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INFUSORIA

over two opposite points of the brim. The cilia them-
selves cannot be distinguished, but their optical expres-
sion is curious. At the two opposite points of the circu-
lar margin, as seen in perspective when slightly inclined
toward the observer viz., at those points where the cilia,
from their position with regard to the eye, would be
crowded together there are seen two dark dashes, repre-
senting, doubtless, two ciliary waves, but which have all




VORTICBM^ffl!.



the appearance of tangible objects, sometimes withdrawn,
sometimes protruded, and often vibrating with a rapid
snatching movement.

These vases are of the usual appearance in Infusoria.
Their substance is the clear transparent colorless sarcode,
but it contains within it more or less of the cloudy neb-
ulous matter which we have been lately familiar with.
There are several globular vesicles or vacuoles, some
ready to imbibe color from pigment, and others already
occupied with brown food, while in each case we see,



452 EVENINGS AT THE MICROSCOPE

near the centre of the vase, a longish body of clear granu-
lar texture, which is called the nucleus, and which seems
to play an essential part in the vital economy of the
animal.

The movements of a group such as that we are looking
at are very sprightly and pleasing. The vases turned in
all directions, some presenting their mouths, some their
sides, some their bases to the eye; inclined at various
angles from the perpendicular, and bending in diverse
degrees upon the extremity of their stalks; swaying
slowly and gracefully to and fro, as driven hither and
thither by the ciliary currents, and, above all, ever flying
up and down within the length of their radius, as a bird
when confined by a string all these circumstances impart
a charm to this elegant animalcule which enables us to
look long at it without weariness.

This last movement is peculiar, and worthy of a mo-
ment's closer examination. The stalk, when extended to
the utmost, is an elastic glassy thread, nearly straight, like
a wire, but never so absolutely straight as not to show
slight undulations. The stalk when thus rendered tense
by extension is highly sensitive to vibrations in the sur-
rounding medium; and as, in the circumstances in which
we observe the animals, such vibrations must be every
instant communicated to the vessel in which they are
confined, the stalks are no sooner tense than they con-
tract with alarm. This depends on a contractile cord
which passes throughout the entire length of the stalk,
and which is distinctly visible in the larger species as a
narrow band. We can scarcely err in considering this
ribbon as a rudimentary condition of muscle, though we
do not recognize in it some of the characteristic con-



INFUSORIA 453

ditions in which we are accustomed to see it in higher
animals.

The contraction of the muscle is very sudden, ener-
getic, and complete. With a rapidity which the eye can-
not follow, the vase is brought down almost to the very
base of the stalk. Then it slowly rises again, and now we
see, what we could not discern in the act of contraction
itself, that in that act the stalk was thrown into an ele-
gant spiral of many turns, which at the utmost point of
contraction were packed close on each other, but which
in the extending act gradually separate, and at length
straighten their curves.

In any stage of the extension, the sudden contact of
the vase with any floating or fixed object apparently causes
alarm, and induces the vigorous contraction; but vibra-
tions, even when so violent as those produced by tapping
the stage of the microscope with the finger-nail, have no
effect unless the stalk be tense, its own power of vibra-
tion being then only developed, just as a cord becomes
musical in the ratio of its tension.

It is not until we view these creatures with a good mi-
croscope that we acquire an adequate idea of their beauty:
for myself, at least, it was so. I had seen engravings of
many of the invisible animalcules, and had read technical
descriptions ; but of their brilliant transparency, their sud-
den and sprightly motions, their general elegance and deli-
cacy, and the apparent intelligence with which they are
endowed, neither books nor engravings had given me any
conception.

Some of the individuals under our present examination
are exhibiting phenomena of no less interest than their
form and motions. Some of the stalks are terminated by



464 EVENINGS AT THE MICROSCOPE

two vases instead of one, which appear to spring from a
common point. These, however, are the result of the
spontaneous splitting of one; and in other examples you
may see the process in different stages, or, if your pa-
tience endure a couple of hours' watching, you may trace
the whole phenomena, as I have done, from the moment
when it first becomes recognizable to its completion in
the freedom of one of the newly formed animalcules.

