All crustaceans

take in water close by the mouth. The crab
discharges it, closing up, as it does so, a small portion of the same,
and the crawfish discharges it by way of the gills; and, by the way,
the gill-shaped organs in the crawfish are very numerous.

The following properties are common to all crustaceans: they
have in all cases two teeth, or mandibles (for the front teeth in
the crawfish are two in number), and in all cases there is in the
mouth a small fleshy structure serving for a tongue; and the stomach
is close to the mouth, only that the crawfish has a little
oesophagus in front of the stomach, and there is a straight gut
attached to it. This gut, in the crawfish and its congeners, and in
the carids, extends in a straight line to the tail, and terminates
where the animal discharges the residuum, and where the female
deposits her spawn; in the crab it terminates where the flap is
situated, and in the centre of the flap. (And by the way, in all these
animals the spawn is deposited outside.) Further, the female has the
place for the spawn running along the gut. And, again, all these
animals have, more or less, an organ termed the 'mytis', or
'poppyjuice'.