Книга только для ознакомления
. The degree of distinctness, however, with which they are
formed varies in the different kinds, and the larger the size of the
animal the more easily distinguishable are all these parts
severally. In the Sea-snails, for example, we find teeth, hard and
sharp, as before mentioned, and between them the flesh-like substance,
just as in the Crustacea and Cephalopoda, and again the proboscis,
which, as has been stated, is something between a sting and a
tongue. Directly after the mouth comes a kind of bird-like crop,
then a gullet, succeeded by a stomach, in which is the mecon, as it is
styled; and continuous with this mecon is an intestine, starting
directly from it. It is this residual substance which appears in all
the Testacea to form the most palatable morsel. Purpuras and Whelks,
and all other Testacea that have turbinate shells, in structure
resemble the Sea-snail. The genera and species of Testacea are very
numerous. For there are those with turbinate shells, of which some
have just been mentioned; and, besides these, there are bivalves and
univalves. Those with turbinate shells may, indeed, after a certain
fashion be said to resemble bivalves. For they all from their very
birth have an operculum to protect that part of their body which is
exposed to view. This is the case with the Purpuras, with Whelks, with
the Nerites, and the like. Were it not for this, the part which is
undefended by the shell would be very liable to injury by collision
with external objects
|