For instance, you perceive that one of the bells, instead
of being vase-shaped, has assumed a globular form. By
keeping your eye on this for only a few moments, you
detect a depression forming in the midst of its front out-
line, which momentarily deepens, until it is manifestly a
cleft. The division proceeds downward, the two halves
healing simultaneously, so that they are at all times per-
fectly smooth and rounded; at length two vases appear,
side by side, where a few minutes before there had been
but one.

One of these is destined to be ultimately thrown off,
while the other retains sole possession of the stalk. You
goon see which it is that is going to emigrate: for though
the two are alike in size, the roving one early closes the
mouth of the vase, becoming smooth and globular there,
never to open again. The cilia, now therefore become
useless, disappear by absorption; but meanwhile a new
circle of these organs are developed around the basal ex-
tremity of the vase, and these, every instant becoming
more vigorous in their motions, sway the little globe
about on its point of attachment. At length the connec-
tion yields, breaks, and the animalcule shoots away, rowed
by its hundred oars, to find a new abode, and to found
a new colony.



INFUSORIA 455

Here and there you see shooting through the group,
with a rapid gliding movement, an oblong clear body.
This is one of the vases, formed by self-division, and exer-
cising its newly found power of locomotion. It is giddily
roving hither and thither, until the instinct of wandering
ceases, when it will soberly settle down, affix itself by the
point which was formerly its mouth, whence a new stalk
will gradually grow, and opening a new mouth in the
midst of the new crown of cilia.

I believe that the division is sometimes transverse in-
stead of longitudinal, the cleft occurring by constriction
across the middle of the vase; but this I have not seen.
In whatever direction it takes place, it is essential that the
oblong granular body, called the nucleus, which you see
in each vase, be divided, the cleft passing through the
middle of this substance, a portion of which is therefore
appropriated to each new-made animal.

That the essential vitality of the creature resides in this
nucleus is shown by another and highly curious mode of
increase; namely, that which is effected by encystion. Let
us search the live-box carefully, for amid so great a pro-
fusion of Vorticelloe as we have on this Nitella, it will go
hard if we do not find some individuals in the encysted
stage.

Look at this elegant object. It resembles a trumpet of
the clearest glass, with a rounded extremity, and with the
base affixed to the weed, from which it stands up erect.
Within the expanded part of the trumpet there is a turbid
mass, with a perfectly defined outline, from several points
of which proceed radiating pencils or tufts of long, straight,
stiff, elastic filaments, like threads of spun glass, varying
greatly in length, and each terminated by a little knob of



466 EVENINGS AT THE MICROSCOPE

the same material. The tout ensemble of this object is
very attractive and beautiful, and its history is a tale of
marvels.

No wonder that Ehrenberg, supposing this form to
be an independent animal, gave it a generic and specific
name. He called it Acineta mystacina. For who would




ACINETA.



have suspected that this stiff and motionless object, with
its tufts of flexible but inanimate threads, had any connec-
tion with the sprightly vases which we have been examin-
ing? Yet it is the same animalcule, in what we may,
with a certain liberty of phrase, call its chrysalis condi-
tion!



INFUSORIA 457

The history of the Vorticella, as it has been elaborately
worked out by Dr. Stein, exhibits phenomena analogous
to those marvellous changes which we lately considered
under the appellation of the Alternation of Generations.
Large individuals withdraw their circle of cilia, close up
the mouth, and become globular, and then secrete from
their whole surface a gummy substance, which hardens
into a spherical transparent shell, enclosing the Vorticella
in its cavity, in the form of a simple vesicle. Within this
vesicle is seen the band-shaped nucleus, unchanged, and
what was the contractile bladder, which, however, no
longer contracts.

By and by this torpid Vorticella enlarges itself ir-
regularly, pushing out its substance in tufts of threads,
and frequently protruding from one side a larger mass,
which becomes an adhering stalk. Thus it has become
an Acmeta, such as we now behold.

