from this populous
colony. The polypes stand individually nearly half-an-
inch in height : each consists of a straight slender column,
surmounted by eight straight rod-like tentacles, four of
which stand erect, slightly diverging, and the other four
alternating with these at their origin, extend horizontally
like the arms of a turnstile.
The rough jolting of the crab over the stones the ex-
panded polypes bear with equanimity ; they are used to
* Since this work was published, many efforts have been made to
explain, and to bring into harmony with what were supposed to be the
laws of generation, these strange facts, which seem to subvert all our
notions of individuality. Steenstrup's phrase is now by common
consent abandoned : there is no alternation of generation proper.
That hypothesis which regards the phenomena as those of metamor-
phosis, the fixed condition (Laomedea) being analogous to the larva,
the free-swimming (Medusa) to the adult, is one of the most plausible ;
but an attempt to apply it in all the cases shows it to be untenable.
(See Greene, Coelenterata, p. 76.)
ZOOPHYTES. 335
it; and though their tentacles wave and stream hither and
thither, they are not retracted on this account. But just
touch with the point of the pencil in your hand any part
of the shaggy fleece, and instantly the whole colony retire
together, as if by a common impulse, apparently shrinking
into the substance of the shell. Yet they soon re-appear,
one after another quickly protruding its closed tentacles,
which are presently expanded as before.
The explanation of this phenomenon is, that the whole
colony of polypes are but the free points, or feeding mouths,
of a common living film, which invests the shell; just as,
in Laomedea, the polypes that inhabit the vase-like cells
are the off-shoots or free points of the common medulla.
The investing film will sometimes in captivity spread
upon the glass side of a tank, and there develop all the
polypes and organs proper to the complete organism.
When this is the case, an admirable opportunity is pre-
sented for studying with ease and precision the economy
of the creature; and it is to the skill with which Dr. T.
Strethill Wright has availed himself of such an oppor-
tunity* that I am indebted for the chief part of the facts
that I am going to tell you, connected with the form and
appearance, of which you can here judge for yourself.
The spreading film or polypary is a thin coat of trans-
parent jelly, slightly coloured with various tints, which
secretes and deposits within its substance a still thinner
horny layer of chitine. This rises here and there into
numerous spines and points, which are curiously ridged
with toothed keels; and these ridges run in various
directions over the horny layer also, making a fine net-
work over it. The investing flesh, however, fills up all
the cavities and areas so inclosed.
The mode in which the polypary increases is by throw-
ing out from its edge a creeping band, exactly analogous
to the root-thread of the Laomedea. This "propagative
* See "Edin. New Philosophical Journal," for April, 1857.
336 EVENINGS AT THE MICROSCOPE.
stolon, after leaving the point of its origin, increases
rapidly in diameter, and sends out irregular branches.
The tips of these branches are covered with a glutinous
cement, by which they attach themselves tenaciously to
glass, or other surface near them. Having attached them-
selves, they expand laterally, at the same time throwing
out finger-like prolongations, which, as they come in con-
tact with each other, coalesce, until a fleshy plate is found
adherent to the glass. Polypes are developed both from
the loose branches and the attached polypary; and the
latter is clearly seen to be permeated by a beautiful system
of anastomosing canals, connected with the hollow bodies
of the polypes. Within these canals may be detected an
intermittent flow of fluid, containing particles, the dancing
motion of which indicates the presence of ciliary action ;
and which, having passed in one direction for a short time,
are arrested, and, after a slight period of oscillation, be-
gin to flow in an opposite direction."
The polypes which are developed from this living
carpet are not all of the same form. ISTo fewer than five
distinct sorts exist, at one and the same time ; and I
doubt not we shall be able to find and to identify them
all, on this well-grown specimen.
First, there are the alimentary polypes, which we have
already cursorily glanced at. Within the space inclosed
by the two circles of tentacles, there is a mouth with soft
protrusile lips, which can be pushed out and folded back,
so as to hide tentacles, column, and all.
Scattered among these we see numerous polypes,
which agree in general form with these, but with some
remarkable subtractions and additions. They have no
mouth nor stomach, and the tentacles are reduced to the
smallest possible warts or protuberances like small teeth
on the dilated tip. But the additions are still more
peculiar. From the middle part of the column a number,
from four to nine, of great oval sacs project, each attached
ZOOPHYTES. 337
hy one end, while the other stretches out horizontally,
thus surrounding the slender column. Each of these
■sacs is an ovarian capsule, and contains several ova of a
brilliant yellow or crimson hue. Thus we have the
second form, that of the reproductive polypes.
In some places single ovarian capsules stand up alone
from the fleshy carpet, agreeing in every respect with
those which we have just examined, except that they
are sessile, instead of being carried by a polype.
The fourth form is that of the tentacular polype. Here
and there, from amidst the forest of shorter polypes, both
alimentary and reproductive, white threads are seen pro-
truding, which extend to a length four or five times as
great as theirs, and hang down or loosely float in the
water. They are found on the outskirts of the whole
compound structure, and at each extremity of the long
diameter of the mouth of the supporting shell ; so that
they must, in their natural condition, reach to the ground,
along which the crab-tenanted shell is carried, enabling
the Zoophyte to seize and appropriate the atoms scattered
by the crab whenever he takes his meals. The tips of
these organs are covered with a dense pavement of large
thread-cells; and they must doubtless perform the office
of general purveyors to the composite animal.
But still more remarkable, more extraordinary than all
we have been considering, are the objects which are now
in view in the field of the microscope. You see a number
of bodies, which Dr. Wright calls ophidian or spiral
polypes ; and which, as he truly observes, are " like small
white snakes, closely coiled in one, two, or three spirals,
and grouped immediately round the mouth of the shell."
The habits of these polypes are still stranger than their
forms. " When touched they only draw their folds more
closely together. But if any part of the polypary, however
distant from them, be irritated, the spiral polypes uncoil,
extend and lash themselves violently backwards and for-
338 EVENINGS AT THE MICROSCOPE.
wards, and then quickly roll themselves up again ; and
that not irregularly or independently of each other, but
all together, and in the same direction, as if moved by a
single spring. A violent laceration of the polypary causes
these polypes to remain extended and stretched like a
waving and tremulous fringe across the mouth of the shell,
for several minutes. The ophidian polypes (evidently a
barren modification of the reproductive polype) are never
found in any other situation on the polypary than in that
before described, or round the margins of accidental holes
in the shell. They have no mouth and the tentacles are
rudimentary. The walls of the body are very transparent,
from the extreme vacuolation of the inner tissue. The
muscular coat, as might be expected, from the active move-
ments of the polypes, is highly developed, and forms a
beautiful object on the dark polarised field of the micro-
scope, each spiral coil shining out as a bright double
ring divided by four dark sectors. The outer tissue of
the whole body and tentacles is crowded with the larger
thread-cells. The ophidian polypes are, doubtless, organs
of defence or offence, like the motile spines and bird's
head processes of the Polyzoa, or the pedicellarise of the
Echinodermata ; but it is difficult to assign a reason for
their peculiar situation. They vary much in number
and size, in different specimens of Hydractinia, but are
rarely altogether absent."*
The reflections of the able zoologist who first called
attention to these varied developments, and his compari-
sons of them with those of another polype-form which we
have lately been observing, are so interesting and instruc-
tive that you will not deem it needful that I should
apologise for citing them. " In our consideration of the
Hydractinia" he observes, " our attention is arrested by
the multitude of objects grouped together to constitute a
single animal, their variety in form, and the sympathy
* Dr. Wright, op. cit.
ZOOPHYTES, 339'
which subsists between the different parts. The singular
spinous skeleton; the expanded membrane of the polypary,
with its beautiful internal network of tubes and delicate
peripheric prolongations; the alimentary polypes, some
white and filiform, others thick, fleshy, crimsoD, or yellow
sacs, obligingly everted, to expose their interior to our
microscopic eye : the reproductive polypes, with their
richly coloured generative sacs ; the sessile generative
organs of the polypary; the ophidian polypes, coiled in
neat spirals when at rest, but starting into furious action,
like a row of well-drilled soldiers, when injury is in-
flicted on the body to which they are attached; and lastly
the tentacle polypes, floating in the water like long and
slender threads of gossamer, or dragging up heavy loads of
food for the common good; — these, together with the inti-
mate relation and sympathy subsisting between the
polypary and its associated organs, all combine to form
an object of the highest interest, and indicate that, in
this fixed yet travelling zoophyte, we have a type of struc-
ture transitional between the dentritic Hydroidce and the
more highly organised Acaleph* In the simplest acale-
phoid form, such as the medusoid of C omjianularia [or
Laomedeaj (which is nothing more than an extension of
the polypary specially organised for independent and
motile life), we have (as in Hydractinia) an expanded
polypary, represented by the umbrella, and permeated by
vascular tubes, from the confluence of which last spring,
at the centre, the tenticular polypes, various in number;
and between them the reproductive polypes, represented
by the sessile generative sacs."f
You see here a jar, on the glass side of which are traced
a number of very fine white lines, barely discernible by
* From the Greek aicaXiifyr) (akalephe), a nettle, applied to animal
known under the common name of •jelly-fishes and sea-nettles, from
their causing the sensation of stinging when handled.
f Dr. Wright, op. cit.
z 2
340 EVENINGS AT THE MICROSCOPE.
the unassisted eye. But by the aid of the lens you see
that each line is a long and slender thread, which creeps
along the glass, and at length starts out from it free for
a short distance, and is then terminated by a long club-
shaped body, which carries at its extremity four horizon-
tally divergent organs, like the arms of a turnstile.
Tracing down the threads to their lower extremities, you
see that they are branches of one thread, which creeps
irregularly over a filamentous sea-weed growing from a
stone in the jar. The sea-weed had been in the vessel
for several weeks, and the water having been undisturbed,
the knobbed thread, which was originally confined to
the plant, continued to grow, and, coming in contact with
the glass, spread upon it. Many other threads have
extended from the creeping root, some of which stand
up freely in the water, with their knobbed extremities
floating in the wave.
This is one of the Polype tribe, named Stauridia pro-
ducta, and as its form and structure are interesting, we
will devote a few moments to its examination. We can
easily sever one or two of the freely floating threads,
and transfer the amputated portions to one of the live
boxes of the microscope. The motions and appearance of
the club with its organs will be, for a while, little
affected by the violence.
The long cylindrical thread is inclosed in a transparent
horny tube, which, however, so closely invests it, that it
is with difficulty distinguished. The club-shaped head, or
individual polype, is an enlargement of the thread, which
protrudes from the investing tube. It is swollen in the
middle and rounded at the end ; and many of the heads,
which are more ventricose than the rest, contain a bubble
of air in the centre. This air is doubtless taken-in at the
mouth, which is situated at the extremity ; for, though
you can discern no perforation, yet there is an aperture
capable of being opened widely at the pleasure of the
ZOOPHYTES. 341
animal, and surrounded by protrusile, contractile, and
expansile fleshy lips. I have several times seen this
mouth opened, and partly turned outwards, in kindred
species ; and once I had an opportunity of witnessing a
quite unexpected use to which it was applied, viz., that of
a great sucking disk. I had put the animal into such a
live-box as this ; the two glass surfaces being just suffi-
ciently wide apart to allow it free liberty to turn about in
all directions as far as it wished. On my looking at it
after a momentary interval, I saw that the extremity had
suddenly become a large circular disk of thrice the dia-
meter of the body : its substance was gelatinous, full of
granules, arranged concentrically. I neither saw this disk
evolved nor retracted ; but after some time, on looking at
it, the same phenomenon was repeated. In order to obtain
a better sight of it, but without suspicion of what I was
about to effect, I slightly turned the tube of the box,
carrying with it the sea- weed to which the polype was
attached, my eye upon it attentively observing all the
time. The base of the polype moved away from its posi-
tion, but the broad disk was immovable. I continued to
turn the upper glass, until at length the body was dragged
out so as to be considerably attenuated ; still the disk
maintained its hold on the lower glass, with no other
change than that of being elongated in the direction in
which it was dragged. At length it slowly gave way, and
resumed its original shape by gradual and almost imper-
ceptible diminution of the circumference.
Around this expansile, but now fast closed mouth, you
observe four tentacles, radiating in a plane at right angles
to the axis of the thread, towards the four cardinal
points; they are long, slender, straight, and each is
terminated by a globose head of considerable size, re-
sembling the arms of certain screw-presses, which are
loaded with terminal globes of metal to increase their
impetus when turned.
342
EVENINGS AT THE MICROSCOPE.
The structure of these tentacles is very interesting.
The stem contains a core
or central chain of large
cells, which take a some-
what square outline from
mutual pressure. The sur-
face is roughened with
small swellings, from each
of which projects a long
and extremely attenuated
hair (palpocil), which is
probably a very delicate
organ of touch. The ter-
minal sflobe is filled with
proportionately large oval
vesicles, each with a cen-
tral cavity, which are
arranged in a divergent
manner around the centre,
so that their tips shall
reach the surface of the globe ; these are those potent
weapons of offence called thread-cells (cnidce). The sur-
face of the globe is covered with short thick palpocils,
which Dr. T. S. Wright considers as prehensile organs.
"These papocils arise, each as a somewhat rigid process,
from the side of one of the large thread-cells, buried in
the head of the tentacle ; and they probably convey an
impression, from bodies coming into contact with them,
to the thread-cell, causing the extrusion of its duct."
Besides these globe-headed tentacles, there are, on the
lower part of the club-foot, four other organs similar in
every respect, except that they are not furnished with
heads, nor any terminal dilatation whatever. They pro-
ject horizontally as the knobbed- ones, but their origin,
and the respective lines of their radiation, are interme-
diate or alternate ; in other words, if we consider the
STAUKIDIA.
ZOOPHYTES. 343
globe-heads as pointing N., E., S., and W., the simple
ones point N.E, S.E., S.W., and N.W.
From the carefully made observations of several excel-
lent naturalists, as Dujardin, Steenstrup, Dalyell, Loven,
and others, it appears that this beautiful and elegant little
Polype gives birth to medusa-shaped young. Contrary,
however, to the rule in Laomedea, the Medusa is in this
case pushed forth as a bud from the side of the club,
without any protecting capsule. The process is exceed-
ingly like a plant developing a flower ; for the bud grows
until it at length expands blossom-like, and a beautiful
little umbrella-form Medusa is seen adhering to the
Polype. At length the brilliant little living flower
becomes detached; and, after swimming freely for a time,
discharges ova or gem mules from its ovaries, which
develop into a creeping root-thread, and finally into the
club-headed threads of the Stauridia.
Some objects which I have to exhibit to you are alto-
gether unique as to their appearance ; and, if you are not
as imperturbable as a Stoic philosopher or a Mohawk
Indian, will certainly excite both your risibility and your
wonder. For some little time I have been keeping in this
tank a specimen of that rather rare and very interesting
Sabella, the Amjihitrite vesiculosa of Montagu.* You see
it is a worm, inhabiting a sort of skinny tube, much
begrimed with mud, about two inches of its length being
exposed ; the remainder, or about as much more, being
concealed among the sand and sediment of the bottom.
A beautiful object is presented by the gill-fans of this
worm. These organs are always elegant, whatever species
of the genus is before us; but here, in addition to the
charm of the slender filaments, so delicately fringed with
their double comb-like rows of cirri, the tip of each bears
a dark purple spherule. That of the anterior filament on
each side is much larger than the rest, and forms a stout,
* "Linn. Trans.," xi. 19.
344 EVENIXGS AT THE MICROSCOPE.
globose, nearly black ball ; the others diminish to about
the twelfth on each side, where they disappear. These
balls are placed on the inner or upper face of the filament-
stem, at the point where the pectination ceases, the stem
itself being continued to a slender point beyond it, and
constituting the "short hyaline appendage" of Montagu.
From their great resemblance to the tentacle-eyes of the
Gasteropod Mollusca, I have little doubt that these are
organs of vision. If so, the profusion with which the
Sabella is furnished in this respect may account for its
excessive vigilance ; which is so great, that not only will
the intervention of any substance between it and the light
cause it to retire, but very frequently it will dart back
into its tube almost as soon as I enter the room, even
while I am ten feet distant.
It is not, however, to the tube, nor to the worm, that I
wish specially to direct your attention : yet it is necessary
that I say a preliminary word about the former. Ordi-
narily the tubes of these worms are formed of the fine
impalpable earthy matters (clay, mud, ifcc), held in sus-
pension in the sea, incorporated with a chitinous secretion
from the body of the animal; and therefore the surface of
the tube is always rough and opaque. But in this indi-
vidual case, the water in the vessel, probably owing to its
habitual stillness, not holding in suspension the particles
of mud that ordinarily enter into the composition of the
tube, the latest formed portion is composed of pure trans-
parent cJiitine, without any perceptible earthy element.
This clear terminal portion of the tube you may perceive
to be occupied by a curious parasite. About twenty
bodies, having a most ludicrously-close resemblance to
the human figure, and as closely imitating certain human
motions, are seen standing erect around the mouth of the
tube, now that the Sabella has retired into the interior,,
and are incessantly bowing and tossing about their arms
in the most energetic manner.
