by Aristotle
efficiently with the hinder part of the body. Polypterous insects,
on the other hand, are of greater bulk-indeed it is this which
causes them to have so many feathers; and their greater size makes
them stronger in their hinder parts. The sting of such insects is
therefore placed behind. Now it is better, when possible, that one and
the same instrument shall not be made to serve several dissimilar
uses; but that there shall be one organ to serve as a weapon, which
can then be very sharp, and a distinct one to serve as a tongue, which
can then be of spongy texture and fit to absorb nutriment. Whenever,
therefore, nature is able to provide two separate instruments for
two separate uses, without the one hampering the other, she does so,
instead of acting like a coppersmith who for cheapness makes a spit
and lampholder in one. It is only when this is impossible that she
uses one organ for several functions.
The anterior legs are in some cases longer than the others, that
they may serve to wipe away any foreign matter that may lodge on the
insect's eyes and obstruct its sight, which already is not very
distinct owing to the eyes being made of a hard substance. Flies and
bees and the like may be constantly seen thus dressing themselves with
crossed forelegs. Of the other legs, the hinder are bigger than the
middle pair, both to aid in running and also that the insect, when
it takes flight, may spring more easily from the ground. This
difference is still more marked in such insects as leap, in locusts
for instance, and in the various kinds of fleas. For these first
bend and then extend the legs, and, by doing so, are necessarily
shot up from the ground. It is only the. hind legs of locusts, and not
the front ones, that resemble the steering oars of a ship. For this
requires that the joint shall be deflected inwards, and such is
never the case with the anterior limbs. The whole number of legs,
including those used in leaping, is six in all these insects.
7
In the Testacea the body consists of but few parts, the reason being
that these animals live a stationary life. For such animals as move
much about must of necessity have more numerous parts than such as
remain quiet; for their activities are many, and the more
diversified the movements the greater the number of organs required to
effect them. Some species of Testacea are absolutely motionless, and
others not quite but nearly so. Nature, however, has provided them
with a protection in the hardness of the shell with which she has
invested their body. This shell, as already has been said, may have
one valve, or two valves, or be turbinate. In the latter case it may
be either spiral, as in whelks, or merely globular, as in sea-urchins.
When it has two valves, these may be gaping, as in scallops and
mussels, where the valves are united together on one side only, so
as to open and shut on the other; or they may be united together on
both sides, as in the Solens (razor-fishes). In all cases alike the
Testacea have, like plants, the head downwards. The reason for this
is, that they take in their nourishment from below, just as do
plants with their roots. Thus the under parts come in them to be
above, and the upper parts to be below. The body is enclosed in a
membrane, and through this the animal filters fluid free from salt and
absorbs its nutriment. In all there is a head; but none of the
parts, excepting this recipient of food, has any distinctive name.
8
All the Crustacea can crawl as well as swim, and accordingly they
are provided with numerous feet. There are four main genera, viz.
the Carabi, as they are called, the Astaci, the Carides, and the
Carcini. In each of these genera, again, there are numerous species,
which differ from each other not only as regards shape, but also
very considerably as regards size. For, while in some species the
individuals are large, in others they are excessively minute. The
Carcinoid and Caraboid Crustacea resemble each other in possessing
claws. These claws are not for locomotion, but to serve in place of
hands for seizing and holding objects; and they are therefore bent
in the opposite direction to the feet, being so twisted as to turn
their convexity towards the body, while their feet turn towards it
their concavity. For in this position the claws are best suited for
laying hold of the food and carrying it to the mouth. The
distinction between the Carabi and the Carcini (Crabs) consists in the
former having a tail while the latter have none. For the Carabi swim
about and a tail is therefore of use to them, serving for their
propulsion like the blade of an oar. But it would be of no use to
the Crabs; for these animals live habitually close to the shore, and
creep into holes and corners. In such of them as live out at sea,
the feet are much less adapted for locomotion than in the rest,
because they are little given to moving about but depend for
protection on their shell-like covering. The Maiae and the crabs known
as Heracleotic are examples of this; the legs in the former being very
thin, in the latter very short.
The very minute crabs that are found among the small fry at the
bottom of the net have their hindermost feet flattened out into the
semblance of fins or oar-blades, so as to help the animal in swimming.