From this condition two widely different results may
proceed. In the one case, the encysted Vorticella sepa-
rates itself from the walls of the Acineta, and contracts into
an oval body, furnished at one end with a circle of vibra-
tory cilia, by whose movements it rotates vigorously in its
prison, while the more obtuse end is perforated by a
mouth leading into an internal cavity. In the interior of
this active oval body there are seen the band-like nucleus,
and a cavity which has again begun to contract and to
expand at regular intervals. It is, in fact, in every re-
spect like a Vorticella vase, which has just freed itself
from its stalk. Presently, the perpetual ciliary action so
far thins away the walls of the Acmeta that they burst at
some point or other, and the little Vorticella breaks out

of prison, and commences life afresh. The Acineta t mean-

SCIENCE 20



458 EVENINGS AT THE MICROSCOPE

while, soon heals its wound, and after a while develops a
new nucleus, which passes through the same stages as I
have described, and bursts out a second Vorticella.

But the cycle .of changes may be quite different from
this. For sometimes the nucleus within the Acineta, in-
stead of forming a Vorticella^ breaks itself up into a great
number of tiny clear bodies, resembling Monads, which
soon acquire independent motion, and glide rapidly about
the cell formed by the enclosed Vorticella-loody as in a
little sea. But by and by this body, together with the
Acineta wall, suddenly bursts, and the whole group of
Monad-like embryos are shot out, to the number of thirty
or upward. The Acineta now collapses and disappears,
having done its office, while the embryos shoot hither and
thither in newly acquired freedom. It is assumed, on
pretty good grounds, that these embryos soon become
fixed, develop stalks, which are at first not contractile,
and gradually grow into perfect Vorticellce, small at the
beginning, but capable of self-division, and of passing
into the Acineta stage, and gradually attaining the full
size of the race.

Some forms of the same family, Vorticelladce, are inter-
esting as dwelling in beautiful crystalline houses, of vari-
ous shapes, always elegant. All these have been ascer-
tained to pass through the same or similar Acineta stages.
Cothurnia imberbis is one of the prettiest of these. The
cell is of an elegant ampulla-like form, perfectly transpar-
ent and colorless, set on a stiff foot, or short pedicle,
which shows many transverse folds, like those of leather.
From the mouth of the vase projects the animal, whose
form may be distinctly traced through the clear walls of
the cell, attached to its bottom, whence it stretches up-



INFUSORIA 459

ward when seeking prey, or to which It shrinks when
alarmed.

In the former condition the body resembles a much
elongated Vorticella, with a similar circular orifice, set
round with cilia. Often the animal performs its ciliary
vibrations within the shelter of its house, not venturing
to protrude beyond its rim. If carmine be mixed with
the water, the atoms are seen in the customary vortex,
and some are occasionally drawn into the cell nearly half
way down its cavity, and then swiftly driven out again.
On a slight tap upon the table the animal withdraws, and
in the same moment the urn bends down upon its leath-
ery pedicle, at a point where there is always an angle, un-
til the rim of the cell is in contact with the plant to which
it is attached. This action is instantaneous. Presently,
however, it rises, and resumes its former position, and
then the mouth of the cell slowly opens, and the animal
again protrudes, the cilia appearing first, and finally the
head or front part of the animal, which is then opened
and begins to rotate.

Very similar to this are the Vaginicolm, but the cells
which they inhabit are not^ stalked, but are immovably
affixed to plants. In F. crystattina, the cell is a tall
goblet, standing erect, perfectly colorless; while in F.
decumbens, it is slipper-shaped, attached along its side,
and of a golden-brown hue, but still quite transparent.
Here is, fortunately, a group of the latter species, scat-
tered about the leaves of the Nitella.

Though, in general, both in form and habits, closely
like the Cothurnia, yet the Vaginicola has some peculiari-
ties of interest. The cilia are more developed, and can
be more distinctly seen than in either Cothurnia or Forti-



460 EVENINGS AT THE MICROSCOPE

cella, forming, when in swift action, a filmy ring above the
margin, along which, as if upon a wheel, one or more
dark points are frequently seen to run swiftly round; the
optical expression, as I presume, of a momentary slacken-
ing in the speed of the wave. The act of self -division
takes place in this animal, as in the Vorticellce; and it is
curious to see two Vaginicolce, exactly alike, lovingly in-
habiting the same cell. One of the cells which we are
now examining is in this doubly tenanted condition.