ZOOPHYTES.
345
As soon as you have recovered a little from your sur-
prise at this strange display, we will begin to examine the
performers more in detail. A slender creeping thread,
irregularly crossing and anastomosing, so as to form a
loose network of about three meshes in width, surrounds
the margin of the Sabella's tube, adhering firmly to its
exterior surface, in the chitinous substance of which it
seems imbedded. Here and there free buds are given
off, especially from the lower edge; while from the upper
threads spring the strange forms that have attracted our
notice. These are spindle-shaped bodies, about -^th of
LARES.
an inch in height, whose lower extremities are of no
greater thickness than the thread from which they spring ;
with a head-like lobe at the summit, separated from the
body by a constriction, immediately below which two
lengthened arms project in a direction towards the axis
of the tube.
Such is the external form of these animals, and their
movements are still more extraordinary. The head-lobe
of each one moves to and fro freely on the neck, the body
sways from side to side, but still more vigorously back-
ward and forward, frequently bending into an arch in
either direction; while the long arms are widely expanded,
346 EVENINGS AT THE MICROSCOPE.
tossed wildly upward, and then waved downward, as if to
mimic the actions of the most tumultuous human passion.
Whenever the Sabella protrudes from its tube, these
guardian forms are pushed oat, and remain nearly in con-
tact with the Annelid's body, moving but slightly ; but no
sooner does it retire than they begin instantly to bow for-
ward and gesticulate as before. These movements are
continued, so far as I have observed, all the time that the
Sabella is retracted, and are not in any degree dependent
on currents in the surrounding water, whether those
currents be produced by the action of the Annelid or by
other causes. They are not rhythmical ; each individual
appears to be animated by a distinct volition.
Applying a higher magnifying power than we have yet
used to the animals, we find that the head-lobe incloses a
central cavity ; that the arms are also hollow, with thick
walls, marked with transverse lines, indicating flattened
cells, and muricated on the exterior ; and that the body
contains an undefined somewhat opaque nucleus, doubt-
less a stomachal cavity.
I cut out, with fine scissors, a segment of the tube,
including two of the parasites, with the portion of the
network of threads that carried them. They have become
immediately paralysed by the division of the threads, but
those that remain on the tube are unaffected by the
violence. Subjecting one of the animals so cut out to the
action of the compressorium, with a power of 560 dia-
meters, the arms are seen to be formed of globose cells,
made slightly polyhedral, or many-sided, by mutual pres-
sure, set in single series. The interior of these organs
is divided by partitions, placed at intervals of about the
diameter. Some at least of the cells contain a small
bright eccentric nucleus.
When the tissues were quite crushed down by the pres-
sure of the compressorium, a quivering motion was visible
among the disjointed granules, but it was very slight.
ZOOPHYTES. 347
No trace of cilia, nor any appearance of ciliary motion,
was perceptible during life.
When I first discovered these strange beings, I was as
much astonished by what I saw as you are ; nor could I
imagine to what class of animals they were to be referred.
Neither did I know whether their presence on the tube
of the worm was a mere accident, or whether it indicated
a predominant instinct. On both these points, however,
light has been shed.
This larger Sabella tube was not the only one infested
with the parasites. I observed them on at least two
smaller specimens of the same species, in the same situa-
tion, and with precisely the same movements. The ex-
tremity of one of those smaller tubes I cut wholly off, and
placed in the live-box of the microscope. Two of the
parasites only were on it, which were active at first, but
in about an hour — probably from the exhaustion of the
oxygen in the small quantity of water inclosed — they de-
composed, or rather disintegrated, the outline dissolving,
and the external cells becoming loose and ragged, and the
whole animal losing its definite form.
One of these specimens, however, while yet alive and
active, afforded me an observation of value. I had al-
ready associated the form conjecturally with the Hydroid
Polypes, and was inclined to place it in the family Cory-
nidce, considering the arms to be tentacles, and the head-
lobe to be homologous with them in character, but ab-
normal in form. It appeared to be a three-tentacled
Coryne, with the tentacles simple instead of having heads.
But while I was observing the individual in question, I
saw it suddenly open the head-lobe, and unfold it into the
form of a broad shovel-shaped expanded disk, not, how-
ever, flat, but with the two halves inclining towards
each other, like two leaves of a half-opened book. This
immediately reminded me of the great sucking-disk
which, as I lately told you, I had seen evolved from the
3-48 EVENINGS AT THE MICROSCOPE.
obtuse summit of Stauridia producta, and confirmed my
suggestion of the natural affinities of the form.
Altogether unlike, in their shape, and in the unwonted
vivacity and peculiar human character of their movements,
all the other members of their natural family that I had
ever seen or heard of, these curious creatures have afforded
much entertainment, not only to myself, but to those
scientific friends to whom I have had opportunities of
exhibiting them. When I see them surrounding the man-
sion of the Sabella, gazing, as it were, after him as he
retreats into his castle, flinging their wild arms over its
entrance, and keeping watch with untiring vigilance until
he reappears, it seems to require no very vivid fancy to
imagine them so many guardian demons ; and the Lares
of the old Roman mythology occurring to memory, I de-
scribed the form under the scientific appellation of Lar
Sabellarum. You may, however, if it pleases you better,
call them " witches dancing round the charmed pot." *
The Polypes that we have as yet been looking at are
all of simple structure individually, though some of them
we have seen united into a very populous community of
compound life. \Ye will now look at some whose organi-
sation is of a higher, that is, more complex character.
On this old worm-eaten oyster-shell, which has been
dredged up from the bottom of the sea, you observe
several rounded lumps. They are of a cream-white hue,
of somewhat solid texture, tough and hard to the touch,
and studded all over with shallow depressions or pittings.
The largest of these is not more than an inch and a-half
in height, by two-thirds of an inch in thickness ; but
specimens often occur of twice or thrice these dimensions,
* Since my first discovery of this strange form in 1855, and my
memoir on it in the " Trans, of the Linnean Society," it has remained
unrecognised (and, indeed, somewhat suspected) for seventeen years.
In the summer of 1872, however, it again occurred to the observation
of the Rev. T. Hincks, who published a paper, with illustrations, on it,
in the Annals and Mag. of Nat. Hist, for Nov., 1872.
ZOOPHYTES. 349
and much more divided than this ; sometimes forming a
rude resemblance to a hand of stumpy, round fingers
of sodden flesh; whence the fishermen call the object
" Dead men's fingers," or sometimes, by a comparison
equally apt, " Cow's paps." To zoologists it is known as
Alcyonium digitatum.
Certainly there is nothing very attractive in these white
lumps as they now appear; but then they are now in un-
dress ; they do not expect to see company out of water.
Their drawing-room is beneath the waves, in some sub-
merged cave of ocean, where the sun's ray never pene-
trated, and where the only light is that dim green haze
reflected from the sand and shingle of the sea-floor ; save
when, on gala occasions, perchance, the Laomedece that
fringe the walls light up their myriads of fairy lamps, and
the tiny Medu&ce crowd into the watery festivities with
their elfish circlets and spangles of living flame. It is
then that the Cow's paps " take their hair out of paper,"
and display their loveliness to advantage.
Unfortunately, we have no card of invitation to these
submarine routs, but perhaps we may induce one of the
more juvenile of these beauties to indulge us, as a special
favour, with a sample of the effect ; particularly if we can
improvise a ball-room suited to the occasion. Let us try.
Selecting the very smallest specimen — a tiny thing no
larger than a pea — I try to detach it without injury, by
inserting the tip of my pocket-knife under the frilled
lamina of oyster-shell on which it rests, and working off
the fragment. I have succeeded : here it is, its attach-
ment unbroken : it is still firmly adherent to the severed
slice of shell, which is so small that I can drop it with its
burden into this narrow trough of glass. The whole con-
cern, trough, shell, and polype, is now to be dropped
into this capacious jar of freshly dipped sea-water, and
put away for an hour into a dark closet.
350 EVENINGS AT THE MICROSCOPE.
Now let us see the result. Yes, it is as I expected.
The united stimulus of the darkness and the sea-water
has acted on the Cow's pap, just as would the rising and
covering tide in its native cavern, after it had been left
exposed for some hours by the recess of the sea. It is
fully expanded, and is now as lovely as just now it was
unpleasing.
In the first place it is swollen to twice its former dimen-
sions, and has acquired at the same time a semi-pellucidity,
and a more delicate hue. But in the place of the pits on
the surface (there were not more than half-a-dozen in this
little specimen, which makes it more suitable for ex-
amination), it is covered with tall polypes, standing out
on all sides, of crystalline clearness and starry forms,
each eminently beautiful in itself, and surrounding the
whole mass with a sort of atmosphere of almost invisible
and impalpable lustre peculiarly charming.
Coy as these deep-water strangers are of displaying
their beauties in our glaring aquariums, they will bear
with equanimity a good deal of shaking, when once they
are expanded. Hence I may be able to transfer the
trough with its contents from the jar to the stage of the
microscope, and thus enable you to gaze on its details for
a little while, before the dull sensorium of the creature
is sufficiently warned of its ungenial position to cause it
to shut itself up and resume its ugliness.
As the protruded polypes are exactly alike, it will be
enough to confine our attention to one. It is an elevated
tubular column of translucent substance, terminating in
an expanded flower of eight slender pointed petals, which
spring outward with a graceful swell, so as to give the
form of a shallow bell to their general outline. The base
springs, like the foot of a tree, from the margin of a cell,
which penetrates the substance of the mass, into which we
can see far down, and into which the whole of the now
extended and expanded blossom was withdrawn when we
ZOOPHYTES.
351
first saw it, leaving only the shallow depression to mark
its situation.
The form of the column is in general that of the trunk
of a tree, or that of a long cone ; but there is a sudden
constriction just above the base, and another below the
point, where what may be called the flower expands. It
is the petals of this latter which constitute the principal
charm of this creature. They are, properly speaking, the
tentacles of the polype, answering in function and position
to those on the Laomedea, but differing considerably from
them in form. Each of the eight is thick and broad at its
POLYPES OF COW S PAP.
origin, and quickly tapers to a point : on each of two
opposite sides, viz., those which look towards the two
adjoining tentacles, runs a row of delicately slender
filaments, which at the middle part of the tentacle are
moderately long, but diminish regularly as they approach
either end. Starting from the side of the tentacle, in the
plane of its transverse diameter, these elegant pinna? pre-
sently arch downwards, but with perfect uniformity and
352 EVENINGS AT THE MICROSCOPE.
symmetry. By means of the high magnifying power which
I have now applied, each of these pinnre is seen to he
roughened with whorls of knobs, which are accumulations
of cnidse, analogous to those which we lately demonstrated
in the tentacle of Laomedea.
In the midst of the area surrounded by the petal-like
tentacles, a narrow slit opens into the stomach. This
organ is a flat sac, resembling an empty pillow-case
hanging down in the centre of the column, and open at
the lower end. From this end, which does not extend
to more than one-sixth of the depth of the cavity, three
threads, much twisted and irregularly thickened, spring
off at each side, and arch downwards, for a short distance.
These are the reproductive organs, which fringe the free
edges of as many delicate membranes which run up as
perpendicular partitions between the stomach and outer
wall, uniting with both, and thus dividing the space sur-
rounding the stomach into chambers open at the bottom.
There are eight of these septa (as the partitions are
called), but one on each side is destitute of the fringing
twisted thread.
The whole surface of the interior — the walls, the
stomach, and the septa — is clothed with fine vibratile
cilia, by the action of which constant currents are main-
tained in the water, which bathes every part of the cavity,
freely entering at the mouth. We can distinctly trace
these ciliary currents hurling along with irregular energy
the products of digestion, in the form of translucent
granules, especially along the edges of the septa.
Though the substance of the polype is soft and flexible,
it contains solid elements. Just below the expansion of
the tentacular blossom, we see imbedded in the skin a
vast mass of calcareous needle-like bodies called spicula.
Individually, these are very minute, and their form is
swollen in the middle, and taper at each extremity, the
whole roughened with projecting knots. Collectively, they
ZOOPHYTES.
353
are grouped in regular forms, crowded into dense masses
at the foot of each tentacle ; the mass having a three-
pointed outline, of which the central and largest point
runs up into the tentacle.
Towards the lower region of the column, spicula again
occur, scattered throughout the skin, and crowded into
groups, one on each interseptal space. These spicula are
of a very different shape from the upper ones; for they
form short thick cylinders, with each end dilated into a
star of five or six short branches, which are again starred
at their truncate ends.
If we now sacrifice our little Cow's pap to our scientific
SPICULA OF COWS PAP.
curiosity, we shall see something of its internal structure.
When removed from the water, the flower-like polypes
soon retract. I now cut open the mass lengthwise with
a keen knife ; and you see that it is permeated by canals
running from the base towards every part of the circum-
ference, dilating here and there to form the cells which
protrude and retract the polypes. This is a complete
system of water-supply : the surrounding sea-water, en-
tering at the mouths of the several polypes, bathes the
whole interior, and conveys oxygen and the products
of digestion together to every part of the compound
organism.
*> A
354 EVENINGS AT THE MICROSCOPE.
The fleshy substance which surrounds these canals is
of a loose, spongy character, and grates beneath the
knife : a circumstance which is owing to the predomi-
nance of the calcareous element here, as you will see
when I extract a small portion of it, and, laying it on a
slip of glass, treat it with caustic potass. The micro-
scope now reveals a large number of spicula, far larger
than those we have hitherto observed, and different
from either sort in form. These resemble very gnarled
branches of oak, with the branchlets broken off close to
their origin, leaving ra<™ed and starred ends.
SEA-ANEMONES : THEIR WEAPONS. 355
CHAPTER XIX.
SEA-ANEMONES : THEIR WEAPONS.
A very vast amount of the energy of animal life is spent
either in making war, or in resisting or evading it.
Offence and defence are sciences which the inferior
creatures can in nowise neglect, since all are interested
in one or other, and many in both ; and various are the
arts and devices, the tricks and stratagems, the instincts
and faculties, employed in that earnest strife which
never knows a suspension of hostilities. All classes of
animals, invertebrate as well as vertebrate, are warriors
by profession : the Spider is as carnivorous as the Lion,
and more strategic ; and the invisible Brachion is as
ruthless and insatiable as either.
An enumeration and description of the different kinds
of weapons, by means of which this truceless warfare is
carried on, would make a volume : nor would the subject
be then exhausted; for, since it enters so largely into the
very existence of animal life, the discoveries of advancing
science are ever bringing to light new forms and modifica-
tions, strange and unexpected contrivances, all calculated
to enhance our view of the inexhaustible resources of the
Lord God Omnipotent, " Who is wonderful in counsel,
and excellent in working."
I am going to bring under your notice this evening
some highly curious examples of animal weapons, of which
the very existence was until lately altogether unsus-
pected : yet so profusely distributed that they are
eminently characteristic of the animals we have been
2 a 2
356 EVENINGS AT THE MICROSCOPE.
recently considering — viz., the Medusae and the Zoo-
phytes. They have repeatedly fallen under our observa-
tion in examining the specimens of these creatures which
we had selected, but I had reserved the fuller elucidation
of them for an occasion in which they should come before
us under circumstances of such unusual development as
greatly to facilitate our researches. The weapons I speak
of are the cnidce or nettling-cells.
Look at thisbeautiful Scarlet-fringed Anemone (Sagartia
miniata), expanding to the utmost its disk and tentacles
in the clear water of the tank. I touch its body; instantly
the blossom-like display is withdrawn: the column closing
over it in the form of a hemispherical button, which goes
on contracting spasmodically. At the same time see these
white threads which shoot out from various points of the
surface; new ones appearing at every fresh contraction,
and streaming out to a length of several inches, re-
sembling in appearance fine sewing cotton twisted and
tangled irregularly.
Now the animal has attained its utmost contraction,
and the threads lengthen no more. But already they are
disappearing ; each is returning into the body by the
orifice at which it issued. It is, as you may see by exa-
mining it carefully with a lens, gradually contracting into
small irregular coils, at that end which is attached to the
animal ; and these little coils are, one after the other,
sucked in, as it were, through an imperceptible orifice.
Before the whole have disappeared, we will secure a
portion for examination. For this purpose I cut off with
sharp scissors about one-sixth of an inch of the extremity
of one of the threads, which now I transfer to a drop
of sea-water in the compressorium. These threads are
called acontia.
Examining this fragment under a low power of the
microscope, we readily see that, though at first it seems
a solid cylinder, it is really a flat narrow ribbon with the
SEA-AXEMOXES : THEIR WEAPONS.
