JUNE AND JULY.
Lindia Torulosa--OEcistes Crystallinus--A professor of
deportment on stilts--Philodina--Changes of form and
habits--Structure of Gizzard in Philodina family--Mr. Gosse's
description--Motions of Rotifers--Indications of a will--Remarks
on the motions of lower creatures--Various theories--Possibility
of reason--Reflex actions Brain of insects--Consensual
actions--Applications of physiological reasoning to the
movements of Rotifers and Animalcules.
A Pressure of other occupations prevented full use being made of June
and July, nor was the weather at all propitious. For this reason the
microscopic doings of these two months are recorded in one chapter.
As usual the Kentish Town ponds were productive of objects, and among
them were several rotifers not found in the previous months. The first
of these was a very small worm-like thing, with one eye, a tuft of cilia
about the mouth, and two toes at the tail end. Had it not been for the
jaws, which were working like fingers thrust against each other, and
which were unmistakably of the rotifer pattern, the animal might have
been supposed to belong to some other class. According to the
'Micrographic Dictionary,' the _Lindia torulosa_ is 1--75" long, but
this specimen was only about 1--200". It was possibly very young, and
did not thrust out its cilia in two distinct tufts, as Cohn describes,
although it may have had the power of doing so. At times it sprang
quickly backwards and forwards, bringing its head where its tail was
before. This object required for its comfortable elucidation a power of
about six hundred linear.
[Illustration: OEcistes crystallinus.]
Among the common water-plants, which are worth examining as the probable
abodes of rotifers or infusoria, is the pretty little thing called
"star-weed," some of which was obtained from the last-mentioned ponds,
and on examination yielded a specimen of a tube-dwelling rotifer, the
_OEcistes crystallinus_, which, although less beautiful than the
Floscules or the Melicerta, is, nevertheless, a pretty and interesting
object. In this instance a little rough dirty tube, about 1--70" long,
was observed to contain an animal capable of rising up and expanding a
round mouth garnished with a wreath of cilia; while a little below, the
indefatigable and characteristic gizzard of the tribe was in full play.
A power of two hundred and forty linear sufficed to afford a good view,
and it was seen that a long, irregular, conical body was supported upon
a short wrinkled stalk. The usual drawings represent this creature with
a short bell-shaped body upon a very long slender pedicle. Possibly this
one might have been able to show himself under this guise, but he did
not attempt it; his appearance being always pretty much as described,
which made the foot shorter and the body longer than the measurements
which naturalists have given, and according to which the whole creature
is 1--36" long, although the body is only 1--140". The tube of the
_OEcistes_ is called a "lorica," or carapace; but it has in truth no
right whatever to the appellation.
Another strange rotifer, of whose name I am uncertain, had an ovalish
oblong body, and a pair of legs like compasses, twice as long as
himself. His antics were those of a posture-master, or "Professor of
Deportment" on stilts. Sometimes he stood bolt upright, bringing his
legs close together; then they were jauntily crossed, and the body
carried horizontally; then the two legs would be slightly opened, and
the body thrown exactly at right-angles to them. These antics were
repeated all the while the observation lasted, and had a very funny
effect in proving that drollery is practised, if not understood, in the
rotatorial world.
[Illustration: Philodina (swimming).]
Another kind of rotifer was abundant--the _Philodina_, which belongs to
the same family as the common wheel-bearer, namely, the _Philodinaea_.
The _Philodina_ is a good deal like the common wheel-bearer, or _Rotifer
vulgaris_, but is usually of a stouter build, and carries his eyes in a
different place. In the common rotifer these organs are situated on the
proboscis, while those of the Philodina are lower, and said to be
"cervical." The changes of form in this rotifer are still more
remarkable than in the common wheel-bearer. When resting it resembles a
pear-shaped purse, puckered in at the mouth. Then it thrusts out its
tail-foot, swells its body to an oval globe, protrudes its feeler, and
slightly exposes a row of cilia. After this two distinct wheels are
everted, and as their cilia whirl and spin, the animal is swiftly rowed
along, until it thinks proper to moor itself fast by the tail-foot, and
employ all its ciliary power in causing currents to converge towards its
throat. When it pleases it can elongate the body, till it becomes
vermiform, and it walks like the common rotifer, by curving its back,
and bringing its nose and its tail in contact with the ground.
[Illustration: Philodina (crawling).]
The gizzard of this family (_Philodinaea_) presents a considerable
deviation from the perfect form exhibited by the _Brachions_. According
to Mr. Gosse, "The _mallei_ and the _incus_ (terms already explained)
are soldered together into two subquadrantic-globular masses, which
appear to be muscular, but invested with a solid integument. The
_manubria_ (handles) may still be recognised in a vertical aspect as
three loops, of which the central one is chiefly developed, and in a
vertical aspect as a translucent reniform (kidney-shaped) globe." These
descriptions are not easy to understand, not from any want of clearness
or precision in the words employed, but from the complicated character
of the organ, and its very different appearance under different aspects.
To make the matter more intelligible, Mr. Gosse adds, "the structure and
action of an apparatus of this type may be made more clear by a homely
illustration. Suppose an apple to be divided longitudinally, leaving the
stalk attached to one half. Let this now be split again longitudinally
so far as the stalk, but not actually separating either portion from it.
