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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.



EVENINGS AT THE MICROSCOPE

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 rov-
ings, 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 cau-
tion, for it does not actually close the valves, unless it be
repeatedly disturbed, or unless the shock be violent, con-
tenting 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 two appearing like one undulating row
from the closeness of their proximity.

If you are familiar with the pin-cushions which chil-
dren often make with a narrow ribbon round the edges of
these very Scallop-shells, you can hardly 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 the two rows
of diamond-headed pins, carefully and regularly stuck
along the two edges of the pin-cushion ribbon the rib-
bon 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 dia-
monds.

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 is



MOLLUSC A: THEIR EYES 69

about to make its sudden and vigorous leaps, the gem-
meous 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 de-
servedly recognized in the projection of the bony ridge over
the human eye, which we call the brow, we surely cannot
fail to recognize, 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
in 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 colored iris perforated with a well-defined pupil,
and connected with a layer of pigment which lines the
sclerotic tunic a crystalline lens, and a vitreous humor
for the due refraction of the rays of light, and a retina
in their focus, formed by an expansion of the optic nerve,
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 lustrous points
every element needful for the due performance of vision,



70 EVENINGS AT THE MICROSCOPE

though, probably, the impressions thus conveyed may be
neither so powerful, nor so distinct, as those which are con-
veyed by the eyes of vertebrate animals. They are, how-
ever, we may be sure, amply sufficient for the wants of
the pretty Scallop, and are fresh proofs of the Divine wis-
dom and benevolence.

We have been accustomed, from childhood, to recog-
nize as eyes the shining black extremities of the upper
pair of "horns" in the Garden Snail. And though some
naturalists 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 sub-
stance, with which it is completely filled; toward the bot-
tom 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
humor. In the front part of the eye there is a crystalline
lens, a small, circular, flattish, or rather lenticular body,
perfectly clear and translucent, but a little more solid than
the vitreous humor.

Now protection for these so delicate organs is provided
in a way quite different from, yet equally effective with,



MOLLUSC A: THEIR EYES 71

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
most curious process of inversion. The action is performed
by means of a long muscular ribbon, which originates 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 ten-




STRUCTURE OF EYE IN SNAIL.



tacle 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 ten-
tacle, like so many rings throughout its whble 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, per-
haps, 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 color that we can readily



72 EVENINGS AT THE MICROSCOPE

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 compressorium, 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
comparative anatomist, familiar with the curious phenom-
ena 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 blad-
ders, without any opening, but filled with a clear fluid,
in which there are some minute bodies performing the
most extraordinary 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 acci-
dent touching the walls of the capsule in which they are
contained. If the capsule be ruptured, the motions in-
stantly 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 you may perhaps like to know a little more
about them.

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-



MOLLUSC A: THEIR EARS 73

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 toward this centre the otolithes
toward the circumference seem even to be violently urged,
their centripetal rush being invariably repulsed, and as
often driven again into a centrifugal direction. Eemoved
from the capsule, the motions of the otolithes instantly
cease. The cause of these curious oscillations remains un-
discovered. 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 uncili-
ated themselves, and, at the same time, distinguishes the
motion from that of inorganic molecules.

It has been more recently ascertained that the move-
ments 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 physiologists,
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
15 SCIENCE 4



74 EVENINGS AT THE MICROSCOPE

this is true with respect to the great majority, yet it may
be only that our senses are too dull to perceive the deli-
cate sounds which they utter, and which may be suffi-
ciently audible to their more sensitive organs; and, be-
sides, some Mollusca can certainly emit sounds audible
to us. Two very elegant species of Sea- slug, viz. Eolis
punctata and Tritonia arborescens, 1 certainly produce audi-
ble sounds. Professor Grant, who first observed the inter-
esting fact in some specimens of the latter which he was
keeping in an aquarium, says of the sounds that "they re-
semble very much the clink of a steel wire on the side of
a jar, one stroke only being 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 Tritoniae are lively and moving about, 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 ves-
sel, is mellow and distinct. ' ' The Professor has kept these
Tritoniae alive in his room for a month, and, during the
whcle 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 pro-
ceed from the mouth of the animal ; and, at the instant
of the stroke, we observe the lips suddenly separate, as if

1 Now called Dendronotus arborescens.



SEA-MATS AND SHELLY CORALLINES 75

to allow 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 be of an elec-
tric nature, they may be the means of defending from for-
eign enemies one of the most delicate, defenceless, and
beautiful Gasteropods that inhabit the deep." *



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. Fetch it: it is on the chimney-piece
upstairs.

Now all of these objects are not sea- weeds. I mean
they are not all plants; some of them are animals, and
these I want 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 silk-
worm'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-

1 "Edinb. Phil. Jour.," xiv. 186.



76 EVENINGS AT THE MICROSCOPE

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 mi-
nute shallow cells.

"Broad Horn wrack" and "Leafy Sea-mat" are the
names which the old collectors gave to this object; and
modern naturalists have given it the scientific appellation
of Flustra foliacea, and arrange it in the class Polyzoa, 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 neighbors 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



SEA-MATS AND SHELLY CORALLINES 77

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 thereabout. Yery well; a simple arithmetical process
shows that there are 1,680 cells in this square half -inch;
or 6,720 in a square inch. Now this very specimen, be-
fore I mutilated it, contained an area of about three square
inches; which would give 20,160 cells. This is the num-
ber on one surface; the other contains an equal number;
and thus you see that I have not exaggerated the popula-
tion 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 margin
is armed with short blunt spines, two on each side, which
stand obliquely erect, projecting outward 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 aggregation 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 gen-
erally they are scattered at more or less remote intervals.
If we now apply the microscope to these appendages, each
globule is seen to be flat on that perpendicular side which



78 EVENINGS AT THE MICROSCOPE

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 have examined 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 margin
all round, leaving a transverse opening just in the right
place viz., over the pillow and you would have ex-
actly 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
baby, with its little knees bent up to its chin, in that zig-
zag 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 will venture to affirm that a personal
examination of the creature itself would justify their cor-
rectness, and you would acknowledge that they could
scarcely be more apt.



SEA-MATS AND SHELLY CORALLINES 79

Moreover, the globular chambers show signs of life;
their front doors suddenly open, gape widely, and then
shut with a snap; and presently this opening and shutting
is repeated. The meaning of this action you will better
understand when we see analogous organs in 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




LEAFY SEA-MAT.

(A portion magnified.)



spines of the margin are not found on those cells tha*
carry the pearls; and, moreover, that they are also want-
ing on the approximate edges of the two cells that lie be-
hind every such pearl-bearing cell. Now the reason of
this omission is obvious. The spines projecting 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 agreeing
with this in all essential particulars of structure, though
widely different in form. The difference, however, is



80 EVENINGS AT THE MICROSCOPE

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 ex-
tent, 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, become segments of funnels; and
the peculiar elegance of this coralline 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-
times the Bird's-head Coralline, the latter name being as-
signed to it for a reason which you will presently perceive.
The appellation by which it is known to naturalists 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 nu-
merous polypides with the utmost activity and evident
enjoyment.

You gaze ; but you know not what you see. The pres-



SEA-MATS AND SHELLY CORALLINES 81

ence of many lines representing transparent vessels of strange"
and dissimilar shapes, overlying each other; and the sway-
ing to and fro of curious objects, which strike now and
then forcibly across the field of view, are quite bewilder-
ing. 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 mid-
dle 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 el-
liptical transparent space occupying nearly its whole sur-
face; this is covered with a very thin and elastic mem-
brane, 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,
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



82 EVENINGS AT THE MICROSCOPE

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



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