357
edges curved-in, which can at pleasure be brought into
contact, and thus constitute a tube. Like all other internal
organs in these animals, its surface is richly ciliated,
and the ciliary currents not only hurl along whatever
floating atoms chance to approach the surface, but cause
the detached fragments themselves to wheel round and
round, and to swim away through the water. Though
there is not the slightest trace of fibre in the structure of
the acontiwni) when examined even with a power of eight
hundred diameters, the clear jelly, or sarcode, of which
POEIIOX OF ACONTIUH (flattened).
its basis is composed, is endowed with a very evident
contractility ; the filament can contract or elongate ; can
extend itself in a straight line, or throw its length into
spiral curves and contorted coils ; can bring its margins
together, or separate them in various degrees ; can per-
form the one operation at one part, and the other at
another, and thus can enlarge or attenuate the general
diameter of the cord, apparently at will. Some of these
changes can be effected even in the fragment detached
358
EVENINGS AT THE MICROSCOPE.
from the animal ; thus proving that the moving power,
whatever it is, is situated in the constituent tissue itself.
Under pressure the edges of the flattened acontium
appear to be thronged with clear viscous globules, over-
lapping one another, and protruding ; indicating one or
more layers of superficial cells, doubtless forming the
epithelium.* As the pressure is increased, these oozr
out as long pear-shaped drops, and immediately assume a
perfectly globular form, with a highly refractive power.
Below these is packed a dense crowd of cnidce, arranged
transversely.
Before we proceed to the examination of these curious
organs in detail, it may be well to devote a moment's
attention to the mechanism by
which the acontia themselves,
are projected from the body.
As this was first described (so
far as I am aware) by myself, t
I will take the liberty of citing
some of my observations on the
matter.
The omission of the acontia
is provided -for by the exist-
ence of special orifices, which
I term cinclides. The integu-
|(v ment of the body, in the Sagar-
tice, is perforated by minute
foramina, having a resemblance
in appearance to the spiracuht
of Insects. They occur in the
interseptal spaces ; opening a
communication between these
CINCLIDES.
* The thin, delicate cuticle or skin which covers all the free, un-
inclosed, internal surfaces of the body.
t In a memoir, entitled "Researches on the Poison Apparatus in
the Actiniadtc," read before the Royal Society, Feb. 4th, 1858.
SEA-ANEMONES : THEIR WEAPONS. 359
(and therefore the general visceral cavity) and the external
water. It follows that they are placed in perpendicular
rows ; but I have not been able to trace any other re-
gularity in their arrangement. So far as I have seen, they
are so scattered, that one, two, or even more contiguous
intersepts may be quite destitute of a cinclis. I would
not, however, attach too much weight to this negative
evidence, since the animal has the power of closing them
individually at will, and that so completely, that the
most careful scrutiny does not detect their presence.
Perhaps the best mode of examining them is to put a
small specimen of the S. dianthus or>S'. bell is into a narrow
parallel-sided glass cell, tilled with sea-water. After a
while the animal will be much distended; the exhaustion
of the oxygen impelling the Anemone to bathe its organs
with as large a quantity of the fluid as it can inhale.
The pellucidity of all the integuments will be thus
greatly increased. A strong lamp-light being now
reflected by means of the mirror through the animal on
the stage of the microscope, an inch or a half-inch object-
glass will probably reveal the orifices iu question with
much distinctness.
The appearance of the cinclides may be compared to
that which would be presented by the lids of the human
eye, supposing these to be reversed ; the convexity being
inwards. Each is an oval depression, with a transverse
slit across the middle. When closed, this slit may some-
times be discerned merely as a dark line — the optical
expression of the contact of the two edges ; but, when
slightly opened, a brilliant line of light allows the
passage of the rays from the lamp to the beholder. From
this condition the lids may separate in various degrees,
until they are retracted to the margin of the oval pit,
and the whole orifice is open.
The dimensions of the cinclides vary not only with the
species, and probably also with the size of the individual,
360 EVENINGS AT THE MICROSCOPE.
but with the state of the muscular contraction of the
integument, as, also, I think, with the pleasure of the
animal. In a small specimen of S. dianthus, I found the
width of a cinclis, measured transversely, yfyth of an inch ;
but that of another, in the same animal, was more than
twice as great, viz., y^yth of an inch. This was on the
thickened marginal ring, or parapet, which in this species
surrounds the tentacles, where the cinclides are larger than
elsewhere. Watching a specimen of S. nivea under the
microscope, I saw a cinclis begin to open, and gradually
expand till it was almost circular in outline, and -^^ th of
an inch in diameter. I slightly touched the animal, and
in an instant it enlarged the aperture to y^th of an inch.
In a specimen of & bellis, less than half-grown, I found
the cinclides numerous, and sufficiently easy of detection,
but rather less defined than in dianthus or nivea. They
occurred at about every fourth intersept, three intersepts
being blind for each perforate one; and about three or four
in linear series, but not quite regularly in either of these
respects. In this case they were about -~^th. of an inch
in transverse diameter — a large size ; and I measured one
which was even -g^th of an inch. By bringing the animal
before the window, I could discern the light through the
tiny orifices with my naked eye.
From several good observations, and especially from one
on a cinclis, widely opened, that happened to be close to
the edge of the parapet of a dianthus, I perceived that the
passage is not absolutely open, at least in ordinary; but
that an exceedingly thin film lies across it. By delicate
focussing, I have detected repeatedly, in different degrees
of expansion, and even at the widest, the granulations of a
membrane of extreme tenuity, and one or two scattered
cnidw, across the bright interval. On another occasion, in
the case of a cinclis at the edge of the parapet, a position
singularly favourable for observation, I saw that this subtle
film was gradually pushed out until it assumed the form of
SEA- ANEMONES I THEIR WEAPONS. 361
a hemispherical bladder, in which state it remained as
long as I looked at it. At the same time the outline of
the cinclis itself was sharp and clear, when brought into
focus further in. The film, whatever it be, is superficial,
and does not appear to be a portion of the integument
proper. I take it to be a film of mucus (composed of
deorganised epithelial cells), which is constantly in pro-
cess of being sloughed from all the superficial tissues in
this tribe of animals, and which continues tenaciously to
invest their bodies, until, corrugated by the successive
contractions of the animal, it is washed away by the
motions of the waves. As, however, one film is no
sooner removed than another begins to form, one would
always expect external pores so minute as these to be
veiled by a mucus-film in seasons of rest.
The pressure of this film is sufficient evidence that
the cinclides are not excretory orifices for the outflow of
the respired water in the manner of the discharging
siphon in the Bivalve Mollusca : — at least that no cur-
rent constantly, or even ordinarily, passes through them.
I have watched them continuously for periods sufficient
to detect such discharge if it were periodic. On one
occasion (viz., that in which the film was protruded like
a blown bladder) a minute Infusorial animalcule chanced
to pass across, close to the surface of the film : this would
have been a decisive test of the existence of a ciliary
current ; but not the slightest deviation in the little
atom's course could be detected.
That the cinclides are the special orifices through
which those missile weapons, the acontia, are shot and
recovered, rests not merely on the probability that arises
from the co-existence of the two series of facts I have
above recorded, but upon actual observation. In a rather
large S. dianthus, somewhat distended, placed in a glass
vessel between my eye and the sun, I saw, with great
distinctness, by the aid of a pocket-lens, many acontia
362 EVENINGS AT THE MICROSCOPE.
protruded from the cinclides, and many more of the latter
widely open. The acontia, in some cases, did not so ac-
curately fill the orifice but that a line of bright light (or
of darkness, according as the sun was exactly opposite
or not) was seen partially bordering the issue of tin-
thread, while the thickened rim of the cinclis surrounded
all.
The appearance of the orifices whence the acontia
issued was that of a tubercle or wart, and the same ap-
pearance I have repeatedly marked in examples observed
on the stage of the microscope ; namely, that of a per-
forate pimple, or short columnar tube. This was clearly
manifest when the animal, slowly swaying to and fro,
brought the sides of the cinclis into partial perspective.
On another occasion I witnessed the actual issue of the
acontia from the cinclides. I was watching, under a low
power of the microscope, a specimen of a S. nivea, while,
by touching its body rudely, I provoked it to emit its
missile filaments. Presently they burst out with force,
not all at once, but some here and there, then more, and
yet more, on the repeated contractions of the corrugating
walls of the body. Occasionally, the free extremity of a
filament would appear, but more frequently the bight of a
bent one ; and very often I saw two, arid even three, issue
from the same cinclis. The successive contractions of the
animal under irritation, caused the acontia already pro-
truded to lengthen with each fresh impetus, the bights
still streaming out in long loops, till perhaps the free end
would be liberated, and it would be a loop no longer ;
and sometimes a new thread would shoot from a cinclis,
whence one or two long ones were stretching already :
while, as often, the new-comers would force open new
cinclides for themselves. The suddenness and explosive
force with which they burst out, appeared to indicate a
resistance which was at length overcome : — perhaps (in
part at least) due to the epithelial film above mentioned,
SEA-ANEMONES I THEIR WEAPONS. 3G-)
or to an actual epiderm,* which, though often ruptured,
lias ever, with the aptitude to heal common to these
lowly structures, the power of quickly uniting again.
It appeared to me manifest, from this and other similar
observations, that no such arrangement exists as that
which I had fancied — that a de6nite cinclis is assigned
to a definite acontium, or pair of acontia ; and that the
extremity of the latter is guided to the former, with un-
erring accuracy, by some internal mechanism, whenever
the exercise of the defensive faculty is desired. What I
judge to be the true state of the case is as follows : The
acontia, fastened by one end to the septa, or the mem-
branes which support them, lie, while at rest, irregularly
coiled up along the narrow interseptal hollows. The
outer walls of these hollows are pierced with the cinclides.
When the animal is irritated, it immediately contracts :
the water contained in the visceral cavity finds vent at
these natural orifices, and the forcible currents carry
with them the acontia, each through that cinclis which
happens to lie nearest to it. The frequency with which
a loop is forced out shows that the issue is the result of
a merely mechanical action ; which is, however, not the
less worthy of admiration because of the simplicity of
the contrivance ; nor the less manifestly the result of
Divine wisdom working to a given end by perfectly
adequate means. The ejected acontia, loaded with their
deadly cniclce in every part of their length, carry abroad
their fatal powers not the less surely than if each had
been provided with a proper tube leading from its free
extremity to the nearest cinclis.
Curious as these contrivances are, there is yet much
more to be told : these are preparatory and ancillary, as
it were, to the elaborate mechanism by which the ultimate
object of the whole provision is to be attained. The
* The outer covering of the external surface of the body, commonly
called the cuticle or scarf-skin.
364
EVENINGS AT THE MICROSCOPE.
ft.
acontium is but a reservoir for the weapons, — a kind of
quiver for the arrows; and the cinclis is a provision for
getting them ready for action : we have not yet looked
at the arrows themselves.
They occur under three principal forms ; and for the
investigation of these we shall find it convenient to have
recourse to different species.
The first and most generally distributed form is the
Chambered Cnida, as it is also the most elaborately
organised. I know of no species in which it can be exa-
mined under so favourable circumstances as the pretty
Madrepore (Caryophyllia Smithii) of our south-western
coasts ; and, as I have several specimens
of that species in my aquarium, subjects are
at hand for our investigation. The clear ten-
tacles are, as you perceive, crowned with
opaque globular heads ; if I should nip off
one of these heads, and flatten it by means
of the compressorium, you would see it
literally composed of cnidce, the ends of
which project side by side, as close as
they can be packed one against another.
But still larger examples may be ob-
tained from the craspeda. With a smart
sudden blow I break the stony skeleton of
the Madrepore in sunder — the flesh tear-
ing apart also ; and thus I expose the
interior of the living animal. A great
number of pellucid ribbons are now seen,
very much convoluted, which are named
craspeda. These are almost composed of
large cnidce.
I remove with fine pliers a small frag-
ment of one of these ribbons, and, placing
it between the plates of the compressorium,
flatten it gradually till the plates are brought
7SR
SA
CNIDA OF
MADEEPOEE.
SEA-ANEMONES : THEIR WEAPONS. 365
into as close contact as they can be. A high power now
being put on, examine the organs in question.
You see a multitude of perfectly transparent, colourless
vesicles, of a lengthened ovate figure, considerably larger
at one end than at the other ; one of average dimensions
measures in length ^^jth of an inch, and in greatest
diameter 2 *0 0th. In the larger (the anterior) moiety,
passing longitudinally through its centre, is seen a slender
chamber, fusiform or lozenge-form, about eVooth of an
inch in its greatest transverse diameter, and tapering to a
point at each extremity. The anterior point merges into
the walls of the cnida at its extremity; while the posterior
end, after having become attenuated like the anterior,
dilates with a funnel-shaped mouth, in which the eye can
clearly see a double infolding of the chamber-wall. After
this double fold the structure proceeds as a very slender
cord, which, passing back towards the anterior end of the
capsule, winds loosely round and round the chamber, with
some regularity at first, but becoming involved in contor-
tions more and more intricate, as it fills up the posterior
moiety of the cavity. The fusiform chamber appears to
be marked on its inner surface with regularly recurring
serrations, which are the optical expression of that
peculiar armour to be described presently.
Under .the stimulus of pressure, when subjected, as
now, to microscopical examination, and doubtless under
nervous stimulus, subject to the control of the will, during
the natural exercise of the animal's functions, — the c?iidce
suddenly emit their contents with great force, in a regular
and prescribed manner. It must not be supposed, how-
ever, that the pressure spoken of is the immediate mecha-
nical cause of the emission : the contact of the glass-plates
of the compressorium is never so absolute as to exert the
least direct force upon the walls of the capsule itself ; but
the disturbance produced by the compression of the sur-
rounding tissues excite3 an irritability, which evidently
3Q6 EVENINGS AT THE MICROSCOPE.
resides in a very high degree in the interior of the cnidcp :
and the projection of the contents is the result of a vital
force.
In general, the eye can scarcely, or not at all, follow
the lightning-like rapidity with which the chamber[and its
twining thread are shot forth from the larger end of the
cnida. But sometimes impediments delay the emission,
or allow it to proceed only in a fitful manner, a minute
])ortion';at a time ; and, sometimes, from the resistance of
friction (as against the glass plate of the compressorium),
the elongation of the thread proceeds evenly, but so slowly
as to be watched with the utmost ease ; and sometimes
the process, which has reached a certain point normally,
becomes from some cause arrested, and the contents of
the cell remain permanently fixed in a transition state.
Thus, a long-continued course of patient observation is
pretty sure to present some fortuitous combinations, and
abnormal conditions, which greatly elucidate phenomena,
that normally seemed to defy investigation.
In watching any particular cnida, the moment of its
emission may be predicted with tolerable accuracy, by
the protrusion of a nipple-shaped wart from the anterior
extremity. This is the base of the thread. The process
of its protrusion is often slow and gradual, until it has
attained a length about equal to twice its own diameter,
when it suddenly yields, and the contents of the cnida dart
forth. At this instant I have, in many instances, heard a
distinct crack or crepitation, both in the examination of
this species and of Sagartia parasitica.
When fully expelled, the thread or wire, which is
distinguished by the term ecthoreum, is often twenty,
thirty, or even forty times the length of the cnida;
though in some species, as in most of the Sagartice, it
frequently will not exceed one-and-a-half or two times
the length of the cnida.
The ecthorea which are discharged by chambered cnida3
SEA-ANEMONES : THEIR WEAPONS.
367
W
are invariably furnished with a peculiar armour. The
l>asal portion, for a length equal to that of the cnida, or
a little more, is distinctly swollen, but at the point indi-
cated it becomes (often abruptly) at-
tenuated, and runs on for the remainder
of its length as an excessively slender
wire of equal diameter throughout. In
the short ecthorea of Sagartia the at-
tenuated portion is obsolete.
It is chiefly upon this ventricose or
swollen basal portion that the elaborate
armour is seen, which is so characteristic
of these remarkable organs. For around
its exterior wind one or more spiral
thickened bands, varying in different
species as to their number, the number
of volutions made by each, and the
angle which the spiral forms with the
axis of the ecthoreum. The whole spiral
formed of these thickened bands is
termed the screw, or strebla.
In the ecthorea emitted by chambered
cnidce from the craspeda of Tealia cras-
s-icornis, the screw is formed of a single
band, having an inclination of 45° to the
axis, and becoming invisible when it has
made seven volutions. In those from
the same organ in &. parasitica, we find
the screw of two equidistant bands,
each of which makes about six turns —
twelve in all — having an inclination of 70° from the
common axis. In those similarly placed in Caryophyllia
Smithii [now under your observation], the strebla is com-
posed, as you may perceive, of three equidistant bands,
each of which makes about ten turns — thirty in all —
with an inclination of about 40° from the axis. In every
CXIDA OF
TEALIA CRASSrCORXIS
(discharged) .
368 EVENINGS AT THE MICROSCOPE.
case the spiral runs from the east towards the north,
supposing the axis to point perpendicularly upwards.
Sometimes, especially after having been expelled for
some time, the wall of the ecthoreumhecomes so attenuated
as to be evanescent, while the strebla is still distinctly
visible. An inexperienced observer would be liable, under
such circumstances, to suppose that the screw, when
formed of a single band, as in T. crassicornis, is itself the
wire ; an error into which I had myself formerly fallen.
