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body. As the young lies enclosed within the membranes
of the egg, the claws are folded on each other, and the tail
is flexed on them so far as the margin of the shield, and,
if long enough, is reflexed over the front of the shield be-
tween the eyes. The dorsal spine is bent backward, and
lies in contact with the dorsal shield ; for the young, when
it escapes from the egg, is quite soft, but it rapidly hard-
ens and solidifies by the deposition of calcareous matter
in what may be called its skin. The progress of this so-
lidification may be very beautifully observed by watching
the circulation in the 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 consoli-
dation advances, the circulation becomes more and more



CRABS AND SHRIMPS 215

limited in its extent, and is finally confined to the base.
These minute creatures, in this early state of their exist-
ence, are natatory and wonderfully active. They are con-
tinually swimming from one part of the vessel to the other,
and when observed free in their native pools are, if pos-
sible, 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 ves-
sel, to cast their shells, and acquire a new form. They are
exceedingly delicate, and require great care and attention
to convey them through the first stage; for unless the
water be supplied very frequently and in great abundance
they 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 sec-
ond transformation is marked by the disappearance of the
dorsal spine; the shield becomes flatter and more de-
pressed, the anterior portion more horizontal and pointed,
the three festoons having disappeared. The eyes, from
being sessile, are now elevated on foot- stalks, the infra -
orbital appendages become apparently converted into an-
tennae. 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 pos-
terior pair are branched near the base, and one of the
branches ends in a bushy tuft. The tail is greatly dimin-
ished in its relative size and proportions, and is sometimes



216



EVENINGS AT THE MICROSCOPE



partially bent under the body, but is more commonly ex-
tended. This form is as natatory 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 somewhat resembles a Q-alaihea." 1
Thus under Mr. Couch's eye the Zoea had changed to




SECOND STAGE OF SHORE-CRAB.



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 re-
semblance to that of the Sargasso Crabs (Grrapsidce)] for
the shield, instead of being large and arched in front, and
narrowed behind, was nearly square, while the front was

* "Rep. Cornw. Polyt. Soc.," 1843.



CRABS AND SHRIMPS 217

(taking in the eyes) almost straight, the lateral angles
much advanced.

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




THIRD STAGE OF SHORE-CRAB.



into the front margin, which would by degrees assume an
arched form, as you may see in this figure of the adult
Crab.

Though I cannot at this moment show you specimens
of the Garcinus in its earlier stages, yet I have here a
good number of the Zoeas of one of those intermediate
forms which are the connecting links between the Crabs
and Lobsters I mean Q-alathea. The adult animal is of
a broad squat form, something like what you might sup-
pose 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 brilliant scarlet
and azure paintings; but I cannot tell to which of them

all this infant form belongs.
15 SCIENCE 30



218



EVENINGS AT THE MICROSCOPE



You perceive that there is a general similarity between
these transparent little creatures and the Zoea described
by 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
spinules jointed to shoulder-like angles, and not serra-
tures. Its interior is perforated by a canal, which dilates




ADULT SHORE-CRAB.



and narrows irregularly. The carapace posteriorly is semi-
oval, projecting a transparent convex vault far over the
part where the abdomen is attached to it, as is seen when
the latter bends 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



CRABS AND SHRIMPS 219

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 hindermost pair of spines
are short, and are set close together, side by side. Be-
sides these jointed spines, each lateral angle of the caudal
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 exam-
ination.

The largest, during the few minutes which I have occu-
pied in the process of dipping them out, has undergone a
metamorphosis. You observed that, after skipping about
the trough for a few moments, it sank quietly to the bot-
tom, 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, need-
ing 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 por-
tion well defined. It is the appearance of these facets,
varying according as the perfectly hexagonal outline of



220 EVENINGS AT THE MICROSCOPE

each or the smooth and glossy convexity comes into focus,
that is so peculiarly charming.

Eeturning 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 dis-
tinctness, 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 be-
neath 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 colorless 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 pos-
terior 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 un-
attended 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 nowise explain.



BARNACLES 221



CHAPTEK 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 brown-
ish 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 toward
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 to-
gether in a peculiar manner, which are capable of separat-
ing, but which, when brought together, effectually close
up all ingress.

Perhaps you have never pushed your investigations
further than this, having a courteous respect for the feel-
ings of the inmate, which has prevented your intruding on
a privacy so recluse. But I have been less considerate;
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



222 EVENINGS AT THE MICROSCOPE

more intimate acquaintance with the little builders at
leisure.