Draw the two portions slightly apart, and lay them down on their rounded
surfaces. They now represent the quadrantic masses in repose, the stalk
being the fulcrum, and the upper surfaces being crossed by the teeth. By
the contraction of the muscles, of which they are composed, the two
segments are made to turn upon their long axis, until the points of the
teeth are brought into contact, and the toothed surfaces rise and
approach each other. The lower edges do not, however, separate as the
upper edges approach, but the form of the mass alters, becoming more
lenticular, so that when the toothed surfaces are brought into their
closest approximation, the outline has a subcircular figure. It is on
account of this change of form that I presume the masses themselves to
be partially composed of muscle."
These remarks, although specially made of the _Rotifer macrurus_, are in
the main applicable to all the Philodinas, but the student must not
expect to understand any of the complicated gizzards of the rotifers
without repeated observations, and no small exercise of patience. It is
common to call the portions of the Philodine-pattern gizzard
"stirrup-shaped," but Mr. Gosse has shown them to be _quadrantic_, that
is, shaped like the quarter of a sphere.
As we are not very well off with subjects for description in these two
months, we can afford a little time to consider a question that
continually arises in the mind, on viewing the movements of animalcules,
and especially of any so highly developed as the rotifers, namely, to
what extent motions which appear intelligent are really the result of
anything like a conscious purpose or will. When any of the lower
animals--a bee, for example--acts in precisely the same way as all bees
have acted since their proceedings have been observed, we settle the
question by the use of the term _instinct_. Those who take the lowest
view of insect life, assume that the bee flies because it has wings, but
without wishing to use them, and that the nerves exciting them to action
are in their turn excited, not by volition, but by some physical
stimulus.
The sight or the smell of flowers is thought by the same reasoners to be
capable of attracting the insect, which is unconscious of the
attraction, while proximity of food stimulates the tongue to make the
movements needful for its acquisition, and so forth. The cells, they
tell us, are built according to a pattern which the earliest bee was
impelled to construct by forces that bear no analogy to human reason and
human will, and so originate all the ordinary processes of bee life.
Sometimes, however, it happens that man or accident interposes
particular obstacles, and forthwith there appears a particular
modification of the orthodox plan, calculated to meet the special
difficulty. How is this? Does any one of the difficulties which the bee
or the ant is able to get over, produce precisely that kind of
electrical disturbance, or polar arrangement of nerve particles that is
necessary to stimulate the _first_ step of the action by which the
difficulty is surmounted; and does the new condition thus established
stimulate the _second_ step, and so forth, or can the bee, within
certain limits, really _think_, design, and contrive?
No questions are more difficult of solution; but while protesting
against a tendency to undervalue all life below that of man, we must
remember we have in our bodies processes going on which are not the
result of volition, as when the blood circulates, and its particles
arrange themselves in the pattern required to form our tissues and
organs, and also that many of our actions belong to the class termed by
physiologists, "reflex," that is, the result of external impressions
upon the nervous system, in which the _sentient_ brain takes no part.
Thus when a strong light stimulates the optic nerve, the portion of
brain with which it is connected in its turn stimulates the iris to
contract the pupil; and it is supposed that after a man has begun to
walk, through the exercise of his will, he may continue to walk, by a
reflex action; as his feet press the ground they transmit an impression
to the spinal cord, and the legs receive a fresh impulse to locomotion,
although the mind is completely occupied with other business, and pays
no attention to their proceedings.[14] The ordinary movements of insects
appear to be of this character, and to be excited by the ganglia
belonging to the segment to which the moving limbs are attached. Thus a
centipede will run, after its head has been cut off, and a water-beetle
(_Dytiscus_) swam energetically when thrown into water after its brain
had been removed.[15]
[14] See Carpenter's 'Manual of Physiology.'
[15] Carpenter's 'Manual of Physiology,' p. 551.
It must not, however, be assumed that the brain of insects has nothing
to do with their movements. It is probably the means of co-ordinating or
directing them to a common end, and gives rise to what are called
_consensual_ movements, that is, movements which are accompanied or
stimulated by a sensation, although not controlled by a will. In man
these actions are frequently exhibited, "as when laughter is provoked by
some ludicrous sight or sound, or by the remembrance of such at an
unseasonable hour."[16] Sneezing is another instance of a sensation
leading to certain motions, without any intervention of the human will.
[16] Ibid., p. 543.
Speaking of these consensual motions, Dr. Carpenter observes, "It is
probable, from the strong manifestations of emotion, exhibited by many
of the lower animals, that some of the actions which we assemble under
the general designation of instinctive are to be referred to this
group."
The insect brain is composed of a supra-oesophagal ganglion and
infra-oesophagal one. Von Siebold says, the first corresponds to the
cerebrum of the vertebrata, and "the second is comparable, perhaps, to
the cerebellum or spinal cord."[17] The superior ganglion gives off
nerves to the antennae and eyes, the lower one to the mandibles, &c. So
far as is known the insects that exhibit the most intelligence have the
largest and best developed brains.
[17] 'Anatomy of Invertebrates,' Burnett's trans.
A special volume would be required for anything like a complete
examination of the little which is known on this subject, but these few
remarks may assist the microscopic beginner in examining the movements
of his subjects, and guard against the error of referring to reason and
volition those which are, probably, either the direct result of
stimulants applied to the surface (as in nerveless creatures), or the
indirect (reflex) result of such stimulants in beings like the rotifers,
who have a nervous system; or the result of _sensations_, which excite
actions without previously referring the matter to the decision of a
will. It must not, however, be too readily assumed that the behaviour of
creatures possessing distinct organs is entirely automatic; and we must
not forget that even the best physiologists know very little concerning
the range of functions which the nervous ganglia of the invertebrata are
able to discharge.