The Carides are distinguished from the Carcinoid species by the
presence of a tail; and from the Caraboids by the absence of claws.
This is explained by their large number of feet, on which has been
expended the material for the growth of claws. Their feet again are
numerous to suit their mode of progression, which is mainly by
swimming.
Of the parts on the ventral surface, those near the head are in some
of these animals formed like gills, for the admission and discharge of
water; while the parts lower down differ in the two sexes. For in
the female Carabi these are more laminar than in the males, and in the
female crabs the flap is furnished with hairier appendages. This gives
ampler space for the disposal of the ova, which the females retain
in these parts instead of letting them go free, as do fishes and all
other oviparous animals. In the Carabi and in the Crabs the right claw
is invariably the larger and the stronger. For it is natural to
every animal in active operations to use the parts on its right side
in preference to those on its left; and nature, in distributing the
organs, invariably assigns each, either exclusively or in a more
perfect condition, to such animals as can use it. So it is with tusks,
and teeth, and horns, and spurs, and all such defensive and
offensive weapons.
In the Lobsters alone it is a matter of chance which claw is the
larger, and this in either sex. Claws they must have, because they
belong to a genus in which this is a constant character; but they have
them in this indeterminate way, owing to imperfect formation and to
their not using them for their natural purpose, but for locomotion.
their position and their differences, those parts being also
included which distinguish the sexes, reference must be made to the
treatises on Anatomy and to the Researches concerning Animals.
9
We come now to the Cephalopoda. Their internal organs have already
been described with those of other animals. Externally there is the
trunk of the body, not distinctly defined, and in front of this the
head surrounded by feet, which form a circle about the mouth and
teeth, and are set between these and the eyes. Now in all other
animals the feet, if there are any, are disposed in one of two ways;
either before and behind or along the sides, the latter being the plan
in such of them, for instance, as are bloodless and have numerous
feet. But in the Cephalopoda there is a peculiar arrangement,
different from either of these. For their feet are all placed at
what may be called the fore end. The reason for this is that the
hind part of their body has been drawn up close to the fore part, as
is also the case in the turbinated Testacea. For the Testacea, while
in some points they resemble the Crustacea, in others resemble the
Cephalopoda. Their earthy matter is on the outside, and their fleshy
substance within. So far they are like the Crustacea. But the
general plan of their body is that of the Cephalopoda; and, though
this is true in a certain degree of all the Testacea, it is more
especially true of those turbinated species that have a spiral
shell. Of this general plan, common to the two, we will speak
presently. But let us first consider the case of quadrupeds and of
man, where the arrangement is that of a straight line. Let A at the
upper end of such a line be supposed to represent the mouth, then B
the gullet, and C the stomach, and the intestine to run from this C to
the excremental vent where D is inscribed. Such is the plan in
sanguineous animals; and round this straight line as an axis are
disposed the head and so-called trunk; the remaining parts, such as
the anterior and posterior limbs, having been superadded by nature,
merely to minister to these and for locomotion.
In the Crustacea also and in Insects there is a tendency to a
similar arrangement of the internal parts in a straight line; the
distinction between these groups and the sanguineous animals depending
on differences of the external organs which minister to locomotion.
But the Cephalopoda and the turbinated Testacea have in common an
arrangement which stands in contrast with this. For here the two
extremities are brought together by a curve, as if one were to bend
the straight line marked E until D came close to Such, then, is the
disposition of the internal parts; and round these, in the
Cephalopoda, is placed the sac (in the Poulps alone called a head),
and, in the Testacea, the turbinate shell which corresponds to the
sac. There is, in fact, only this difference between them, that the
investing substance of the Cephalopoda is soft while the shell of
the Testacea is hard, nature having surrounded their fleshy part
with this hard coating as a protection because of their limited
power of locomotion. In both classes, owing to this arrangement of the
internal organs, the excrement is voided near the mouth; at a point
below this orifice in the Cephalopoda, and in the Turbinata on one
side of it.