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 speci-
mens of a much larger and finer species than the common
one the Balanus porcatus, 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
your 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 OD some one conveniently
placed for observation. It is now closed; but in a mo-
ment 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 ap-
paratus 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 reopen,
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



BARNACLES



223



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 antennae of a
Beetle. These fingers surround the mouth, which is placed
at the bottom of the sort of imperfect funnel formed 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 similar 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 be-
fore us, thirty-two joints, while the
shortest consists of about ten, the
intermediate ones being in propor
tion; so that the whole apparatus
includes nearly five hundred distinct articulations, a won
derful 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 supplied with nerves, which
lines the shell. 1 These hairs project at a more or less




HAND OF BARNACLE.



( Proc. Koyal Society," ix. 216.



224 EVENINGS AT THE MICROSCOPE

wide angle from the axis of the finger-like filament, and
are graduated in length; and what is very striking, as
illustrating the exquisite workmanship of the Divine hand,
the hairs themselves are compound structures ; for under a
high power they seem to be composed of numerous joints
an illusory appearance probably, what look like joints
being rather successive shoulders, or projections and con-
strictions of the outline while 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 toward their
attenuated extremities.

And now do you ask -What is the object of this elab-
orate contrivance, or rather series of contrivances? I
answer It is the net with which the fisher takes his food
it is his means of living. You have seen that the ani-
mal 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 de-
tail the construction of the net, you are prepared to appre-
ciate 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 or to curl up alternately, while
the number of the divergent fingers enables the animal
to grasp a comparatively large bulk of water in those curl-
ing organs. These, then, form a sieve; the water passes
through the interstices of the fingers, while the tiny atoms



BARNACLES 225

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 what-
ever is captured to the mouth.

But see how greatly the perfection of the instrument is
enhanced 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 cross-
ing their points, fill the interstices with an innumerable
series of finer meshes meshes of such delicacy that it is
next to impossible that any organized body enclosed in the
given area should escape.

But there is more in them than merely this minute and
widespread ramification. They are, as we have seen, or-
gans of touch; so that the net has not only the mechanical
power of capture, common to an inanimate cast-net which
a human fisher uses, but is endowed with the most exqui-
site sensibility in every part. The slightest contact of an
animalcule in the enclosed water with one of those thousands
of sensitive hairs, communicates instantly an impression to
the sensorium, and a consciousness of the fact to the Bar-
nacle; who is thus, without doubt, able with the quick-
ness 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 two
outer are horny and toothed, while the innermost is soft
and fleshy.

Fixed and immovable as the Barnacles are in their



226 EVENINGS AT THE MICROSCOPE

adult and final stage, they have passed by metamorphosis
through conditions of life in which they were active rov-
ing 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 porcatus, which for several days
past has been at intervals throwing out from the orifice of
its shell dense clouds of atoms, which form compact col-
umns reaching from the animal to the surface of the water.
One of these cloudy columns, when examined with a lens,
is seen to be composed of thousands of dancing creatures
resembling the Water-fleas that 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



BARNACLES 227

hurting it. The body is enclosed 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 downward
and backward, and the anal fork, which consists of a
bulbous base and two diverging points, which project be-
hind 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 im-
perfect joints, and the second and third pairs are double
from the basal joint outward, while the first pair are sim-
ple. 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 antennae.
This then is the first stage of the Barnacle the form under
which it appears when it is hatched from the egg.

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
kin have attained a more advanced form. Here is one,



228 EVENINGS AT THE MICROSCOPE

which by its superior size seems to have made some prog-
ress toward maturity.

Yes, here are more. These are evidently in their sec-
ond stage. There is an increase in length; for whereas
the former was only ifoyth of an inch in length, these have
attained to a length of irVth 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




YOUNG OF BARK ACLB.



cat 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 throw-
ing the extremity into the horizontal again. The deli-
cately membranous pouch-like proboscis is more clearly
seen beneath the breast, the extremity of which is directed
backward. In front of this organ there are two decurved
very mobile bristles, set on pedicles, the whole closely
resembling the internal antenna in the higher Crustacea.
The lateral horns or external antennas appear to terminate



BARNACLES 229

in a very delicate brush of hairs, which does not seem to
be protrusile.

The little animals in this state swim, generally, back
downward; though they frequently assume a perpendicular
position, both direct and reversed. I see them now oc-
casionally 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 this 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 downward, 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-
tions. The under surface of the body is also much corru-
gated 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 in statu quo.

We cannot follow the metamorphosis any further by
personal observation, 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 at-
tained. As yet no appreciable 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,



230 EVENINGS AT THE MICROSCOPE

toward the sessile Barnacle enclosed 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



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