I will now exhibit to you some examples of the most
highly organized forms of this class of animals, in which




VAGINICOLA.



we discern a marked superiority over any that we have
yet looked at, and a distinct approach to those animals
whose more precise movements are performed by means
of special limbs. These creatures are excessively com-
mon, both in fresh and sea water, wherever vegetable mat-
ter is in process of ^decomposition; and hence their pres-
ence can at all times be commanded by keeping infusions.
In this old infusion of sage leaves, for instance, they occur
in vast multitudes, past all imagination; as you may see
with a lens in this drop.

This group belongs to the genus Stylonychia, and I
believe to the species S. pustulata. It presents the form



INFUSORIA 461

of an oval disk, which, when seen sidewise, is found to
be flat beneath and convex above. It commonly swims
with the belly upward, and when exhibited on the stage
of the microscope, in almost every case, this surface is
presented to the eye. ft darts about very irregularly, with
a bobbing motion, rarely going far in one direction, but
shooting a little distance, and then instantly receding,
turning short round, and starting hither and thither, so
fitfully that it is very difficult to obtain a fair sight of its
structure. Its margin, however, is surrounded by short
cilia; the mouth, which is a long opening on the front
part, and at the left side (as to the animal) of the ventral
surface, is fringed with long cilia, which are continually
vibrating. These are the organs of the darting motion;
but the creature crawls like a mouse, along the stems of
conferva, etc., which it performs by means of curved spines,
called uncini, near the front part, the points of which are
applied to the stem, and also by long stiff styles, or bris-
tles, which project backward and downward from the
hinder part. Sometimes the animalcules crawl for a mo-
ment back-downward, on the inner surface of the glass
cover, when the bases of the anterior curved spines appear
dilated like large spots. The spines are not capable of
much action, but they are rapidly used. The general
appearance of the creature reminds us of the little Wood-
louse or Armadillo of our gardens. The interior of the
body is occupied with a granular substance, in which are
scattered many globular vesicles of different sizes. The
animal is very transparent, and almost colorless. They
increase very fast by transverse division which is per-
formed under the microscope, so as greatly to increase the
number under examination even in an hour or two. A



462 EVENINGS AT THE MICROSCOPE

constriction forms in the middle of one, which quickly
deepens, dividing the oblong creature into two of circular
figure. The mouth of the new one, with its vibratile cilia,
is formed long before separation is complete, and at the
same end and side as in the parent. The styles and bris-
tles then form, and the creatures are held together for a
few seconds by these organs, even when the bodies are
distinctly severed. "When separated, they retain the round
form for some time.

When a drop of water is examined between two plates
of glass, it is amusing to observe the numbers that con-
gregate in the sinuosities left by the gradual drying of the
fluid. This probably becomes unfit for respiration, for
the motion of the cilia becomes more and more languid,
and the creatures die before the water is dry. They not
only die but vanish, so that where there were scores so
close that in moving they indented each other's sides and
crawled over one another if we look away for a few min-
utes, and again look, we see nothing but a few loose gran-
ules. This puzzled me, till I watched some dying, and I
found that each one burst and, as it were, dissolved. The
cilia moved up to the very last moment, especially the
strong ones in front, until, from some point in the outline,
the edge became invisible, and immediately the animal be-
came shapeless, and from the part which had dissolved
the interior parts seemed to escape, or rather the skin, so
to speak, seemed to dissolve, leaving only the loose
viscera. From the midst of these then pressed, as if by
the force of an elastic fluid within, several vesicles of a
pearly appearance, varying in number and size, and then
the whole became evanescent.

You will have observed that the admixture of carmine



INFUSORIA 463

to the water, while the animalcules were active, shows the
direction of the ciliary motion with great distinctness.
The particles form two vortices, one on each side of the
front, which meet in the centre in a strong current, and
pass off behind the mouth on each side. We do not per-
ceive that any of them swallow the particles of carmine,
for the internal vessels remain colorless.

I have found that, if a drop of water containing these
animals be placed on a slip of glass exposed to the open
air, they do not burst as the water dries away; but dry
fiat on the glass, their bodies broader, but shorter than
when alive, and quite entire. Their cilia are then very
manifest. On being again wetted, though after only a
few minutes' desiccation, I have never been able to re-
vive them, nor any other Infusoria in like circumstances,
notwithstanding what is stated in books.

