Similar remarks are applicable to molluscs
and crustaceans; for again it is by way of procuring food that these
creatures take in water.
Aquatic in different ways, the differences depending on bodily
relation to external temperature and on habit of life, are such
animals on the one hand as take in air but live in water, and such
on the other hand as take in water and are furnished with gills but go
upon dry land and get their living there. At present only one animal
of the latter kind is known, the so-called cordylus or water-newt;
this creature is furnished not with lungs but with gills, but for
all that it is a quadruped and fitted for walking on dry land.
In the case of all these animals their nature appears in some
kind of a way to have got warped, just as some male animals get to
resemble the female, and some female animals the male. The fact is
that animals, if they be subjected to a modification in minute organs,
are liable to immense modifications in their general configuration.
This phenomenon may be observed in the case of gelded animals: only
a minute organ of the animal is mutilated, and the creature passes
from the male to the female form.
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