An error of another kind I fell into, in supposing that
the triple screw of the wire in C. Smiihii was a series of
overlapping plates : the structure of the weapon is the
same in all cases (with the variations in detail that I have
just indicated) ; and the structure is, I am now well
assured, a spiral thickened band running round the wall
of the ecthoreum on its exterior surface. I have been able,
when examining such large forms as these of Gorynactis
viridis and Caryophyllia Smithii, with a power of 750
diameters, to follow the course of the screw, as it alter-
nately approached and receded from the eye, by altering
the focus of the object-glass, so as to bring each part
successively into the sphere of vision.
These thickened spiral bands afford an insertion for a
series of firm bristles, which appear to have a broad base
and to taper to a point. Their length I cannot deter-
minately indicate, but I have traced it to an extent which
considerably exceeds the diameter of the ecthoreum.
These barbed bristles are denominated pterygia.
The number of pterygia appears to vary within slight
limits. As well as I have been able to make out, there
are but eight in a single volution of the one-banded strebla
in T. crassicornis ; while in the more complex screws of
S. parasitica, Cor. viridis, and Car. Smithii, there appear
to be twelve in each volution.
The barbs, when they first appear, invariably project in
a diagonal direction from the ecthoreum; and sometimes
SEA-ANEMONES I THEIR WEAPONS. 369
they maintain this posture. But more commonly, either
in an instant, or slowly and gradually, they assume a
reverted direction.
From some delicate observations made with a very
good light, I have reason to conclude that the strebla,
and even the pterygia^ are continued on the attenuated
portion of the ecthoreum, perhaps throughout its length.
In Cor. viridis and Car. Smithii, I have succeeded in
tracing them up a considerable distance. In the latter
I saw the continuation of all these bands with their
bristles; but, what was strange, the angle of inclination
had become nearly twice as acute as before, being only
22° from the axis. The appearance of the attenuate
portion, as also of the base of the ventricose part, is
exactly that of a three-sided wire, twisted on itself ; the
barbs projecting from the angles.
The next form of these organs is the Tangled Cnida.
This form is very generally distributed, and is mingled
with the former in the various tissues. In the genus
Sagartia, however, it is by far the rarer form, while in
Actinia and Anthea it seems to be the only one.
The pretty little Corynactis viridis is the best species
that I am acquainted with for studying this kind of cnida- .
A fragment of its craspeda I have here ready for your
observation, prepared exactly like that of C. Smithii.
The figure of the cnidce is nearly that of a perfect oval,
but a little flattened in one aspect, about -^o^h °^ an
inch in the longer, and y^th in the shorter diameter.
Their size, therefore, makes them peculiarly suitable for
observations on the structure and functions of these
curious organs. Within the cavity lies a thread
(ecthoreum) of great length and tenuity, coiled up in
some instances with an approach to regularity, but much
more commonly in loose contortions, like an end of
thread rudely rolled into a bundle with the fingers.
The armour of this kind does not differ essentially
2 B
370
EVENINGS AT THE MICROSCOPE.
from that already described. It is true I have detected
it only in Corynactis, where the short ectkoreum of the
Tangled Cnida is surrounded throughout its length by
a barbed strebla of three bands. The barbs are visible,
under very favourable conditions for observation, even
while the tangled wire remains inclosed in the cnida, but
their optical expression is that of serratures of the walls,
without the least appearance of a screw. This, I say, is
the only species in which I have actually seen the arma-
ture of the ectkoreum in this kind of cnidce ; but I infer
its existence from analogy in other
species, where the conditions that
can be recognised agree with those
in this, though the excessive attenu-
ation of the parts precludes actual
observation of the structure in
question.
Spiral Cnidse constitute the third
form.* In a few species, as Sagartia
parasitica, Tealia crassicor/iis, and
CeriantJms membranaceus, I have
found very elongated fusiform cnida1,
which seem composed of a slender
cylindrical thread, coiled into a very
close and regular spiral. In some
cases the extremities are obtuse, but
in others, as in T. crassicornis, an
example of which I now show you,
the posterior extremity runs off to a
finely-attenuated point, the whole of the spire visible
even to the last ; the whole bearing no small resemblance
to a multispiral shell, such as one of the Cerithiadce or
Twrritelladae. The ecthoreum is discharged reluctantly
from this form, and I have never seen an example in which
* Dr. Karl Mobiiss (Abhandl. Naturw. Yer. z. Hamburg, 1866),
considers this to be only an immature condition. — P. H. G., 1884.
CNIDA OF CORYXACTIS.
sea-anemones: their weapons. 371
the Mrhole had been run off. So exceedingly subtle are
the walls of the cnidce, that it was not until after many
observations that I detected them ; in an example from
T. crassicornis, which had discharged about half of the
wire, I could not see the slightest sign of armature on
the ecthoreum. So far as my investigations go, these
Spiral Cnidse are confined to the walls of the tentacles,
in which, however, they are the dominant form.*
Such, then, are the form and armour of these organs.
But I have not yet done with them. The emission of
the wire, strange to say, is a process of distinct evolution,
or expansion from within, from beginning to end. The
ecthoreum is not a solid, but a tubular, prolongation of
the walls of the cnida, turned-in, in its first condition ,.
like the finger of a glove drawn inwards. Of this fact
you may convince yourself by a careful watching of the
phenomena before you. Many of the ecthorea from the
tangled cnidce now under your eye run out, not in a
direct line, but in a spiral direction. Select one of these,
and you wTill perceive that each bend of the spire is
made, and stereotyped, so to speak, in succession, while
the tips go on lengthening ; the tip alone progresses, the
whole of the portion actually discharged remaining
perfectly fixed ; which could not be on any other
supposition than that of evolution.
In the discharge of the chambered kind (to revert to
those which we were just now examining) we saw the
ventricose basal part first appear ; the lower barbs flew
out before the upper ones, and all were fully expanded
before the attenuated portion began to lengthen. This,
again, is consistent only with the fact of the evolution of
the whole. On several occasions of observation on the
chambered cnidce of C. Smithii, I have actually seen the
unevolved portion of the ecthoreum running out through
* These details, with many others, are given in my Hist, of Brit.
Sea-anemones and Corals, Introd., xxii — xl.
o P o
372 EVENINGS AT THE MICROSCOPE.
the centre of the evolved ventricose portion. But per-
haps the most instructive and convincing example of all
was the following. One of the large tangled cnidce of
Cori/nactis viridis had shot about half of its wire with
rapidity, when a kind of twist, or "kink," occurred
against the nipple of the cnida, whereby the process was
suddenly arrested. The projectile force, however, con-
tinuing, caused the impediment to yield, and minute
portions of the thread flew out piecemeal, by fits and
starts. By turning the stage-screw, I brought the
extremity of the discharged portion into view, and saw
it slowly evolving, a little at a time. Turning back to
the cnida, I saw the kink gradually give way, and the
whole of the tangled wire quickly flew out through the
nipple. I once more moved the stage, following up the
ecthoreum, and presently found the true extremity, and
a large portion of the wire, still inverted ; slowly evolv-
ing, indeed, but very distinct throughout its whole
course, within the walls of the evolved portion.
From all these observations there cannot remain a
doubt of the successive evolution of the entire ecthoreum.
You ask, What is the nature of the force by which the
contained thread is expelled'? That it is a potent force is
obvious to any one who marks the sudden explosive
violence with which the nipple-like end of the cnida
gives way, and the contents burst forth ; as also the ex-
treme rapidity with which, ordinarily, the whole length is
evolved. A curious example of this force once excited
my admiration. The ecthoreum from a cnida of Cory-
nactis viridis was in course of rapid evolution, when the
tip came full against the side of another cnida, already
emptied. The evolution was momentarily arrested, but
the wall of the empty capsule presently was seen to bend
inward and suddenly to give way, the ecthoreum forcing
itself in, and shooting round and round the interior of
the cnida.
sea-anemones: their weapons. 373
The most careful observations have failed to reveal
a lining membrane to the cnida. I have repeatedly
discerned a double outline to the walls themselves, the
optical expression of their diameter ; but have never
detected any, even the least, appearance of any tissue
starting from the walls, as the ecthoreum bursts out. My
first supposition, reluctantly resigned, was, that some
such lining membrane, of high contractile power, lessened,
on irritation, the volume of the cavity, and forced out
the wire.
The cnida is filled, however, with a fluid. This is
very distinctly seen occupying the cavity, when, from any
impediment, such as above described, the wire flies out
fitfully ; waves, and similar motions, passing from wall
to wall. Sometimes, even before any portion of the wire
has escaped, the whole mass of tangled coils is seen to
move irregularly from side to side, within the capsule,
from the operation of some intestine cause. The emission
itself is a process of injection ; for I have many times
seen floating atoms driven forcibly along the interior of
the ecthoreum^ sometimes swiftly, and sometimes more
deliberately. Nothing that I have seen would lead me
to conclude that the wall of the cnida is ciliated.
I consider, then, that this fluid, holding organic
corpuscles in suspension, is endowed with a high degree
of expansibility ; that, in the state of repose, it is in a
condition of compression, by the inversion of the ectlio-
reum; and that, on the excitement of a suitable stimulus,
it forcibly exerts its expansile power, distending, and, con-
sequently, projecting, the tubular ecthoreum, — the only
part of the wall that will yield without actual rupture.
It has been proved that the execution of these weapons
is as effectual as their mechanism is elaborate. The wire
shot with such force penetrates even to its base the tissues
of the living animals which the Anemone attacks ; and
then its barbs preclude the withdrawal of the dart. But
374 EVENINGS AT THE MICROSCOPE.
the entrance of bodies so excessively slender would of
itself inflict little injury; there is evidently the infusion
at the same time of a highly subtle poison into the wound ;
some venomous fluid escaping with the discharge of the
ecthoreum, which has the power, at least when augmented
by the simultaneous insertion of scores, or hundreds, of
the weapons, of suddenly arresting animal vigour and
speedily destroying life, even in creatures — fishes, for
example — far higher than the Zoophyte in the scale of
organisation. I have seen a little fish in perfect health
come into accidental contact with one of the acontia of
an irritated Sagartia, when all the evidences of distress
and agony were instantly manifested ; the little creature
darted wildly to and fro, turned over, sank upon the
bottom, struggled, flurried, and was dead.
Admitting the existence of a venomous fluid, it is diffi-
cult to imagine where it is lodged, and how it is injected.
The first thought that occurs to one's mind is, that it is
the organic fluid which we have seen to fill the cnida, and
to be forced through the everting tubular ecthoreum. Bu t
if so, it cannot be ejected through the extremity of the
ncthoreum, because if this were an open tube, I do not see
how the contraction of the fluid in the cnida could force it
to evolve ; the fluid would escape through the still inverted
tube. It is j ust possible that the barbs may be tubes opei 1
at the tips, and that the poison-fluid may be ejected
through these. But I rather incline to the hypothesis,
that the cavity of the ecthoreum, in its primal inverted
condition, while it yet remains coiled up in the cnida, is
occupied with the potent fluid in question, and that it
is poured out gradually within the tissues of the victim,
as the evolving tip of the wire penetrates farther and
farther into the wound.
I do not think that the whole range of organic exist-
ence affords a more wonderful example than this of the
minute workmanship and elaboration of the parts ; the
SEA- ANEMONES : THEIR WEAPONS. 37">
extraordinary modes in which certain prescribed ends are
attained, and the perfect adaptation of the contrivance to
the work which it has to do. We must remember that
all this complexity is found in an animal which it is
customary to consider as of a very simple structure. But
the ways of God are past finding out. These are but
parts of His ways.*
* The presence of these very remarkable organs is not limited to the
Actinoids. They exist in the entire class of Polyps, including the
Medusa?, also in the Synaptic (see p. 299 svpra), many Turbellarice,
some of the Annelids, and a few among the Mollusca. Dr. R. Bergh of
Copenhagen has published (1861) some elaborate researches, proving
the existence of urticating cnidse, in abundance, in several forms of
the charming Naked-gilled Mollusca, allied to Eolis ; while they seem
to be wanting in the tougher-skinned Doris, &c.
376 EVENINGS AT THE MICROSCOPE.
CHAPTER XX.
PROTOZOA AND SPONGES.
We are so accustomed to see certain of the vital functions
of animals performed by special organs or tissues, that we
wonder when we find creatures which move without limbs,
contract without muscles, respire without lungs or gills,
and digest without a stomach or intestines. But thus we
are taught that the function is independent of the organ,
and, as it were, prior to it ; though in nine hundred and
ninety-nine cases out of a thousand it be associated with
it. In truth, the simplest forms of animal life display
very little of that division of labour, the minuteness of
which increases as we ascend the organic scale ; the
common tissue is not yet differentiated* (to use the
awkward term which is becoming fashionable among phy-
siologists) into organs, but it is endowed with the power
of fulfilling various oifices, and performing many functions.
In all probability, the function is but imperfectly per-
formed; the specialisation of certain tissues, and their
union into organs, and the complexity of such combina-
tions, no doubt, perform the given function in a far more
complete degree; and it is the number and elaborateness of
these that constitute one animal higher in the scale than
another. The human lung is no doubt a more complete
breathing apparatus than the entire ciliated surface of an
Infusory,f and the human eye sees more perfectly than
* The term is used to express the cellular development of an organi-
sation from its original germ.
+ The name given to a class of minute animals from their being
generally developed in infusions of animal or vegetable matter.
PROTOZOA AND SPONGES. 377
the loose aggregation of pigment granules on the edge of
a Medusa. But this diversity is essential to creation,
as the great and wondrous plan which we see it to be ;
and, meanwhile, we may rest satisfied that the humble
requirements of the lowest organism are met adequately
by its humble endowments.
This evening I propose to show you some of these
humble conditions of animal life ; the lowest of the
lowly. I have here two or three phials of very rich
water from the fresh-water ponds in the neighbour-
hood. All collections of water are not equally pro-
ductive; and very far indeed is the popular notion
from correctness, that every drop of water which we
drink contains millions of animalcules. You may
find many collections of clear water, springs, streams,
and pools, from which you may examine drop after drop
in succession, with the highest powers of the microscope,
and scarcely discover a solitary animalcule. Again, it
is not stagnant and fetid pools that are the richest in
vitality ; though no doubt you will always obtain some
forms abundantly enough in such conditions. Accord-
ing to my own experience — an experience of many years
— the paucity or profusion of animal life in any given
collection of water can never be determined beforehand ;
the season, the situation, the aspect, the character of the
country, and many other ud suspected conditions, in-
fluence the result, at which yet one may often give a
shrewd guess. Generally speaking, small ponds, in which
there is a good deal of vegetation below the surface,
and particularly if this be of a minutely divided cha-
racter, such as Myriophyllum, Char a, &c, and whose
surface is well covered with duckweed (Lemna), yield
well ; and, in collecting, it is desirable so to dip that
some of the fine loose sediment of the bottom may flow
into your phial, and then to pluck up one or more of
the filamentous water-plants, and introduce these into it.
378 EVENINGS AT THE MICROSCOPE.
Now to examine such a collection, proceed as I am about
to show you. Hastily glancing with the pocket-lens over
the foliage, and selecting such filaments as seem the most
loaded with dirty floccose matter, I pluck off with pliers
one or two, together with one or two of the cleaner ones
that are higher up on the plant, nearer the growing point.
Having laid these on the lower glass of the live-box, I
take up with the tip of a fine tube, or a pipette, a minute
quantity of the water at the bottom, which flows in as you
see, carrying a few granules of the sediment. This drop I
discharge upon the glass of the live-box, put on the cover,
and place the whole on the stage of the microscope.
First, let us use a low power, one hundred diameters
or so, in order to take a general glance at what we have
got. Here is an array of life, indeed ! Motion arrests
the eye everywhere. " The glittering swift and the flabby
slow" are alike here; clear crystal globules revolve giddily
on their axes ; tiny points leap hither and thither like
nimble fleas ; long forms are twisting to and fro ; busy
little creatures are regularly quartering the hunting-
ground, grubbing with an earnest devotedness amoncr the
sediment as they march up the stems; here are vases with
translucent bodies protruding from the mouths; here are
beauteous bells, set at the end of tall threads, ever
lengthening and shortening ; here are maelstroms in
miniature, and tempests in far less than a teapot ; rival
and conflicting currents are whirling round and round,
and making a series of concentric circles among the
granules. Surely here is material for our study.
I see an object slowly creeping along the glass, which
will be just the thing for our purpose. It is the Proteus
{Amoeba diffluens)* Let me put on a higher power, and
submit it to your observation.
* The names given to this little creature are expressive of its charac-
ter. Amoeba is from the Greek a/ictj3t) (amoibe), signifying change ; and
Proteus in mythology was an old prophet of the sea, who when seized
assumed all manner of forms to avoid uttering his predictions.
PROTOZOA AND SPONGES.