Here is another species in equally amazing profusion,
jS. mytilus. Its form is oblong, with rounded extremities,
the anterior obliquely dilated. This species affords a good
example of the various organs of locomotion. A trans-
parent oblong shield, which is quite soft and flexible, is
spread over the back, which does not prevent the eye dis-
cerning all the organs through it, though much more com-
monly the animal, when under the microscope, crawls, belly
upward, beneath the glass cover of the live-box. Around
the anterior part, which is broadened, are placed cilia,
which are vibratile ; these are continued round the mouth,
a sort of fold on the side. Toward the posterior extremity
on each side are other rows of cilia, which being large are
well displayed. On the ventral surface, chiefly toward
the front part, are seen several thick pointed processes,
shaped like the prickles of a rose, but flexible, and capa-



464 EVENINGS AT THE MICROSCOPE

ble of being turned every way. These are the uncini, and
are evidently used as feet, the tips being applied to the
glass. The optical effect of the throwing about of these
unoini, when the place which they touch is in focus, is
very curious. They are rapidly moved, but without reg-
ularity; the tips bend as they touch the surface of the
glass; some of them seem to have accessory hairs, equally
long, but slender, proceeding from the same base. On the
hinder quarter of the ventral surface are several thick
pointed spines ; these are inflexible^ nearly straight, placed
side by side, but not in regular order, some reaching
beyond others. I have not seen these used, but they
commonly remain sticking out in a horizontal direction.
These organs are termed styles. Besides these, there are
three slender bristles, called setce, placed at the hinder
extremity, the central one in the line of the body, the
others radiating at an angle. These are distinguished
from the cilia not only by their length, but by not be-
ing vibratile. The motions of these animals are powerful,
but irregular and fitful, very much like those of the for-
mer species. They dart hither and thither, backward as
well as forward, occasionally shooting round and round in
a circle, with many gyrations, much like the pretty little
polished beetles (Gyrinus) that play in mazy dances on
the surface of a pool. The two extremities seem cov-
ered with minute pits or stipplings, but colorless; the
central part is occupied with yellowish granules of dif-
erent sizes.

I once witnessed the dissolution of one of these animals
under peculiar circumstances. Two or three stems of an
aquatic plant had become crossed in the live-box so as to
form an area, into which the 8tylonychia had somehow



INFUSORIA 465

introduced himself. There was just room for him to move
backward and forward without turning, and the space was
about three times his own length. Within this narrow
limit he impatiently continued crawling to and fro, mov-
ing his uncini with great rapidity and showing their ex-
treme flexibility, for as he applied them now to the stem,
now to the surface of the glass, these whip-like uncini
were sometimes bent double. The so-called styles at the
posterior extremity, though less frequently used so, were
yet occasionally bent and applied to the surface as feet,
so that they are certainly not inflexible as supposed, nor
do I see any essential difference between them and the
uncini. The whole body was flexible, taking the form of
any passage or nook into which it was thrust, yet recover-
ing its elasticity immediately the pressure was removed.
Its proper form appeared to be convex above and con-
cave beneath, rather than flat. After having been thus
employed about half an hour under my observation, it
became still, moving only its cilia, when I left it a little
while, and on my return found that it was dissolved; the
outline having entirely disappeared, and nothing being left
but the granules, and globular vesicles, that had consti-
tuted its viscera, some of which still contained the car-
mine which had been very perceptible in the living ani-
mal. This was the more remarkable, as there was plenty
of water. It looked like suicide, a spontaneous choosing of
death rather than hopeless captivity.

Common as these Stylonycliice are, and abundant be-
yond all calculation, where they do occur, from their
tendency to self-division, they are not so universally met
with as their cousins of the genus Euplotes. These are
still more highly organized, and will please you by their




466 EVENINGS AT THE MICROSCOPE

activity and sprightly intelligence, I am sure. Here are
several individuals in the live-box at this moment.

They differ from the Stylonychice, in having the soft
body covered with a plate of crystal mail, hard and in-



Online LibraryPhilip Henry GosseEvenings at the microscope (Volume 1) → online text (page 31 of 32)