Philip Henry Gosse.

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ternate 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 a while we see nothing else: we can-
not 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
processes 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 toward each other.

Between the two middle spines the shell is cut into
a deep notch, out of which protrudes, when the wheels



260 EVENINGS AT THE MICROSCOPE

are expanded, a curious little organ, consisting of a couple
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 antennae 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 trans-
verse wrinkles, and its little fingers at the tip, so like an
elephant's trunk in miniature? This is the creature's
foot; the only one he has; and as I said the little tubu-
lar telescope represents the two antennae 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 philosophically, one of the pairs, the rest being ob-
solete. It must not be considered as a tail, not only from
its function, which is decidedly that of locomotion, but
also from its position on the ventral side of the intestinal
orifice. It is a curious organ, capable of great elongation
or, at the will of the animal, of entire retraction within
the abdomen; and this in an instant: while, as you ob-
served, 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 in-
sertions 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 sepa-



WHEELr-BEARERS 261

rated or brought into contact, at pleasure. 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 violence, as if irritated, yet without letting go
its foothold.

While thus anchored, the action of the ciliary 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 color-
ing matter with the water in which the animal is. I take
a little carmine with a wetted hair-pencil, as if I were go-
ing to color 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 refind 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
vigorously in the midst of them. They describe two
great circles, concentrical with the two wheels of 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 pro-
duces circular currents, into which every floating atom
within a certain distance is drawn, and in which it then



262 EVENINGS AT THE MICROSCOPE

continues to whirl round with a rapidity which increases
as it approaches the centre of rotation.

But the Brachionus suddenly lets go its foothold, and
a surprising change takes place. No 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? 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? Oh, yes; the successive strokes of his 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 pro-
portionate to the vigor 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 the fixed body (or nearly such), and the force of the
impact is mainly spent on the movable boat.

The Brachionus is the boat, its cilia are the oars, and
its foot is the rope. As long as this last maintains its



WHEEL^BEARERS 263

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 forward.

The use of the cilia in this latter case is obvious.
They enable the little animal to rove about at its way-
ward will; and doubtless motion is as pleasant and neces-
sary to it as to the fish in the sea or 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?

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, which are so vigor-
ously circling around 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 a 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



264 EVENINGS AT THE MICROSCOPE

atoms are thus arrested by these cilia, and are hurled by
their vibrations down this gulf. Yet not all, nor nearly
all; for the lips appear to possess the sense of taste, OP
of some modification of touch, which enables them to re-
fuse or 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 ani-
mals is to watch the swallowing of colored food, its re-
ception 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 secre-
tions, into the stomach, where other glands, answering to
a liver, change it, and thence into the intestine and rec-
tum, until its indigestible portion is discharged through
the cloacal orifice.

The object of the mingling of color with the water ia
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 colored pellet is everywhere recognizable, since it re-
tains its form and hue under all its changes, clearly re-
vealing 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, losing its own definite outline.

Let me now direct your attention to the organs de-
voted to the seizing and mastication of the food. And
the more because the form of these organs in the Hotifera
is quite peculiar quite unlike what is found in any other



WHEEL-BEARERS



265_



class of animals, though the parts are essentially the same
as those which we have already seen as entering into the
mouth in Insects.

Eemoving 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
mulberry-like clusters of that beautiful green creature,
Syncrypta voluox, which is now pretty generally consid-
ered a plant, though from its spontaneous motion, swim-
ming evenly along, revolving on
its axis as it goes, you would be
inclined to agree with earlier
observers in thinking it an ani-
mal. These appear to be fa-
vorite morsels with the Brachion:
one has already been devoured,
and is quite visible in the ali-
mentary canal, its brilliant green
hue shining out through the
translucent viscera and tissues.
Others are approaching, and two
or three are just now drawn into
the vortex of the ciliary current.
It is amusing to see the manoeu-
vres which the Brachionus makes
to take his prey. I say manoeu-
vres, for there really seem to be
perception and intelligence. The mode in which it directs
its ciliated naps toward the spot where a Syncrypta is
whirling, or suddenly stretches forward to the extent of
a long foot, as if it would seize the prey by force, seems

to indicate a cognizance of its proximity; as do also, still
15 SCIENCE 12




BRACHIONUS.



266 EVENINGS AT THE MICROSCOPE

more, the manner in which, it depresses the lip -like lobe
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 mul-
berry drops at length into the throat.