379
You see a flat area of clear jelly, of very irregular form,
with sinuosities and jutting points, like the outline of some
island in a map. A great number of minute blackish
granules and vesicles occupy the central part, but the
edges are clear and colourless. A large bladder is seen
near one side, which appears filled with a subtle fluid.
But while you gaze on it, you perceive that its form is
changing : that it is not at two successive moments of
exactly the same shape. This individual, which when you
first looked at it was not unlike England in outline, is
now, though only a few minutes have passed, something
totally different; the projecting angle that represented
Cornwall is become rounded and more perpendicular;
the broken corner that we might have called Kent has
formed two little points up in the position of Lincolnshire;
the large bladder, which was in the place of the Eastern
counties, is moved up to the Durham coast, and is,
moreover, greatly diminished ; and other like changes
have taken place in other parts.
Lo ! even while speaking of these alterations, they have
been proceeding, so that another and a totally diverse out-
FOKMS OF AMCEBA.
Successively drawn from one individual .
line is now presented. A great excavation takes the place
of Dorset ; Kent is immensely prolonged ; the bladder
has quite disappeared, &0.; but it is impossible to follow
these changes, which are ever going on without a moment's
380 EVENINGS AT THE MICROSCOPE.
intermission, and without the slightest recognisable rule or
order. The projections are obliterated or exaggerated ;
the sinuosities are smoothed, or deepened into gulfs, or
protruded into promontories ; firths form here, capes
there; but not by starts, but evenly, and with sufficient
rapidity to be appreciable to the eye while under actual
observation; though the alterations are more striking if
you take your eye off the object for a few seconds, and
then look again ; and still more so if you try to sketch
the outline. Individuals vary greatly in dimensions; this
specimen is about one hundred and twentieth of an inch
in long diameter, but others I have seen not more than
one-tenth as large as this, and some twice as large.
Disregarding now this peculiarity of change of form,
which has procured for it the name of the old sea-god that
was so difficult to bind, we will concentrate our attention
on some other points not less interesting. That great
bladder undergoes changes besides those gradual altera-
tions of place which are dependent on the general form.
It slowly but manifestly increases in size up to a certain
extent, when it rather suddenly diminishes to a point, and
immediately begins to fill again, as slowly as before.
These alternations go on with some regularity, and we
cannot observe them without becoming convinced that it
is a process of filling and emptying; that the bladder
gradually fills with a fluid which is either secreted by its
walls or percolates into it from the surrounding tissue ;
which fluid, when full, the bladder discharges by a sudden
contraction of its outline. But whither the fluid goes it is
difficult to determine ; I have never been able, in this or
in any other instance of its occurrence (though this con-
tractile bladder is characteristic of the extensive classes
Infusoria and Rotifera) to see any issue of fluid from the
bodyatthe moment of contraction; and therefore conclude
that it is discharged into the body, perhaps back again
into the tissues from whence it was taken up, and from
PROTOZOA AXD SPONGES. 381
whence it was about to be collected again. Hence it is
probably the first obscure rudiment of a circulation ; the
lluids impregnated with the products of digestion being
thus collected, and then diffused throughout the soft and
yielding tissues.
The smaller bladder-like spaces that you see in con-
siderable numbers in the substance of the animal, are
collections of fluid contained in excavations of that sub-
stance, which are called vacuoles, differing from vesicles,
inasmuch as they seem to have no proper wall or inclosing
membrane, but to be merely casual separations of the
common substance, such as would be made by drops of
water in oil. These vacuoles appear to be connected
with the digestive function ; for very many of them are
not clear, but are occupied with granules more or less
opaque, and of exceedingly various dimensions. That
these collections of granules are food you will see by the
following experiment.
I mingle a little carmine with the water, just enough to
impart a visible tinge to it, and close the live-box again.
Already you perceive that some of the tiny globules are
become turbid and red, and that their opacity and colour
are deepening perceptibly. We see by this that the par-
ticles of carmine have been taken into the jelly-like sar-
code, and are accumulating in little pellets surrounded
by fluids, in these casual hollows of its substance. The
process is rendered still more obvious when, as is often
the case, some Diatomacean,* with a hard siliceous shell,
becomes the food of the Amoeba. The apparently helpless
jelly spreads itself over the organism, so as soon to envelop
it; the flesh, which, having no skin, can unite with itself
whenever the parts come into contact, closes over the
* The Diatomacece, a term formed from the Greek cia (dia), through,
and rkfivtiv (temneio), to cut, are so called from the ease with which
their masses may be broken or cut through ; whence their popular
name of brittle-worts. They are usually considered to belong to the
vegetable kingdom.
382 EVENINGS AT THE MICROSCOPE.
Diatom, which is thus brought into the midst of the
sarcode, a vacuole being new-made for its reception.
This, then, performs the part of a temporary stomach :
the digestible portions of the prey are extracted, and then
the insoluble shell of flint is, as it were, gradually squeezed
to some part of the exterior, and gradually forced out,
the vacuole disappearing with it, or perhaps retaining a
minute portion of the fluid, and thus perpetuating itself
for a while. This is the earliest condition in which the
process of digestion can be recognised.
Another genus somewhat similar is Arcella, but it differs
in being furnished with a more or less rounded shell
(lorica), like a little box. In examining the matters that
adhere to the stems of duckweed, and other water-plants,
we frequently observe little circular bodies of a yellowish
or reddish-brown colour, some much darker than others,
but all having a central round spot paler than the rest.
On first examination they seem inert and dead, but if we
closely watch one, we perceive that it is endowed with the
power of motion ; and we directly discern, thrust out from
its edge, variable processes, in the form of arms, of clear,
perfectly colourless, and most delicate jelly, sometimes
pointed, sometimes blunt, which slowly change their form
and position. By the aid of these, a feeble and irregular
motion is given to the box, which is sometimes turned
partly over; when we perceive that its under side is flat,
or probably concave, and that its outline is cut into facets.
The lorica is somewhat flexible, for the edges at two
opposite points are sometimes bent down towards each
other, so as to give the creature the form of a crescent.
The internal viscera are dimly discernible through the
coloured lorica, and resemble those of Amoeba. A dark
oval ring is commonly seen at one side, which is probably
the outline of the contractile bladder. It may, in fact, be
considered as an Amoeba, whose external surface has the
power of secreting a symmetrical shell of horny or
PHOTOZOA AND SPONGES. 383
chitinous substance. The lorica is about T* ^th of an inch
in diameter. This species is named Arcella vulgaris.
Laying aside our live-box with its contents for the
present, we will have recourse to the tanks of sea-water
for one or two other objects of intermediate interest. On
the green and brown mossy sea-weed which covers the
rocks on the bottom, you see many white specks clinging
to the filaments; and there are several adhering to the
sides of the tank. These are little living shelled animals
of the class Iforaminifera, and these which you see include
several species. By bringing your eye, assisted by the
lens, to bear upon one of these latter, you perceive that
it is a little discoid spiral shell, of very elegant form,
marked with curved diverging grooves. This is the pretty
little Pobjstomella crispa, a fair sample of its class, and
though not more than -g^th of an inch in diameter, it is
a giant compared with the Arcella.
There is more, however, than the shell to be seen ;
though so filmy and shadowy, that I wonder not at your
overlooking it. Extending from two opposite sides of the
shell to a distance each way considerably exceeding its
diameter, you discern fine threads of clear jelly, running
out in long points. The power you employ is not suffi-
cient to enable you to resolve their detail : and for this
I will try to secure a specimen for the microscope.
In this other live-box, then, I inclose one of the white
specks from the moss-like clothing of the stones. It is,
I see, of another species, namely, Pohjmorphina oblonga;
but it will answer our purpose equally well.
At present we see only the shell, the removal of the
animal having induced it in alarm to withdraw the whole
of its softer parts within the protection of its castle. We
must have a few minutes' patience.
Now look again. From the sides of the opaque shell
we see protruding tiny points of the clear sarcode; these
gradually and slowly, — so gradually and slowly that the
384 EVENINGS AT THE MICROSCOPE.
eye cannot recognise the process of extension — stretch
and extend their lines and films of delicate jelly, till at
length they have stretched right across the field of view.
The extension is principally in two opposite directions,
corresponding to the long axis of the shell; though the
branched and variously connected films often diverge
considerably to either side of these lines, giving to the
whole a more or less fan-shaped figure.
These films are as irregular in their forms and sizes as
the expansion of the sarcocle of Amoeba, with which they
have the closest affinity. Their only peculiarity is their
tendency to run out into long ribbons or attenuated
threads, which, however, coalesce and unite whenever
they come into mutual contact, and thus we see the
threads branching and anastomosing with the utmost
irregularity, usually with broad triangular films at the
points of divergence and union.
There can be no doubt that the object of these length-
ened films, which are termed psevAopodia* is the capture
of prey or food of some kind ; perhaps the more sluggish
forms of minute animalcules, or the simpler plants. These
the films of sarcode probably entangle, surround, and
drag into the chambers of the shell, digesting their softer
parts in temporary vacuoles, and then casting out the
more solid remains, just as the Amoeba does.
Though this beautiful array was so very deliberately
put forth, it is, as you perceive, very rapidly withdrawn
on any disturbance to the animal, as when we agitate the
water by slightly moving or turning the cover of the live-
box. Another fact, of which you may convince yourself,
by watching manifest, though small, changes of position
in the shell, while under observation, is, that it is by
means of the adhesion and contraction of the jiseitdopodia,
that the animal drags itself along a fixed surface. This
* Literally, false feet, from the Greek iptudog (pseudos), a falsehood,
and ttovq (pous), genitive 7rodoQ (podos), afoot.
PROTOZOA AND SPONGES. 385
it can effect so assiduously, that I frequently find them
in the morning adhering to the tank-sides three or four
inches from the bottom, though, on the previous evening,
none were visible on the glass. Thus they must crawl,
on occasion, from a hundred to a hundred and fifty times
their own diameter in a night.
The structure of a Sponge is much the same as that
of these animals, with the exception that its solid part or
skeleton is not a continuous covering by which the sarcode
is invested, but consists of fibres or points or rods of vary-
ing form, which are clothed with the sarcode. This loose
sort of skeleton may be of horny or chitinous matter, like
that of Arcella, or calcareous like that of the Foraminiferdt*
or it may be siliceous, — that is, composed of flint (silex).
In some cases, as in the common Turkey Sponge, the
horny skeleton consists of a network of solid but slender
fibres, very tough and elastic, which branch and anasto-
mose in every direction, at very short intervals, as you
may see by looking at this atom, which 1 cut off from a
dressing-sponge.
In the lime and flint Sponges, however, the continuity
and cohesion of the skeleton does not depend upon the
organic union of the constituent parts, as it does in the
loose and open network of the Turkey sponge. For it is
made up of an immense multitude of glassy needles, all
separate and independent, between themselves, yet so con-
trived that they do hold together very firmly, and in a
great number of cases are arranged on a prescribed plan,
so as to give a certain form and outline to the aggregate.
If you have ever shaken up a box of dressing-pins, and
have then endeavoured to take one out, you know how by
their mere interlacement they adhere together in a mass,
* A group of animals with shells, resembling in appearance those of
the common nautilus ; and, like them, consisting of several chambers
divided from one another by walls which are pierced with numerous
minute holes, in Latin called foramina; — whence their name.
2 c
386
EVENINGS AT THE MICROSCOPE.
so that by taking hold of one you may lift a bristling group
of scores. Somewhat on the same principle are the cal-
careous and siliceous pins (spicula) of a Sponge held
together by mutual interlacement. Yet their cohesion is
aided by the tenacity of the living sarcode which invests
them ; for I have found that specimens of Grantia (cal-
careous Sponges with needles of three rays), when long
macerated in water, so that the sarcode is dissolved, have
very slight power of cohesion among their spicula.
To understand the structure of a sponge we will shave
a thin sectional slice from this Halichondria suberea.
This when alive is of an orange colour ; and is always
found closely investing turbinate, or top-shaped, shells
which are inhabited by Hermit-crabs. We will macerate
the slice in tepid water for a quarter of an hour, and
then examine it in the live-box.
The surface is a thin layer of greater density than any
other part, and is composed of coloured fleshy granules, —
SECTION OF SPONGE.
omitting for the present, the skeleton. Of the same sub-
stance is the whole slice composed, but looser and more
open as it recedes from the surface. It is separated by
PROTOZOA AND SPONGES. 387
blank spaces which are larger towards the centre, smaller
and more numerous as they approach the exterior.
These openings are sections of so many canals, by
which the whole substance of a sponge is permeated.
The surface is perforated with minute pores, at which the
surrounding w^ater enters on all sides. These presently
unite into slender pipes, which, irregularly meandering,
are continually uniting into larger and yet larger canals ;
of wThich the greater open spaces that you see are the
oblique divisions. These have certain outlets, called
oscula, on the surface, from which the stream is poured
that has thus made the grand tour of the whole interior.
Such oscula, as you perceive on the remainder of the
Halichondria, are usually raised on slight eminences ;
and resemble, especially when in living action, miniature
volcanoes, vomiting torrents of water and granules of
effete matter, instead of fire and ashes.
During life these granules were much more diffused,
and formed a considerable portion of the living flesh,
the remainder being composed of a glairy sarcode, almost
fluid. The whole was maintained in position by the
solid spicula of flint, which you see abundantly in this
slice. These take a curious form, exactly that of the
pins which wTe use on our dressing-tables ; each consist-
ing of a cylindrical slender rod, pointed at one end,
and at the other surmounted by a globular head, the
whole formed of glass, — -flint glass literally. You see
them bristling all round the edge of the section, being
stuck into the surface of the sponge, exactly as pins are
loosely stuck into a pin-cushion. The heads and points,
too, project into the cavities; more, however, than they
did during life, for you must make allowance for the
shrinking of the soft parts ; and thus you perceive how
the whole structure is permeated by these glassy pins,
Avhich seem to be entangled together quite at random
without rule or arrangement. And yet there is an
2 c 2
o o
88 EVENINGS AT THE MICROSCOPE.
arrangement discernible here ; for the canals are formed
by the manner in which these are grouped ; and this is
seen much more clearly in the case of the three-rayed
needles of lime in the Grantice. Mr. Bowerbank has
shown that in G. compressa the substance is divided
into very regular chambers in a double series, divided
by a diaphragm, whose axis is at right angles to the
axis of the sponge ; and that these chambers are denned
by walls made up of the three-rayed needles in their
mutual interlacement.
INFUSORIA. 389
CHAPTER XXT.
INFUSORIA.
We will now resume our examination of the drop of
pond-water, and the fragments of Myriophyllum, which
have been waiting for us in the live-box.
Our attention then shall first be given to some elegant
creatures of a brilliant translucent green hue, which are
gracefully gliding about. They are of the genus Euglena,
so called because each is furnished with a very conspicu-
ous spot of a clear red hue, situated near the head, which
Ehrenberg, on account of its resemblance to the lowest
forms of eyes in the Rotifera, that are somewhat similar
in colour and appearance, pronounced to be an organ of
vision. More recent physiologists, however, doubt the
correctness of the conclusion.
The animals are of several kinds. The most numerous
is an active little thing of about T^ of an inch in
length when extended, though from its extreme versa-
tility it is as difficult to assign to it a definite size as a
definite shape. It seems to be the E. sanguinea, so called
because it is said to occur sometimes of a deep red huey
and in such vast profusion as to give the waters the
appearance of blood. I have never seen it, however,
other than as it now appears, rich emerald green in the
body, with the two extremities perfectly clear and
colourless. I might, perhaps, describe its ordinary form
as spindle-shaped, with a pointed tail, and a blunt,
rounded head ; but it is remarkable for the variableness
of its shape. It is capable of assuming an appearance
390 EVENINGS AT THE MICROSCOPE.
very diverse from what it had half a minute before, so
that you would hardly identify it, if you were not watch-
ing its evolutions. Whether this ability to prove an
alias be at all dependent on the remarkable clear-headed-
ness of the subject, I leave for those who are skilled in
metaphysics to determine. Away they go, tumbling-
over and over, revolving on the long axis as they
proceed, which they do not very rapidly, with the blunt
extremity forward.
Here is another kind, a little larger than the former,
but much more slender; yet from the slowness and steadi-
ness of its movement more easy of observation. It is
named E. acus, or "the Needle Euglena." This is an
animalcule of great elegance and brilliancy ; its sparkling
green hue, with colourless extremities, and its rich pale
crimson eye, are very beautiful. It commonly swims
extended, with a slow gliding motion, turning round on
its long axis as it proceeds, as may be distinctly seen by
the rotation of certain clear oblong substances in its body.
These, then, are seen not in the interior, but near the
surface, as they would appear if imbedded in the flesh
around a hollow centre. The interior is probably not
hollow, but occupied with pellucid sarcode. These were
assumed by Ehrenberg, but on no adequate grounds, to
be organs connected with reproduction. They vary in
number in different individuals, and those which contain
the greatest number are thereby more swollen. They
appear to be separated into two series, one anterior, the
other posterior. The animal is capable of bending its
head and body in various directions, but is most beautiful
when straight. The front is furnished with a slender
thread-like proboscis. This species affords us a good
opportunity of observing the red spot, which, for con-
venience sake, we may still term an eye. It seems to be
an irregular oblong vacuole, or excavation in the sarcode,
tilled with a clear ruby-red fluid. The red spot in the
IXFL'SORIA.