Such, then, is the explanation of the position of the feet in the
Cephalopoda, and of the contrast they present to other animals in this
matter. The arrangement, however, in the Sepias and the Calamaries
is not precisely the same as in the Poulps, owing to the former
having no other mode of progression than by swimming, while the latter
not only swim but crawl. For in the former six of the feet are above
the teeth and small, the outer one on either side being the biggest;
while the remaining two, which make up the total weight, are below the
mouth and are the biggest of all, just as the hind limbs in quadrupeds
are stronger than the fore limbs. For it is these that have to support
the weight, and to take the main part in locomotion. And the outer two
of the upper six are bigger than the pair which intervene between them
and the uppermost of all, because they have to assist the lowermost
pair in their office. In the Poulps, on the other hand, the four
central feet are the biggest. Again, though the number of feet is
the same in all the Cephalopoda, namely eight, their length varies
in different kinds, being short in the Sepias and the Calamaries,
but greater in the Poulps. For in these latter the trunk of the body
is of small bulk, while in the former it is of considerable size;
and so in the one case nature has used the materials subtracted from
the body to give length to the feet, while in the other she has
acted in precisely the opposite way, and has given to the growth of
the body what she has first taken from the feet. The Poulps, then,
owing to the length of their feet, can not only swim but crawl,
whereas in the other genera the feet are useless for the latter mode
of progression, being small while the bulk of the body is
considerable. These short feet would not enable their possessors to
cling to the rocks and keep themselves from being torn off by the
waves when these run high in times of storm; neither would they
serve to lay hold of objects at all remote and bring them in; but,
to supply these defects, the animal is furnished with two long
proboscises, by which it can moor itself and ride at anchor like a
ship in rough weather. These same processes serve also to catch prey
at a distance and to bring it to the mouth. They are so used by both
the Sepias and the Calamaries. In the Poulps the feet are themselves
able to perform these offices, and there are consequently no
proboscises. Proboscises and twining tentacles, with acetabula set
upon them, act in the same way and have the same structure as those
plaited instruments which were used by physicians of old to reduce
dislocations of the fingers. Like these they are made by the
interlacing of their fibres, and they act by pulling upon pieces of
flesh and yielding substances. For the plaited fibres encircle an
object in a slackened condition, and when they are put on the
stretch they grasp and cling tightly to whatever it may be that is
in contact with their inner surface. Since, then, the Cephalopoda have
no other instruments with which to convey anything to themselves
from without, than either twining tentacles, as in some species, or
proboscises as in others, they are provided with these to serve as
hands for offence and defence and other necessary uses.
The acetabula are set in double line in all the Cephalopoda
excepting in one kind of poulp, where there is but a single row. The
length and the slimness which is part of the nature of this kind of
poulp explain the exception. For a narrow space cannot possibly
admit of more than a single row. This exceptional character, th
en,
belongs to them, not because it is the most advantageous
arrangement, but because it is the necessary consequence of their
essential specific constitution.
In all these animals there is a fin, encircling the sac. In the
Poulps and the Sepias this fin is unbroken and continuous, as is
also the case in the larger calamaries known as Teuthi. But in the
smaller kind, called Teuthides, the fin is not only broader than in
the Sepias and the Poulps, where it is very narrow, but, moreover,
does not encircle the entire sac, but only begins in the middle of the
side. The use of this fin is to enable the animal to swim, and also to
direct its course. It acts, that is, like the rump-feathers in
birds, or the tail-fin in fishes. In none is it so small or so
indistinct as in the Poulps. For in these the body is of small bulk
and can be steered by the feet sufficiently well without other
assistance.
The Insects, the Crustacea, the Testacea, and the Cephalopoda,
have now been dealt with in turn; and their parts have been described,
whether internal or external.
10
We must now go back to the animals that have blood, and consider
such of their parts, already enumerated, as were before passed over.
We will take the viviparous animals first, and, we have done with
these, will pass on to the oviparous, and treat of them in like
manner.
The parts that border on the head, and on what is known as the
neck and throat, have already been taken into consideration. All
animals that have blood have a head; whereas in some bloodless
animals, such as crabs, the part which represents a head is not
clearly defined. As to the neck, it is present in all the Vivipara,
but only in some of the Ovipara; for while those that have a lung also
have a neck, those that do not inhale the outer air have none. The
head exists mainly for the sake of the brain. For every animal that
has blood must of necessity have a brain; and must, moreover, for
reasons already given, have it placed in an opposite region to the