But now comes the tug of war; the black, millstone-
like jaws open wide and stretch forward to grasp the lit-
tle victim (which is still distinctly visible through the
transparent 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 expanse of the jaws being not quite sufficient to em-
brace it.

At last the little animal becomes indignant; the jaws
no more endeavor 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 Brach-
ion 's hunting; for a smaller globe has sunk into the
throat, and passes with a gulp into the mouth, between
the gaping jaws, which instantly close upon it, and, work-
ing 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 de-
fined than before, slips through a narrow postern-gate,
along a short narrow alley, into the digesting stomach.



WHEEL-BEARERS -261

But what sort of a mouth is this? It is enclosed
within the tissues of the body, not very far from its
centre, so that no part of it conies into contact with the
external water, or even approaches any part of the super-
ficies 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 ven-
tral side where the passage which I have called the throat,
but which is more correctly desig-
nated the luccal funnel, enters.
Within this muscular bulb are
placed two bent organs like ham-
mers, called mallei, and a third
central table, called the incus. The
mallei approach each other dorsally,
while the incus is placed toward
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, con-
nected 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 slen-




MOUTH OF BRACHIONUS.



268 EVENINGS AT THE MICROSCOPE

der 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 con-
tact with that of its fellow, in a state of repose. The
uncus of each malleus falls into the concavity of its corre-
sponding ramus, and is fastened to it by a stout triangular
muscle, which allows some freedom of motion.

Many muscles are inserted into various parts of these
organs, and into the walls of the mastax, 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;
and the rami of the incus with the maxillae; while the
walls of the mastax with the two edges of its orifice corre-
spond 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 essentially the same
structure, in which it is placed at the front margin of the
body, from which the jaws can be freely protruded. The
difiiculty will seem less if you weigh the following con-
siderations:

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 ordina-



WHEEL-BEARERS 369

rily, 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 permanently enclosed,
analogy requires us to consider the condition as induced
by a similar inversion, but of permanent duration. If
we imagine the head of a soft- bodied Insect-larva retracted
to a great degree (as is done partially by many Dipterous
larvae), the skin of the thoracic segments would meet to-
gether in front, around a purse-like opening, which would
be the orifice of such a buccal funnel as exists in most
Rotif&ra. In the latter, it is the normal 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
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 enor-
mous brain, the nervous matter being in a very diffuse
condition; and that the ruby seated on it is an eye, con-
sisting of a crystalline lens, and a layer of crimson pig-
ment beneath it.

The oval bodies that you see attached to the hinder



270 EVENINGS AT THE MICROSCOPE

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 beside the former
two, so that we now see three. These eggs are generally
carried by the parent until the young are hatched. The
oldest of these three is nearly ready for hatching, and if
you watch a while you will see the birth of the young.
At first exclusion, the egg which was seen some time be-
fore 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,
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 fitful con-
tractions and turnings take place. Soon an undefined
spot of red appears, which gradually acquires depth of
tint and a definite form, and we recognize 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 way of practice, for it is hard
to imagine what they can yet find to masticate.



WHEEIs-BEARERS 271

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 impa-
tiently 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 wheels of the infant Brach-
ion are seen rotating as perfectly as if the little creature
had had a yrr'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 hyaline, with no evidence of its
fracture, except a slight interruption of its outline, and a
very faint line running across.

This is a female young: the male is totally unlike the
female, and is very much smaller. We 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 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 Brachionw, and are ready to
cry ont "Ohel jam satis!" ' Well, then, I will turn him

1 "Oh dear 1 quite enough of this 1"



272 EVENINGS AT THE MICROSCOPE

off and show you another elegant little creature, the Whip-
tail (Mastigocerca carinata). I have here in a bottle some
stalks of the Water-Horsetail (Chara vulgaris), which I
obtained in 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 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 ad-
here 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 np the box perpendicularly,
not opposite the light, but obliquely, so that the field is
dark; but the light reflected and refracted by the animal-
cules 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 ex-
ample, 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 read-
ily put under the object-glass of the microscope. I have
found these leaves very productive of the more stationary
animalcules, the Hotifera especially.

It was in this way I this morning found the pretty and
delicate little Whiptail, which I am going to make the
subject of oar evening's study. It is enclosed 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



WHEEL-BEARERS

leans over considerably to the right side. Its basal por-
tion is hollow, and is continuous with the general cavity
of the shell, for we sometimes see portions of the viscera
in its interior.

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 Brack-




ionus, the Whiptail has a single horny spine of great slen-
derness, 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



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