.391
Rotifera is connected with a well-defined crystalline lens,
whose definite form and high refractive power may in
many cases be distinctly marked ; but here nothing of
the kind is seen ; the spot itself has no certain shape,
and does not appear to be bounded by a proper wall.
Some forms, which are by general consent admitted to
be plants, have similar spots ; and hence it has been,
rather too hastily, I venture to think, concluded that
they have no connexion with vision. I think it still
possible that a sensibility to the difference between light
and darkness may be the function of the organ.
I have found that this animal, when allowed to dry
on a plate of glass, retains its form and colour perfectly ;
but in about two days the eye-spot, which at first be-
comes much larger in the drying, gradually loses all
traces of its brilliant colour, probably by the evapora-
tion of the contained fluid.
Another pretty species you see gliding along among
the rest, called E. triqrietra, or the Three-sided. It bears
a resemblance to a broad rounded leaf, with the foot-
stalk forming a short transparent point, and the mid-rib
elevated into a sharp ridge. The
under side seams slightly con-
cave. This is equally attractive
with the others. It is persistent
in form, and appears not to be
even flexible. Its motion is slow,
and as it goes it rolls irregularly
over and over in all directions,
not revolving on its long axis,
and thus giving you very satisfactory views, though only
momentary, of the keel with which the back is furnished.
It is in the turnings of such minute creatures that the
microscopist often gets a glimpse of peculiarities of form,
which a view of the animal when in repose, however long
continued, fails to reveal. Longitudinal interrupted lines
THBEE-SIDED EVGLENA.
392 EVENINGS AT THE MICROSCOPE.
are seen running down the body of this pretty leaf, which
do not appear to mark irregularities of the surface, and
therefore are probably internal. Ehrenberg calls these
and similar collections of granules " ova," or eggs ; but
this is to cut the knot instead of untying it. There is
no sufficient reason to believe that these animals increase
by ova.
About the front of all these Euglence, you may discern
now and then a slight nickering or quivering in the water.
The power we are using, though best for the general
display of the form, is insufficient to resolve this appear-
ance : I will put on a higher objective. You now see
that there proceeds from the frontal part of the body a
long and very slender filament, which is whisked about
in the manner of a whip-lash. This is considered to be
the organ of locomotion ; but I rather doubt that such
is the function ; the smooth and even gliding, often ro-
tating, action of the creature, seems more like that pro-
duced by minute and generally-distributed cilia, than
that caused by the lashings of a single long thread.
Yet two more species of this extensive genus we dis-
cern in this well-stocked drop of water. They have
received the appellations of the Pear (E. pyrum) and the
Sloth (E. deses). The former is the most minute we have
yet seen and seems to be scarce ; but it is highly curious
and interesting in appearance. It much resembles in
outline a fish of the genus Balistes ; the muzzle being
somewhat protruded and truncate, and the form rhom-
boidal ; it terminates in a slender pointed tail. The body
is obliquely fluted, which gives a very singular effect ;
for, from the transparency of the tissues, the lines of the
opposite side can be discerned crossing those next the
eye, and dividing the animal into lozenge-shaped areas.
The colour is sparkling green, but the tail and the edges
of the body are clear and colourless, and there is a bright
red eye. At other times this Euglena takes the form of a
INFUSORIA. 393-
claret-bottle or an oil-flask ; the muzzle being broadly
truncate or even indented.
Its motion is rapid ; a swift gliding in the direction
of its long axis : it turns continually on the same axis,
which gives a waving irregularity to its course, and has
a pretty effect from the continual crossing of the flutings
in the revolving. This specimen is about T^ of an
inch in length, including the tail.
Euglena deses is much larger, being about ~jj of an
inch in length, though the tail is very short. It has a
thick body, with a round, blunt head ; it tapers suddenly
to the tail. Its colour is bright green with a red eye;
but the presence of an infinite number of irregular ob-
long granules and lines with several globular vesicles,
gives an opacity and a blackness to its appearance. In
its manners it is sluggish ; it never swims or glides
gracefully and swiftly among its playful companions,
but contents itself with twining slowly among the downy
stems and filaments of the water-plants, or crawls upon
the surface of the live-box. It does not appear to change
its form, otherwise than its soft and flexible body neces-
sitates, as it twines about.
But enough of the Euglence. For I have just caught
sight of a much more curious creature, the Swan Ani-
malcule (Trachelocerca olor). It is reposing on one of
the leaves of the MyriophyMum, its long and flexible
neck lengthening and contracting at pleasure, the tip
thrown about in quick jerks in every direction, some-
what like a caterpillar when it touches several points
impatiently with its head.
If we admire the graceful sailing of a swan upon a
lake, the swelling of its rounded bosom, the elegant
curves of its long neck, we shall be struck with the form
and motion of this animal. The form has much resem-
blance to that of a swan, or still more to that of a snake-
bird (PloHut) ; the body, swelling in the middle, tapers
394
EVENINGS AT THE MICROSCOPE.
gradually into a slender pointed tail at one extremity,
and at the other into a very long and equally slender neck,
which is terminated by a slight dilatation. The whole
is perfectly transparent, but the body is filled with nume-
rous minute globular vessels, or temporary stomachs.
The grace of its motion, as it glides along with a free
and moderately swift progression through the clear
water, or winds through the intricate passages of the
green conferva, throwing its long neck into elegant
curves, is very remarkable. There are, I see, two of
them, which, however, take no notice of each other,
even when passing close to each other ; the neck of one
SWAN-NECK AND ITS DIVISIONS.
is much longer than that of the other. Now and then,
when gliding along, the neck is suddenly contracted, but
not wholly, as if something had alarmed or displeased
the animal ; the body also can be swollen or lengthened
at pleasure ; it can move in either direction, but the
neck usually goes foremost, extended in the direction of
the motion, and seems to be used to explore the way.
I had once an opportunity of seeing the process of in-
crease by spontaneous self-division in this creature. It
was an unusually large specimen, found in an old infusion
of sage leaves. When I discovered it, it was darting
about its long neck in the most beautiful contortions.
As it was partly hidden by the vegetable fibre present, I
INFUSORIA. 395
turned the glass cover so as to alter the position of the
contents. On again looking, the Swan was in a clear part
of the field, but in the form of a dark globose mass, the
neck being entirely contracted. It was quite still, except
a continual slight alteration of the form by the protrusion
or contraction of parts of the outline. The body seemed
full of minute globules, .set in a granular mass of a
blackish hue, and the outline was not a continuous line,
but formed a multitude of rounded elevations. Presently
it protruded the clear neck, but only for a short distance,
and then retracted it as before ; when the only indication
of the presence of this organ was a depression in one
part of the surface, somewhat like the mouth of a closed
Actinia, where there was a slight but incessant working,
very much like the irregular motion on the surface of
boiling water, in miniature; there was also an indistinct
ciliary action at this part, not of rotation, nor of vibration,
but a sort of waving. At this point I had occasion to get
up from the table, and though I was not away more than
a minute, on my return I observed a strong constriction
around the middle of the bodv. It was transverse, for
the depressed and ciliated mouth was at a point exactly at
right angles to the constriction. From the depth to which
this latter extended in so few minutes, I supposed the
process of separation would be very rapid ; for I could
very soon see a line of light all across at intervals, and
the two halves seemed to slide freely on each other. Yet
they remained long without much apparent progress, or
even change, except that the anterior half at one time
threw forth its neck a short distance ; at this time it
looked extremely like a bird, bridling up its lithe neck and
swelling bosom; while, to make the resemblance perfect,
it began to imitate the action of a fowl picking up grain,
bobbing its head hither and thither : so curious are the
analogies of nature ! Along the dividing line there had
appeared very early in the posterior half a distinct ciliary
396 EVENINGS AT THE MICROSCOPE.
action; after a while (how, I do not exactly know), with-
out the general relation of position being changed, the
mouth of the anterior (which must now be called the old)
animal appeared on the side, and at the point corre-
spondent in the other, a similar ciliary wreath appeared,
while the action along the dividing line was no longer
seen. So that the division which was at first transverse
now appeared longitudinal. I believe, however, the
animals were really separated before this, though they
remained in contact, for as they slid over each other it
was manifest that each had an independent action.
At length, about an hour and a half after the first
appearance of the constriction, the new animal threw out
its clear neck to a great length, writhing it about with
rapid agility, and forming the most elegant curves, like
those of a serpent, often completely encircling its own
body with it. It still remained, however, in contact with
its parent, which after a time also protruded its neck in
the same manner. Both then retracted and remained still
for a while; and again, almost simultaneously threw out
their long necks and then retired to sluggish repose.
Among the sediment, the grains of which are driven
hither and thither by their spasmodic, jerking movements,
you see several individuals of another sort of creature, —
the Chrysalis Animalcule (Paramcecium aurelia). This
is a "Triton among minnows"; for it is greatly larger
than any of those we have yet observed, and is just
visible to the naked eye, when we hold up the live-box
obliquely against the light ; for then the animals appear
as the smallest possible white specks.
Bringing them again under the microscope, each pre-
sents a pellucid appearance, and an oblong figure, of which
the fore part is somewhat narrowed. The back rises in a
rounded elevation, and the mouth is situated as far back
as the middle of the body upon the under surface, where
its position is marked by a sort of long fold, the sides of
INFUSORIA. 397
which are fringed with long cilia, whose vibrations are
very marked. The whole surface, on both sides, is
covered with minute cilia, arranged in longitudinal rows,
of which, according to the great Prussian professor, there
are from thirty to sixty on each surface, each row bearing
sixty or seventy cilia. This must be considered as an
approximation ; for we may well doubt the accuracy of
the counting, when the objects are so very evanescent as
these vibrating cilia.
The vacuoles, and the temporary stomachs, more or less
completely tilled with the brown and green food, which the
animals are collecting from the decayed vegetable matters,
are sufficiently numerous and conspicuous ; but they may
be rendered still more so by the device of mixing a little
carmine with the water. The ciliary currents are thus
instantaneously rendered strikingly visible. The crimson
atoms are attracted from all quarters towards the tail of
the animal, whence they are urged in a rapid stream along
one side towards the head, around which they are hurled,
and then down the other side to the tail, pouring off in
a dense cloud in a direction contrary to that in which
they originally approached.
But now the gathered currents have produced their
expected result ; for many of the globular vacuoles are
already become of a beautiful rosy hue, from the minute
particles of the pigment which have been whirled to the
mouth, and swallowed.
The feature of greatest interest, however, in this
animal is the contractile bladder. Two of these organs
are usually seen co-existent in each individual, placed,
the one on the front, the other in the rear of the mouth,
but near the opposite, — i.e., the dorsal, — surface of the
body; for as the creature slowly revolves on its longitu-
dinal axis, the line of the vesicles alternately approaches
and recedes from that of the mouth. They are remarkable
for their structure. Far from the simplicity in which the
398 EVENINGS AT THE MICROSCOPE.
organ is usually presented to us in the animals of this
class, the contractile bladders are here very complex.
Each when distended is globular; and it is surrounded by
a number of others of much smaller dimensions, and of a
drop-like form, so set as to radiate around the principal
vesicle as a centre, the rounded portion of each in appa-
rent contact with the vesicle, and the slender extremity
running off as an attenuated point till lost to sight in the
sarcode. The main vesicles alternately become distended,
and suddenly contract to a point ; while the radiating cells
are continually varying in size, though in a less degree.
It is customary to describe the secondary vesicles as coming
into view at the instant of the contraction of the primary
PARAMECIUM.
one, and to suppose that the emptying of the one is the
filling of the other, but I have not been able to observe
this mutual relation satisfactorily made out. The smaller
as well as the larger vesicles are conspicuous from their
colourless transparency ; for the general sarcode of the
body, though pellucid, is only so in the same degree as
glass, slightly smoked; besides that its clearness is often
impaired by crowds of granules and minute globules.
You ask what is that comparatively large oval body
attached by its side to one of the leaves of the plant. It is
the egg of some considerable Rotifer, probably JSuchlanis,
which is always glued to some filament or stem of a water-
plant. It may interest you to watch the progress of the
contained embryo, which you can readily do, since the egg-
shell is as transparent as glass, and the infant animal
already displays the movements of independent life.
INFUSORIA.
399
Meanwhile I will tell you the tragical and lamentable his-
tory of just such an embryo as this, that, was eaten up
before it was born, under my own eye. One of the depre-
dators was a very amusing animalcule, which is sufficiently
scarce to make its occurrence a thing of interest, espe-
cially to a young microscopist, as I was at the time.
A large egg of (as I believe) Eucltlanis dilatata had been
laid during the night on a leaf of Nitella, in the live-box.
When I observed it, the
transparency of the shell
allowed the inclosed ani-
mal to be seen with its
viscera, which occasion-
ally contracted and ex-
panded ; the place of the
mastax I could distinctly
make out. The cilia were
vibrating, not very ra-
pidly, but constantly, on
the front, where there
was a vacant space between the animal and the shell.
From seven a.m. when I first saw it, I watched it for about
eight hours, without perceiving any change ; but at that
hour having withdrawn for a short time, I perceived on
my return that a portion of the animal was outside the
shell. The appearance was that of a small colourless
bladder oozing out at an imperceptible aperture ; and this
oval vesicle quickly but gradually increased, until it was
half as large as the egg itself. A little earlier than this
point, the cilia were seen on the front or lower side of the
excluded portion, and these began to wave languidly in a
hooked form. They thus seemed much longer and more
substantial than when rotating in the perfect animal.
When excluded to the extent just named, some little crea-
tures that were flitting about found it, and began to
assemble round it. These were far too rapid in their
COLEPS AND CHIL01IONAS.
400 EVENINGS AT THE MICROSCOPE.
movements to allow me to identify them before, or to per-
ceive anything else than their swift motion and oval form ;
but this attraction, causing them to become still, allowed
me to perceive their singular and beautiful structure.
Each consists of an oval vase open at the top, the margin
of which is cut into a number of little points; the sides are
marked by a series of ribs, which run down longitudinally,
and are crossed by other transverse ones ; the rounded
bottom is furnished with three short points, so that the
whole reminded me of a barrel with its staves and hoops,
set on a three-legged stool. Within the body, which is
colourless, are seen small dark spots which are probably
the stomach- vacuoles. Thus I identified these little barrels
with Coleps hirtus of Ehrenberg, but I found no record of
their carnivorous propensities. One after another whirled
into the field, and after a few gyrations became stationary
at the head of the half-born Euchlanis, just as I have seen
vultures gather one by one to a carcass. Very soon there
were a dozen or fifteen of them, some of which were ever
shifting their places, and some were playing around, or
revolving on their longitudinal axes. I found that their
object really was to prey on the soft parts of the creature
just excluded from the egg; for, by carefully watching one,
I distinctly perceived particles of the flesh fly off, as it
were, and* disappear in the body of the Coleps. The
appearance was that of steel filings drawn to a magnet, for
the mouth of the Coleps was not in actual contact with the
flesh; and therefore, I suppose, the surface having been in
some way ruptured (which I could see it was), the loose
gelatinous atoms were sucked off by a strong ciliary
current. They did not attack any other part, and after
having continued their murderous occupation about ten
minutes, they one by one departed. The ciliary motion
of the Euchlanis ceased immediately after it was first
attacked, and I suppose it was soon killed, for it did not
increase in size in the least afterwards. When the Colepes
INFUSORIA. 401
left it, a great portion, perhaps a third, of the excluded
parts was devoured.
As soon as the depredators were gone, or even before,
others more diminutive, but more numerous, were ready
to take their place. The drop of water under review had
been found amazingly full of a small oval Jlonas, perfectly
transparent, of an oval form, with some granules visible in
the interior. They were about -joVo °^ an ^nc^ ^n length.
They filled the whole field, gliding about very nimbly, but
so close as but just to allow space for motion, and that in
several strata. By the morning these were collected in
masses, which to the naked eye looked like little unde-
fined white clouds, but which under the microscope
showed the Monads in incalculable multitudes, but for
the most part in still repose. Some were seen moving
to and fro, however, and, in the course of the day, most
of them became again active. As soon as the Colepes
had forsaken their prey, the Monads began to gather
round it, cleaving to the same parts, and apparently
imbibing the juices, for the extruded parts still slowly
decreased, until at length these were reduced to about
one-third of their original dimensions.
A close examination of these latter when they had
settled to rest showed me that they were of the species
Chilomonas iKiramozcium. There is an indentation on
one side of the front where the mouth is situated: here
there is a ciliary action ; the projecting part, called the
lip, is said to be furnished with two slender flexible pro-
boscides, but my power was not sufficient to discern any
trace of these. A sort of a ridge, or keel, runs down the
length of the body, perceptible by a slight line ; numbers
of stomach-cells also are perceptible. The motion of
these lip-monads was not very rapid when unexcited •
it is performed by a sort of lateral half-roll, the two
sides alternately being turned up, like a boat broadside
to a swell, and the line of progression is undulating.
