Philip Henry Gosse.

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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 in-
serted 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.



274 EVENINGS AT THE MICROSCOPE

The most remarkable circumstance connected with this
elegant little animal is the unusual form of the dental ap-
paratus, which differs so immensely from that of Brack-
ionus that we should never recognize them as being
the same organs, if we had not numerous intermediate
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 ir-
regularly 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 an-
gles greatly produced. The mallei have long, slender,
incurved manubria, and simple unci.

But the remarkable circumstance is the non-symmet-
rical 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 dilated into an expansion, with several
irregular 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, com-
bined with the unsymmetrical character of the dorsal ridge,
of the foot-spine, and of some other organs, render this
genus ft highly curious one to the naturalist.

The little Whiptail is as lively in its motions as it is



WHEEL-BEARERS 275 -

elegant in its form. When swimming, it glides with con-
siderable swiftness through the water, turning frequently
on its course, and often partially revolving on its long
axis. When enclosed, as is often the case, by two frag-
ments of the filamentous Chara, it travels along the sides
of its enclosure, nibbling, as it goes, the floccose 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 Brachionus, nor is it so much used as a support
or turning point. 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 Rotifera by transmitted
light, and their crystalline transparency renders them beau-
tiful objects when thus exhibited. But we will now look
at the Whiptail by the direct light of the sun upon it, con-
densed, 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 colorless as a vase of glass, but re-
flects the rays brightly from its polished surface. An ad-
vancing egg in the ovary is opaque white, as is the front
part of the mastax; the stomach and intestine filled 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 Cftara-jar, 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. Now then for the examination.



276



EVENINGS AT THE MICROSCOPE



Ha! here is the curious Skeleton Wheel-bearer Dinocharis
pocillum nay, several of them.

This genus is remarkable for possessing true joints in
the foot; not merely telescopic inversions of the skin, but
permanent articulations with swollen condyles, resembling
those of the antennae of a beetle. Hence the Skeleton has




SKELETON WHEEL-BEARER.



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 remarkable agility.
These joints admit of forward and lateral flexure, but you
never see the body brought backward beyond a perpen-
dicular position, the swelling of the terminal portion of
each articulation precluding further motion in that direc-



WHEEL-BEARERS 277

tion; 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 with-
drawn, 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 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 convo-
luted threads that are believed to be connected with res-
piration, within the lateral wings. The stomachs are gen-



278 EVENINGS AT THE MICROSCOPE

erally full of green and brown food, but they will not
imbibe carmine.

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 individ-
uals as to their length, slenderness, and direction; some-
times being quite short, at others as long as the toes;
generally, they arch downward, but occasionally they
stand out straight, or even curve upward. In some speci-
mens these 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 ap-
parent 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 irreg-
ularity 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
expanded pair of compasses, and sometimes the joints of
the foot are suddenly bent in zig-zag fashion, and then
as abruptly straightened. The animal swims gracefully,
but only with moderate swiftness, the rotatory crown of
cilia being 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-



WHEEL-BEARERS 279

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 see the remains of de-
funct specimens the skeleton of the Skeleton; this itself
makes a pretty object: the lorica, with its points and
ridges, the thoracic column, the foot with its joints and
spines, and the toes, being perfectly preserved, and ren-
dered even more clear than during life, because of the re-
moval of all 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 mo-
tion and irregular leaps, and partly on account of its ex-
treme 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 backward or
to one side, and that so quickly that the eye often cannot
follow it in the transition. The organs by which these



280 EVENINGS AT THE MICROSCOPE

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 performs them, after
a momentary examination of any floating matter with
which its course brings it into contact.

The rotatory organs, the source of the common glid-
ing motion, are not very large or conspicuous; the cilia
appear to be set all along the brow. The eye is very
noticeable: it is placed near the front and seems to be of
a deep bluish-black hue.

1 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 mi-
nute forms has placed the species among those which are
destitute of a horny lorica or shell. But he is certainly
in error here, for, as you may see, there is manifestly 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, however, 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,



WHEEL-BEARERS 28 J^

arranged 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 ordi-
narily count; but I have seen more: one day, while ex-
amining a specimen that presented a vertical aspect to me
end-on, to speak familiarly the fins being all expanded,
I saw with perfect distinctness a seventh pair, proceeding
from the middle of the breast. They are flat, thin, nar-
row 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 doubt-
less 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 antennas,
each bearing a pencil of very fine bristles. And just
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 toward the ventral aspect, there is a huge mastax,
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 perseverance and
skill in manipulation to resolve them. They were an
enigma to me for years.

