ON MOLLUSCA. 199 
though more rarely, a sort of distinct crop, as in some brachio- 
cephala. Its direction, sometimes almost medial, as at its 
origin, is often from right to left, so as to unite itself to the 
stomach on this last side. 
The stomachal swelling, often simple and indistinct, is on 
the contrary, in a great number of species, divided into se- 
veral pouches or lodges. Sometimes even one of these pouches 
has its parietes comprised between two muscles very thick, 
almost as is the case in the gizzard of birds. In peronia and 
limneea the conformation is similar. We find also in many 
species, and among others in the monopleurobranches, that 
the internal membrane of the stomach is armed with corneo- 
calcareous productions, very analogous in their structure and 
composition to teeth, which occurs even in the shell. 
The stomach of the acephalous mollusca has not its parietes 
distinct. Of a form usually irregular, it appears hollowed in 
the tissue itself of the liver, which envelopes it on all sides, 
and pours in the bile through numerous apertures or sinuses, 
very large, in which very singular bodies are observable, 
whose use and mode of formation are completely unknown. 
They are named crystalline stylets, because they are usually 
in the form of stylets, the point of which is in the canals, and 
they are a little transparent. 
In the cephalous mollusca, where nothing similar has been 
yet remarked, the liver never completely envelopes the sto- 
mach, neither does it adhere to it. It is even most frequently 
carried back into the remotest part of the visceral mass, and 
to the very point of the spire. It is composed of lobes and 
lobules, the last of which are in the form of hollow globules. 
From each of these lobules springs one of the minute biliary 
ducts, which successively uniting, constitute one or three or 
four thick canals, opening freely into the stomach itself, or 
sometimes into the commencement of the intestine. This 
structure of the liver often permits it to be inflated with the 