2 D
402
EVENINGS AT THE MICROSCOPE.
And now, having pretty well exhausted the contents
of this live-box, let us try a dip from this other phial
from another locality, equally productive, if I am not
mistaken. Yes; for, to begin, the stalks of Nitella here
are fringed with populous colonies of the most attractive
of all the Infusoria, the beautiful Vorticellce. The species
is not the common bell-shaped one, but the smaller with
pursed mouth, the little V. microstoma.
Look at this active group, consisting of a dozen or so
of glassy vases, shaped something like pears, or elegant
YOETICELX^:.
antique urns, elevated on the extremities of long and
very slender stalks, as slender as threads, and about six
times as long as the vases. The stalks grow from the
midst of the floccose rubbish attached to the plant, and
diverge as they ascend, thus carrying their lovely bells
clear of one another.
Each vase is elegantly ventricose, or swollen, in the
INFUSORIA. 403
middle, terminating below in a kind of nipple to which
the stalk is attached, and above in a short wide neck with
a thickened rim. This last is highly sensitive and con-
tractile ; its inner edge is set round with a circle of
vibratile cilia, which, when in full play, produce a pair of
small circular whirlpools over two opposite points of the
brim. The cilia themselves cannot be distinguished, but
their optical expression is curious. At the two opposite
points of the circular margin, as seen in perspective when
slightly inclined towards the observer, viz., at those points
where the cilia, from their position with regard to the
eye, would be crowded together, there are seen two dark
dashes, representing, doubtless, two ciliary waves, but
which have all the appearance of tangible objects, some-
times withdrawn, sometimes protruded, and often
vibrated with a rapid snatching movement.
These vases are of the usual appearance in Infusoria.
Their substance is the clear transparent colourless sarcode,
but it contains within it more or less of the cloudy
nebulous matter which we have been lately familiar with.
There are several globular vesicles or vacuoles, some ready
to imbibe colour from pigment, and others already occu-
pied with brown food ; while in each case we see, near
the centre of the vase, a longish body of clear granular
texture, which is called the nucleus, and which seems to
play an essential part in the vital economy of the animal.
The movements of a group such as that we are looking
at are very sprightly and pleasing. The vases turned in
all directions, some presenting their mouths, some their
sides, some their bases, to the eye ; inclined at various
angles from the perpendicular, and bending in diverse
degrees upon the extremity of their stalks; swaying
slowly and gracefully to and fro, as driven hither and
thither by the ciliary currents; and, above all, ever flying
up and down within the length of their radius, as a bird
when confined by a string ; — all these circumstances
2 d 2
404 EVENINGS AT THE MICROSCOPE.
impart a charm to this elegant animalcule, which enables
us to look long at it without weariness.
This last movement is peculiar, and worthy of a
moment's closer examination. The stalk, when extended
to the utmost, is an elastic glassy thread, nearly straight,
like a wire, but never so absolutely straight as not to show
slight undulations. The stalk, when thus drawn tight, is
highly sensitive to vibrations in the surrounding medium ;
and as in the circumstances in which we observe the
animals, such vibrations must be every instant communi-
cated to the vessel in which they are confined, the stalks
are no sooner fully extended than they contract with
alarm. This depends on a contractile cord which passes
throughout the entire length of the stalk, and which is
distinctly visible in the larger species as a narrow band.
We can scarcely err in considering this ribbon as a rudi-
mentary form of muscle, though we do not recognise
in it some of the characteristic conditions which we are
accustomed to see in it in higher animals.
The contraction of the muscle is very sudden, energetic,
and complete. With a rapidity which the eye cannot fol-
low, the vase is brought down almost to the very base of the
stalk. Then it slowly rises again ; and now we see, what we
could not discern in the act of contraction itself, that in
that act the stalk was thrown into an elegant spiral of many
turns, which at the utmost point of contraction were packed
close on each other, but which in the extending act gradu-
ally separate, and at length straighten their curves.
In any stage of the extension, the sudden contact of
the vase with any floating or fixed object apparently
causes alarm, and induces the vigorous contraction; but
vibrations, even when so violent as those produced by
tapping the stage of the microscope with the finger-nail,
have no effect unless the stalk be tense, its own power
of vibration being then only developed, just as a cord
becomes musical in proportion to its tension.
INFUSORIA. 405
It is not until we view these creatures with a good
microscope that we acquire an adequate idea of their
beauty : for myself, at least, it was so. I had seen
engravings of many of the invisible animalcules, and had
read technical descriptions ; but of their brilliant trans-
parency, their sudden and sprightly motions, their general
elegance and delicacy, and the apparent intelligence with
which they are endowed, neither books nor engravings
had given me any conception.
Some of the individuals under our present examination
are exhibiting phenomena of no less interest than their
form and motions. Some of the stalks are terminated
by two vases instead of one, which appear to spring from
a common point. These, however, are the result of the
spontaneous splitting of one; and in other examples you
may see the process in different stages ; or, if your patience
endure a couple of hours' watching, you may trace the
whole phenomena, as I have done, from the moment
when it first becomes perceptible, to its completion in the
freedom of one of the newly-formed animalcules.
For instance, you perceive that one of the bells instead
of being vase-shaped has assumed a globular form. By
keeping your eye on this for only a few moments, you de-
tect a depression forming in the midst of its front outline,
which momentarily deepens, until it is manifestly a cleft.
The division proceeds downwards, the two halves healing
simultaneously, so that they are at all times perfectly
smooth and rounded; at length two vases appear, side by
side, where a few minutes before there had been but one.
One of these is destined to be ultimately thrown off,
while the other retains sole possession of the stalk. You
soon see which it is that is going to emigrate: for, though
the two are alike in size, the roving one early closes the
mouth of the vase, becoming smooth and globular there,
never to open again. The cilia, now therefore become
useless, disappear by absorption ; but meanwhile a new
406 EVENINGS AT THE MICROSCOPE.
circle of these organs is developed around the basal ex-
tremity of the vase, and these, every instant becoming
more vigorous in their motions, sway the little globe about
on its point of attachment. At length the connexion
yields, breaks, and the animalcule shoots away, rowed
by its hundred oars, to find a new abode, and to found a
new colonv.
Here and there you see shooting through the group,
with a rapid gliding movement, an oblong clear body.
This is one of the vases, formed by self-division, and
exercising its newly-found power of locomotion. It is
giddily roving hither and thither, until the instinct of
wandering ceases, when it will soberly settle down, affix
itself by the point which was formerly its mouth, whence
a new stalk will gradually grow, and opening a new
mouth in the midst of the new crown of cilia,
I believe that the division is sometimes transverse in-
stead of longitudinal, the cleft occurring by constriction
across the middle of the vase; but this I have not seen.
In whatever direction it takes place, it is essential that
the oblong granular body, called the nucleus, which you
see in each vase, be divided, the cleft passing through
the middle of this substance, a portion of which is there-
fore appropriated to each new-made animal.
That the essential vitality of the creature resides in
this nucleus is shown by another and highly curious
mode of increase, namely, that which is effected by
encystion. Let us search the live-box carefully ; for,
amidst so great a profusion of Vorticellce as we have on
this Nitella, it will go hard if we do not find some
individuals in the encysted stage.
Look at this elegant object. It resembles a trumpet
of the clearest glass, with a rounded extremity, and with
the base affixed to the weed, from which it stands up
erect. Within the expanded part of the trumpet there is a
turbid mass, with a perfectly defined outline, from several
INFUSORIA.
407
points of which proceed radiating pencils or tufts of
long, straight, stiff, elastic filaments, like threads of
spun glass, varying greatly in length, and each ter-
minated by a little knob of the same material. The
tout ensemble of this object is very attractive and beau-
tiful, and its history is a tale of marvels.
No wonder that Ehrenberg, supposing this form to be
ACIXETA.
an independent animal, gave it a generic and specific
name. He called it Acineta mystacina. For who would
have suspected that this stiff* and motionless object, with
its tufts of flexible but inanimate threads, had any con-
408 EVENINGS AT THE MICROSCOPE.
nexion with the sprightly vases which we have been
examining 1 Yet it is the same animalcule, in what we
may, with a certain liberty of phrase, call its chrysalis
condition !
The history of the Vorticella, as it has been elaborately
worked out by Dr. Stein, exhibits phenomena analogous
to those marvellous changes which we lately considered
under the appellation of the Alternation of Generations.
Large individuals withdraw their circle of cilia, close up
the mouth, and become globular, and then secrete from
their whole surface a gummy substance, which hardens
into a spherical transparent shell called a cyst, inclosing
the Vorticella in its cavity. Within this cyst is seen the
hand-shaped nucleus, unchanged, and what was the con-
tractile bladder, which, however, no longer contracts.
By-and-by this torpid Vorticella enlarges itself irregu-
larly, pushing out its substance in tufts of threads, and
frequently protruding from one side a larger mass, which
becomes an adhering stalk. Thus it has become an
Acineta, such as we now behold.
From this condition two widely different results may
iproceed. In the one case, the encysted Vorticella sepa-
rates itself from the walls of the Acineta, contracts into
an oval body, furnished at one end with a circle of
vibratory cilia, by whose movements it rotates vigorously
in its prison, while the more obtuse end is perforated by
a mouth leading into an internal cavity. In the interior
of this active oval body there are seen the band-like
nucleus, and a cavity which has again begun to contract
and to expand at regular intervals. It is, in fact, in
every respect like a Vorticella vase, which has just freed
itself from its stalk. Presently, the perpetual ciliary
action so far thins away the walls of the Acineta that
they burst at some point or other, and the little Vorti-
cella breaks out of prison, and begins life afresh. The
Acineta, meanwhile, soon heals its wound, and after
INFUSORIA. 409
a while develops a new nucleus, which passes through
the same stages as I have described, and bursts out, a
second Vorticella.
But the cycle of changes may be quite different from
this. For sometimes the nucleus within the Acineta, in-
stead of forming a Vorticella, breaks itself up into a great
number of tiny clear bodies, resembling Monads, which
soon acquire independent motion, and glide rapidly about
the cell formed by the inclosed Vorticella-body as in a
little sea. But, by-and-by, this body, together with the
Acineta wall, suddenly bursts, and the whole group of
Monad-like embryos are shot out, to the number of thirty
or upwards. The Acineta now collapses and disappears,
having done its office, while the embryos shoot hither
and thither in newly-acquired freedom. It is assumed,
on pretty good grounds, that these embryos soon become
fixed, develop stalks, which are at first not contractile,
and gradually grow into perfect Vorticellce, small at the
beginning, but capable of self-division, and of passing
into the Acineta stage, and gradually attaining the full
size of the race.
Some forms of the same family, Vorticellada>, are
interesting as dwelling in beautiful crystalline houses,
of various shapes, always elegant. All these have been
ascertained to pass through the same or similar A cineta
stages. Cothumia imberbis is one of the prettiest of
these. The cell is of an elegant ampulla-like form, per-
fectly transparent and colourless, set on a stiff foot, or
short pedicle, which shows many transverse folds, like
those of leather. From the mouth of the vase projects
the animal, whose form may be distinctly traced through
the clear walls of the cell attached to its bottom, whence
it stretches upward when seeking prey, or to which it
shrinks when alarmed.
In the former condition the body resembles a much
elongated Vorticella, with a similar circular orifice, set
410
EVENINGS AT THE MICROSCOPE.
round with cilia. Often the animal performs its ciliary
vibrations within the shelter of its house, not venturing
to protrude beyond its rim. If carmine has been mixed
with the water, the atoms are seen in the customary
vortex, and some are occasionally drawn into the cell
nearly half-way down its cavity, and then swiftly driven
out again. On a slight tap upon the table the animal
withdraws, and in the same moment the urn bends clown
upon its leathery pedicle, at a point w^here there is always
an angle, until the rim of the cell is in contact with the
plant to which it is attached. This action is instan-
taneous. Presently, however, it rises, and resumes its
former position, and then the mouth of the cell slowly
opens, and the animal again protrudes, the cilia appear-
ing first, and finally the head or front part of the animal,
which is then opened and begins to rotate.
Very similar to this are the Vaginicolce, but the cells
which they inhabit are not stalked, but are immovably
affixed to plants. In V. crystalline^ the cell is a tall
VAGI-MCOLA.
goblet, standing erect, perfectly colourless ; while in
V. decumbens, it is slipper-shaped, attached along its
sides, and of a golden-brown hue, but still quite trans-
parent. Here is, fortunately, a group of the latter
species, scattered about the leaves of the Xitella.
Though, in general, both in form and habits, closely
INFUSORIA. 411
like the Cothurnia, yet the Vaginicola has some peculia-
rities of interest. The cilia are more developed, and
can be more distinctly seen than in either Cothurnia
or Vorticella, forming, when in swift action, a filmy
ring above the margin, along which, as if upon a wheel,
one or more dark points are frequently seen to run
swiftly round : the optical expression, as I presume, of a
momentary slackening in the speed of the wave. The
act of self- division takes place in this animal, as in the
Vorticella; and it is curious to see two Vaginicoke,
exactly alike, lovingly inhabiting the same cell. One of
the cells which we are now examining is in this doubly-
tenanted condition.
I will now exhibit to you some examples of the most
highly-organised forms of this class of animals, in which
we discern a marked superiority over any that we
have yet looked at, and a distinct approach to those
animals whose more precise movements are performed
by means of special limbs. These creatures are very
common, both in fresh and sea water, wherever vegetable
matter is in process of decomposition; and hence their
presence can at all times be commanded by keeping
infusions. In this old infusion of sage leaves, for
instance, they occur in vast multitudes, past all imagi-
nation, as you may see with a lens in this drop.
This group belongs to the genus Stylonychia, and, as I
believe, to the species S. pustulata. It presents the form
of an oval disk, which, when seen sidewise, is found to be
flat beneath and convex above. It commonly swims with
the belly upwards, and, when exhibited on the stage of
the microscope, in almost every case, this surface is pre-
sented to the eye. It darts about very irregularly, with
a bobbing motion, rarely going far in one direction, but
shooting a little distance, and then instantly receding,
turning short round, and starting hither and thither, so
fitfully that it is very difficult to obtain a fair sight of its
412 EVENINGS AT THE MICltOSCOPE.
structure. Its margin, however, is surrounded by short
cilia; the mouth, which is a long opening on the front
part, and at the left side (as to the animal) of the ventral
surface, is fringed with long cilia, which are continually
vibrating. These are the organs of the darting motion;
but the creature crawls, like a mouse, along the stems of
conferva, Szc, which it performs by means of curved spines,
called uncini, near the front part, the points of which are
applied to the stem, and also by long stiff styles or bristles,
which project backward and downward from the hinder
part. Sometimes the animalcules crawl for a moment
back downward on the inner surface of the glass cover,
when the bases of the anterior curved spines appear
dilated like large spots. The spines are not capable of
much action, but they are rapidly used. The general
appearance of the creature reminds us of the little Wood-
louse or Armadillo of our gardens. The interior of the
body is occupied with a granular substance, in which are
scattered many globular vesicles of different sizes. The
animal is very transparent, and almost colourless. They
increase very fast by transverse division, which is per-
formed under the microscope, so as greatly to increase
the number under examination, even in an hour or two.
A constriction forms in the middle of one, which quickly
deepens, dividing the oblong creature into two of circular
iigure. The mouth of the new one, with its vibratile
cilia, is formed long before separation is complete, and at
the same end and side as in the parent. The styles and
bristles then form, and the creatures are held together
for a few seconds by these organs, even when the bodies
are distinctly severed. When separated, they retain the
round form for some time.
When a drop of such water is examined between two
plates of glass, it is amusing to observe the numbers that
congregate in the little pools left by the gradual drying of
the fluid. This probably becomes unlit for respiration
INFUSORIA. 413
for the motion of the cilia becomes more and more languid,
and the creatures die before the water is dry. They not
only die,hutva?iish ; so that, — where there were scores, so
close that in moving they indented each other's sides and
crawled over one another, — if we look away for a few
minutes, and again look, we see nothing but a few loose
granules. This puzzled me, till I watched some dying,
and I found that each one burst and, as it were, dissolved.
The cilia moved up to the very last moment, especially the
strong ones in front, until, from some point in the outline,
the edge became invisible, and immediately the animal
became shapeless, and from the part which had dissolved
the interior parts seemed to escape, or rather the skin, so
to speak, seemed to dissolve, leaving only the loose viscera.
From the midst of these then pressed, as if by the force
of an elastic fluid within, several vesicles of a pearly
appearance, varying in number and size, and then the
whole became evanescent.
You will have observed that the admixture of carmine
to the water, while the animalcules were active, shows the
direction of the ciliary motion with great distinctness.
