Book IV

We have now treated, in regard to blooded animals of the parts
they have in common and of the parts peculiar to this genus or that,
and of the parts both composite and simple, whether without or within.
We now proceed to treat of animals devoid of blood. These animals
are divided into several genera.

One genus consists of so-called 'molluscs'; and by the term
'mollusc' we mean an animal that, being devoid of blood, has its
flesh-like substance outside, and any hard structure it may happen
to have, inside-in this respect resembling the red-blooded animals,
such as the genus of the cuttle-fish.

Another genus is that of the malacostraca. These are animals
that have their hard structure outside, and their soft or fleshlike
substance inside, and the hard substance belonging to them has to be
crushed rather than shattered; and to this genus belongs the
crawfish and the crab.