The great mastax is pear-shaped, pointing obliquely



282



EVENINGS AT THE MICROSCOPE



toward the middle of the belly. This form is owing to
the great length of the fulcrum, and the wide curvature
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
not protruded from the front; their whole 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




SWORD-BEAKER.



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
impossible 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



WHEEZE-BEARERS



283



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 vesi-
culosum), which very frequently infest this species, adher-
ing to various points of the shell, and even to the sword-
fins.

What I have now to 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 Neptunius). 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 crea-
ture 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
posterior one. Those in front terminate in an oval probos-
cis, which having a sort of finger at its extremity, and two
eyes, with an antennal tube projecting obliquely backward,
presents, when viewed laterally, a strong resemblance 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




TRIPOD WHEEL-BEARES.



284 EVENINGS AT THE MICROSCOPE

the last example, a red of great intensity. When the head
is withdrawn, the integument is very clearly seen to be in-
troverted. The body consists of one long cylindrical tube,
which receives three or four short joints to complete the
abdomen; at the dorsal aspect of the extremity of the last
of these is the cloaca ; at this point 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. Toward 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 commonly bent outward; they are equal
in thickness, and truncate. These are often retracted in
various degrees, even when the foot is otherwise ex-
tended.

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 mas-
tax, with, I think, two small basal glands; its posterior
extremity becomes gradually tapered to the cloaca. In the
specimen we are examining, a small quantity of fecal matter
of a yellowish-brown color is collected in two small masses,
near the extremity. Along the ventral aspect runs the
ovary, which in this specimen contains two long oval eggs
in advanced development; from their transparent bright-
ness, I suspect the young are produced before birth. I
think I can detect a contractile bladder, but am not certain.



WHEEL-BEARERS 285

The dorsal region of the trunk is marked with strong
rugged lines running longitudinally; these look like cor-
rugations 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 demonstrated 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 had 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 with-
drawn within the body ; in which state the resemblance to
a telescope, or to a nest of glass-tubes, is striking).

The last specimen of this class of tiny favorites that I
shall show you is one of more than ordinary beauty. It
is the Two -lipped Tube -wheel of the Horn wort (Limnias



286 EVENINGS AT THE MICROSCOPE

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 Horn wort
(Ceratophyllum demersum)^ that grows commonly in slug-
gish streams and pasture-pools, is a favorite 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 Crowfoot (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 sur-
face, 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 direc-
tions from the surface of the leaves. The colony is rather
numerous in this case, and we shall have no difficulty in
selecting our specimens.

On this filament, which I have seized with the points 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.



WHEEL-BEARERS



287



slightly widening at the mouth, is affixed by the lower
extremity to the slender filaments of water-grass, crow-
foot, etc. It is about one fifty-fifth of an inch in length,
pellucid but tinged with brownish yellow. It appears to
be of a gelatinous texture, and is covered with extraneous
substances, such as decaying animal or vegetable matters,
which adhere to its surface. From the mouth of the tube
protrudes a transparent colorless animal, the
head of which is rounded, with the extrem-
ity 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 resem-
bling 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 sinu-
osity, on the opposite sides, and around the
margin again, is very striking. The cilia at
the front are interrupted between the lobes.
In the centre of each lobe is a broad plate,

111 , . -I - .. TWO-LIFPED TUBE*-

surrounded by a bright nng, and crossed WHEEL.
by radiating lines which also extend toward the ciliated
margin; probably these are muscular filaments. The fun-
nel is between the lobes, and leads by a short oesophagus
to a bulbous transparent mastax, in which are seen jaws
that work 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 up-
ward through the whole length, terminating in an orifice




288 EVENINGS AT THE MICROSCOPE

behind the rotatory organ ; for though I have not traced it
when empty, I have seen the fecal 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




WHEELS OF TUBE-WHEEL.



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



Online LibraryPhilip Henry GosseEvenings at the microscope (Volume 1) → online text (page 19 of 32)