The particles form two eddies, one on each side of the
front, which meet in the centre in a strong current, and
pass off behind the mouth on each side. We do not
perceive that any of them swallow the particles of
carmine, for the internal vessels remain colourless.
I have found that if a drop of water containing these
animals be placed on a slip of glass exposed to the open
air, they do not burst as the water dries away, but dry
flat on the glass, their bodies broader but shorter than
when alive, and quite entire. Their cilia are then very
manifest. On being again wetted, though after only
a few minutes' desiccation, I have never been able to
revive them, nor any other Infusoria in like circum-
stances, notwithstanding what is stated in books.
Here is another species in equally amazing profusion,
414 EVENINGS AT THE MICROSCOPE.
S. mytilus. Its form is oblong, with rounded extremities,
the anterior obliquely dilated. This species affords a good
example of the various organs of locomotion. A trans-
parent oblong shield, which is quite soft and flexible, is
spread over the back, which does not prevent our eyes
discerning all the organs through it ; though, much more
commonly, the animal, when under the microscope, crawls,
belly upward, beneath the glass cover of the live-box.
Around the anterior part, which is broadened, are placed
cilia, which are vibratile ; these are continued round the
mouth, a sort of fold on the side. Towards the posterior
extremity on each side are other rows of cilia, which being-
large are well displayed. On the ventral surface, chiefly
towards the front part, are seen several thick pointed
processes, shaped like the prickles of a rose, but flexible,
and capable of being turned every way. These are the
ttncini, and are evidently used as feet, the tips being
applied to the glass. The optical effect of the throwing
about of these uncini, when the place which they touch
is in focus, is very curious. They are rapidly moved, but
without regularity ; the tips bend as they touch the
surface of the glass ; some of them seem to have accessory
hairs, equally long, but slender, proceeding from the
same base. On the hinder quarter of the ventral surface
are several thick pointed spines; these are inflexible, nearly
straight, placed side by side, but not in regular order,
some reaching beyond others. I have not seen these used,
but they commonly remain sticking out in a horizontal
direction. These organs are termed styles. Besides
these, there are three slender bristles, called setce, placed
at the hinder extremity, the central one in the line of the
body, the others radiating at an angle. These are dis-
tinguished from the cilia, not only by their length, but by
not being vibratile. The motions of these animals are
powerful, but, irregular and fitful, very much like those of
the former species. They dart hither and thither, back-
INFUSORIA. 415
ward as well as forward, occasionally shooting round and
round in a circle, with many gyrations, much like the
pretty little polished bettles (Gyrinus) that play in mazy
dances on the surface of a pool. The two extremities
seem covered with minute pits or stipplings, but colour-
less ; the central part is occupied with yellowish granules
of different sizes.
I once witnessed the dissolution of one of these animals
under peculiar circumstances. Two or three stems of
an aquatic plant had become crossed in the live-box so
as to form an area, into which the Stylonychia had
somehow introduced himself. There was just room for
him to move backward and forward without turning,
and the space was about three times his own length.
Within this narrow limit he impatiently continued
crawling to and fro, moving his uncini with great
rapidity, and showing their extreme flexibility ; for, as
he applied them now to the stem, now to the surface of
the glass, these whip-like uncini were sometimes bent
double. The so-called styles at the posterior extremity,
though less frequently used so, were yet occasionally
bent and applied to the surface as feet, so that they are
certainly not inflexible as supposed, nor do I see any
essential difference between them and the uncini. The
whole body was flexible, taking the form of any passage
or nook into which it was thrust, yet recovering its
elasticity immediately the pressure was removed. Its
proper form appeared to be convex above and concave
beneath, rather than flat. After having been thus
employed about half an hour under my observation, it
became still, moving only its cilia, when I left it a little
while, and on my return found that it was dissolved ;
the outline having entirely disappeared, and nothing
being left but the granules, and globular vesicles, that
had constituted its viscera, some of which still contained
the carmine which had been very perceptible in the
416
EVENINGS AT THE MICROSCOPE.
living animal. This was the more remarkable, as there
was plenty of water. It looked like suicide, — a spon-
taneous choosing of death rather than hopeless captivity.
Common as these Stylonychke are, and abundant be-
yond all calculation, where they do occur, from their
tendency to self-division, they are not so universally
met with as their cousins, of the genus Euplotes. These
are still more highly organised, and will please you by
their activity and sprightly intelligence, I am sure. Here
are several individuals in the live-box at this moment.
They differ from the Stylonychice, in having the soft
body covered with a plate of crystal mail, hard and
inflexible, much like the shield of a Tortoise. Several
species have this glassy shield marked with delicate lines
running lengthwise ; sometimes in the form of parallel
ridges, as in a little species found in infusions (perhaps
E. char on), at others forming rows of minute round knobs,
as E. truncatus, the species now before us. The shield is
ample, considerably overlapping the soft body ; it rises
into an arched form in
the centre ; and is more
or less round or oval.
The mouth is oblique,
and extends a long way
clown the under surface ;
it is set with strong and
fine cilia, which also
spread over the front.
The orgai, r of motion
are, as before, long styles, pointed and rather stiff pro-
cesses, which project from beneath the shell backwards
and downwards, and soft hook-like uncini, which are set
chiefly near the fore part of the inferior surface. In the
species before us these are about six or seven in number,
but in E. char on they are more numerous. The twinkling
rapidity with which these little feet are applied to the
EUPLOTES.
INFUSORIA. 417
surface in crawling affords a pleasing siglit : particularly
when the animal is running back-downwards on the upper
glass plate of the live-box. Some species have bristles
(or setcp) affixed to the hinder part of the shell, from which
they diverge. In E. truncatus these are four ; but they
are wanting in E. charon. The body displays a mass of
granules, vacuoles, and vesicles of different sizes.
These are very beautiful objects ; and their sprightly
motions and apparent intelligence give them an additional
interest. They crawl more than they swim, running with
great swiftness hither and thither, frequently taking short
start?, and suddenly stopping. The specimens which we
are examining are taken from wTater which had been kept
in a jar for several weeks. The vegetable matters are
decaying; and among the stems and filaments this pretty
species crawls and dodges about. It seems reluctant to
leave the shelter of the decaying solution; sometimes one
will creep out a little way into the open water, but in
an instant it darts back, and settles in among the stems
and flocculent matter. Any attempt by turning the glass
cover to bring it out into view only makes it dive deeper
into the mass, as if seeking concealment. This is about
TT—y of an inch in length of lorica ; and the E. charon
is not more than one-fourth of this size. These creatures
remind one of an Oniscits, especially when in profile.
There is an animal very closely allied to these, but
much more beautiful, being of a clear greenish trans-
lucency, with several vesicles filled with a rose-coloured
or purple flu.d of much brilliancy. This creature, which
bears the name of Chlamidodon, has the peculiarity of a
set of wand-like teeth arranged in a hollow cylinder.
And with these we dismiss the Infusoria, a class of
animals which, from their minuteness, the number and
variety of their species, their exceeding abundance, the
readiness with which they may be procured, and, as it
were, made to our hand (by simply steeping vegetable
2 E
418 EVENINGS AT THE MICROSCOPE.
matter in water), and the uncertainty which still prevails
concerning many parts of their structure and economy ;
and therefore, concerning their true affinities in the great
plan of creation, — offer one of the most promising fields
of research which a young microscopist could cultivate.
These are Thy glorious works, Parent of good,
Almighty ; Thine this universal frame,
Thus wondrous fair. Thyself how wondrous then !
Unspeakable, Who sitt'st above these heav'ns,
To us invisible, or dimly seen
In these Tliy loicest works; yet these declare
Thy goodness beyond thought, and power divine.
THE END.
INDEX.
Acineta, 407.
Acontia, 356.
Air-tubes of Fly, 95.
Alcyonium, 3-49.
Alternation of Generations, 324,
Bug", mouth of, 143.
Bugula, 64.
Butterfly, scales of, 79, 80.
sucker of, 153.
333.
Caryophyllia, weapons of, 364.
Amoeba, 378.
Chameleon-ny, 101.
Anchors of Synapta, 299.
Cheese-mite, 220.
Animalcules, 389.
Cnilomunas, 401.
Antennae of Chafer, 162.
Chirodota, 298.
Crab, 171.
Cicada, drum of, 89.
Fly, 166.
ovipositor of, 136.
Gnat, 166.
Cilia of Cydippe, 310.
Insects, 158.
Infusoria, 397, 4l)3, 409.
Moths, 163.
Rotifera, 223, 252.
Skipjack, 163.
Cinclides, 358.
Weevil, 160.
Cnidse, 342, 356.
Aphrodite, 263.
Cockchafer, antennre of, 162.
Arcella, 383.
spiracle of, 100.
Coleps, 399.
Barnacles, 192.
Contractile Bladder, 250, 380,
hand of, 192.
397.
transformations of, 195.
Corkscrew Coralline, 63.
Bee, eyes of, 170.
Corynactis, weapons of, 369.
foot of, 119.
Cothurnia, 409.
mouth of, 142.
Cow's paps, 349.
sting of, 125.
Crabs, 1/1.
wing of, 73.
ears of, 172.
Beetle, mouth of, 138.
eyes of, 174.
"Bird's-head," 64.
stages of, 182.
use of, 68.
Crane-tiy, spiraclu of, 99.
Blood of Beasts, 27.
Craspeda, 364.
Birds, 28.
Cricket, drum of, 85.
Fishes, 28.
Cuckoo-fly, ovipositor of, 128.
Frog, 29.
Cuttle-shell, 39.
Man, 27.
Cyclops, 175.
Beptiles, 28.
Cydippe, 308.
Tunicata, 33.
Cypris, 180.
Brachionus, 225.
Bristle-tail, scales of, 77-
Daphnia, 178.
420
EVENINGS AT THE MICROSCOPE.
Dead-men's fingers, 349.
Diamond-beetle, scales of, 83.
Dragon-fly, 71.
eye of, 166.
Dumb-bells of Holotburia, 297.
Dyticus, foot of, 117.
Earthworm, 259.
Ecthoreum, 366.
Egger-moth, 163.
Euglena, 389.
Eunice, 268.
Euplotes, 416.
Eyes of Crab, 174.
Dragon-fly, 166.
Harvestman, 209.
Infusoria, 389.
Insects, 166.
Eotifera, 236, 389.
Scallop, 50.
Snail, 54.
Spider, 207.
Feathers, structure of, 15.
Fission of Infusoria, 394, 405.
Flea, mouth of, 146.
Fly, antenna) of, 166.
flight of, 70.
foot of, 115.
spiracle of, 9S.
tongue of, 151.
wing of, 72.
Foot of Actinurus, 249.
Bee, 119.
Beetle, 117.
Brachion, 227.
Dinocharis, 241.
Fly, 109.
Silkworm, 123.
Spider, 217.
Whiptail, 239.
Foraminifera, 383.
Frog, blood of, 31.
Froghopper, ovipositor of, 135.
Galathea, 186.
Gall-fly, egg-tube of, 12S.
Gnat, antennte of, 166.
grub of, 103.
mouth of, 149.
wing of, 74.
Grantia, 386, 38S.
Grasshopper, sounds of, 86.
Hair of Bat, 12.
Bee, 14.
Beetle, 14.
Hair of Cat, 8.
Hog, 5.
Horse, 7.
Man, 2.
Mole, 9.
Moth, 14.
Mouse, 11.
Sable, 9.
Sheep, 7.
Halichondria, 385.
Harvestman, 209.
Heart-urchin, 292
Horse-fly, mouth of, 145.
House-fly, 70.
Humble-bee, 71.
Hydractinia, 334.
Infusoria, 389.
Insects, 70.
air -tubes of, 93
antennce of, 158.
eyes of, 166.
feet of, 109.
mouths of, 138.
sounds of, 84.
stings, etc., of, 125.
Jelly-fish, 307.
Katedid, 86.
Laomedea, 326.
medusoids of, 331.
Lares, 345.
Larva of Urchin, 301.
Leech, 269.
Limpet, tongue of, 46.
Locomotion, variety in, 25S.
Lombrinereis, 268.
Luminosity of Medusa, 319.
Lynceus, 177.
Madrepore, weapons of, 364.
Mastax, 233.
Medusae, 307.
transformations of, 333.
Medusoids of Laomedea, 331.
Stauridia, 343.
Megalopa, 182.
Mite, cheese, 220.
water, 222.
Mollusca, ears of, 55.
eyes of, 51.
shells of, 39.
tentacles of, 50.
tongues of, 46.
Moths, antenna of, 163.
INDEX.
421
Moths, scales of, 79, 81.
Mouth of Bee, 142.
Beetle, 138.
Brachion, 230.
Bug, 143.
Flea, 146.
Gnat, 148.
House-fly, 151.
Sea-worm, 267.
Sword-bearer, 246.
Tube-wheel, 251.
Whiptail, 238.
Murder, discovery of, 25.
Nacre, 43.
Nais, 262.
Nucleus of Infusoria, 406.
Nymphon, 218.
Otolithes of Medusae, 320.
Slug-, 56.
Ovipositor of Cuckoo-fly, 12S.
Gall-fly, 128.
Saw-fly, 131.
Paramcecium, 396.
Pearls, 44.
Pedicellarioe, 282.
structure of, 282.
use of, 288.
Periwinkle, eating of, 49.
tongue of, 50.
Perophora,
circulation in, 34.
respiration in, 36.
Phyllodoce, 266.
Pleasures of Sea-shore, 325.
Podura, scales of. 78.
Polymorphina, 383.
Polynoe, 262.
Polypes of Alcyonium, 350.
Hydractinia, 334.
Laomedea, 326.
Lar, 348.
Polystomella, 383.
Polyzoa, 60.
Proteus, 378.
Protozoa, 376.
Pseudopodia, 384.
Robber, story of, 2.
Pvotifera, 223.
abella, 343.
agartia, 356, 366.
Sarsia, 313.
Saw-fly, ovipositor of, 130.
Scales of Butterflies, 79.
Bristle-tail, 77.
Diamond-beetle, S3.
Flounder, 21.
Gnat, 75.
Gold-fish, 19, 24.
Perch, 17.
Pike, 23.
Podura, 78.
Sugar-louse, 77.
"Wrasse, 21.
Scallop, eyes of, 50.
Sea-anemones, weapons of, 315.
Sea-cucumber, 296.
dumb-bells of, 297
Sea-mat, 59.
Sea-mouse, bristles of, 264.
Sea-shore, pleasures of, 325.
Sea-urchin, spines of, 277.
larva), 301.
pedicellarice, 2S2.
pores, 290.
skeleton, 302.
suckers, 305.
Serpula, 271.
Shell of Cuttle, 39.
Pearl-oyster, 42.
Pinna, 42.
Shore-crab, 182.
Silkworm, foot of, 123.
spinner of, 157.
Skeleton Wheel-bearer, 241.
Slug, ears of, 55.
tongue of, 46.
Snail, eye of, 54.
Soicula of AJcyonium, 352.
Chirodota, 299.
Fish-scales, 24.
Holothuria, 298.
Sponges, 385.
Synapta, 299.
Spiders, eyes of, 207.
fangs of, 205.
foot of, 217.
habits of, 210.
silk of, 211.
spinner of, 213.
Spines of Heart-urchin, 292.
Sea-urchin, 277.
Spinner of Silkworm, 157.
Spider, 213.
Spiracles of Insects, 97, 106
Sponges, spicula of, 386.
Stauridia, 340.
Sting of Bee, 125.
V — — i
EVENINGS AT THE MICROSCOPE.
St}lonychia, 411.
Suckers of Sea-cucumber, 295.
Sea-urchin, 288.
Sugar-louse, 77.
Swan-neck, 393.
Sword-bearer, 246.
Synapta, 299.
Tentacle of Cydippe, 309.
Hydractinia, 339.
Laomedea, 329.
Scallop, 50.
Thaumantias, 319.
Thaumantias, 319.
Tongue of Butterfly, 151.
Fly, 151.
Limpet, 46.
Periwinkle, 46.
Slug, 46.
Trochus, 47.
Trachelocerca, 393.
Transformations of
Barnacle, 195.
Crab, 182.
Galathea, 18S.
Medusa, 323.
Polype, 324.
Sea-urchin, 301.
Tube-wheel, 256.
Vorticella, 408.
Tripod Wheel-bearer, 248.
Trochus, tongue of, 47.
Tube-wheel, 251.
Turris, 321.
Urchin, Sea, 276.
Vacuoles, 381.
Vaginicola, 410.
Vorticella, 402.
Water-fleas, 175.
Weapons of Anemones, 355.
Corynactis, 369.
Madrepore, 364.
Sea-worms, 262.
Weevil, 160.
Scales of, 83.
Wheel-bearers, 223.
Wheels of Brachionus, 226.
Chirodota, 298.
Whiptail. 238 .
Wing of Bee, 73.
Fly, 72, 84.
Gnat, 74.
Wool, 13.
Worms, 25S.
Zoea of Crab, 1S1.
Zoophytes, 325.
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