CRAYFISH. 289 
end of the body, so that the antennules and antennz lie far 
in front of it. The fore-gut, which is lined by a chitinous 
cuticle, includes a short “gullet,” on the walls of which there 
are small glands, hypothetically called ‘‘salivary,” and a 
capacious gizzard, which is distinctly divided into two 
regions. 
In the anterior (cardiac) region there is 4 complex mill; in the 
posterior (pyloric) region there is a sieve of numerous hairs. The mill 
Fic. 144.—Longitudinal section of lobster, showing some 
of the organs. 
#., Heart; AO., ophthalmic artery; a@a., antennary artery; ah. 
hepatic artery ; S7Z., sternal artery; SA., superior abdominal 
artery; J7G., mid-gut ; DG., digestive gland; AG., hind-gut ; 
£x., extensor muscles of the tail; #2, flexor muscles of the tail: 
IA., inferior abdominal artery; G., gizzard ; C., cerebral ganglia 
P., pericardium ; 7., testes. 
is very complex ; there are supporting ‘‘ossicles” on the walls with 
external muscles attached 1o them, and internally projecting teeth which 
clash together and grind the food. Three of the teeth are conspicuous ; 
. a median dorsal tooth is brought into contact with two large laterals. 
On each side of the anterior part of the gizzard there are two limy 
discs or gastroliths, which are broken up before moulting, and though 
quite inadequate to supply sufficient carbonate of lime for the new 
skeleton, seem to have some relation to this process. The occurrence 
of chitinous cuticle, setee, teeth, and gastroliths in the gizzard, is 
intelligible when the origin of the fore-gut is remembered, and so is the 
dismantled state of this region when moulting occurs. 
The mid-gut is very short, but outgrowths from it form 
19 
