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History of Animals   

side of the head, where the animal discharges its residuum; and this
holds good in the case of all stromboid testaceans, whether
terrestrial or marine. From the stomach there is drawn in a parallel
direction with the oesophagus, in the larger snails, a long white duct
enveloped in a membrane, resembling in colour the mastoid formations
higher up; and in it are nicks or interruptions, as in the egg-mass of
the crawfish, only, by the way, the duct of which we are treating is
white and the egg-mass of the crawfish is red. This formation has no
outlet nor duct, but is enveloped in a thin membrane with a narrow
cavity in its interior. And from the gut downward extend black and
rough formations, in close connexion, something like the formations in
the tortoise, only not so black. Marine snails, also, have these
formations, and the white ones, only that the formations are smaller
in the smaller species.
The non-spiral univalves and bivalves are in some respect
similar in construction, and in some respects dissimilar, to the
spiral testaceans. They all have a head and horns, and a mouth, and
the organ resembling a tongue; but these organs, in the smaller
species, are indiscernible owing to the minuteness of these animals,
and some are indiscernible even in the larger species when dead, or
when at rest and motionless. They all have the mecon, or poppy, but
not all in the same place, nor of equal size, nor similarly open to
observation; thus, the limpets have this organ deep down in the bottom
of the shell, and the bivalves at the hinge connecting the two valves.
They also have in all cases the hairy growths or beards, in a circular
form, as in the scallops. And, with regard to the so-called 'egg',
in those that have it, when they have it, it is situated in one of the
semi-circles of the periphery, as is the case with the white formation
in the snail; for this white formation in the snail corresponds to the
so-called egg of which we are speaking. But all these organs, as has
been stated, are distinctly traceable in the larger species, while
in the small ones they are in some cases almost, and in others
altogether, indiscernible. Hence they are most plainly visible in
the large scallops; and these are the bivalves that have one valve
flat-shaped, like the lid of a pot. The outlet of the excretion is
in all these animals (save for the exception to be afterwards related)
on one side; for there is a passage whereby the excretion passes
out. (And, remember, the mecon or poppy, as has been stated, is an
excretion in all these animals-an excretion enveloped in a
membrane.) The so-called egg has no outlet in any of these
creatures, but is merely an excrescence in the fleshy mass; and it
is not situated in the same region with the gut, but the 'egg' is
situated on the right-hand side and the gut on the left. Such are
the relations of the anal vent in most of these animals; but in the
case of the wild limpet (called by some the 'sea-ear'), the residuum
issues beneath the shell, for the shell is perforated to give an
outlet. In this particular limpet the stomach is seen coming after the
mouth, and the egg-shaped formations are discernible. But for the
relative positions of these parts you are referred to my Treatise on
The so-called carcinium or hermit crab is in a way intermediate
between the crustaceans and the testaceans. In its nature it resembles
the crawfish kind, and it is born simple of itself, but by its habit
of introducing itself into a shell and living there it resembles the
testaceans, and so appears to partake of the characters of both kinds.
In shape, to give a simple illustration, it resembles a spider, only
that the part below the head and thorax is larger in this creature
than in the spider. It has two thin red horns, and underneath these
horns two long eyes, not retreating inwards, nor turning sideways like
the eyes of the crab, but protruding straight out; and underneath
these eyes the mouth, and round about the mouth several hair-like
growths, and next after these two bifurcate legs or claws, whereby
it draws in objects towards itself, and two other legs on either side,
and a third small one. All below the thorax is soft, and when opened

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