THE ALIMENTARY CANAL. "9 
pions have no stomachal cavity—a straight intestine passes 
directly through the body. 
In bivalve Mollusks, like the Clam, the mouth (which 
is a mere aperture) opens at once into the stomach, which 
lies imbedded in a large liver, and the intestine, describ- 
ing a few turns, passes directly through the heart.* In 
the univalve Mollusks, like the Snail, the gullet is long, 
and frequently expands into a crop; the stomach is often 
double, the anterior being a gizzard provided with teeth 
for mastication ; the intestine passes through the liver, and 
ends in the fore part of the body, usually on the right side. 
The highest Mollusks, as the Cuttle-fish and Nautilus, 
exhibit a marked advance. A mouth with powerful 
mandibles leads to a long gullet, which ends in a strong 
muscular gizzard resembling that of a fowl.” Below 
this is a cavity, which is either a stomach or duodenum; 
it receives the bile from a large liver. The intestine 
is a tube of uniform size, which, after one or two slight 
curves, bends up, Fa 
and opens into the 
“funnel” near the 
mouth. 
Fishes have a 
simple, short. and 
wide alimentary 
canal. The stom- 
ach is separated 
from the intestine 
by a narrow “ py- 
loric” orifice, or 
valve, but is not 
so clearly distin- 
onic . Fig. 42.—Alimentary Canal of the Oyster: a, stomach 
guished from the laid open; d, liver; b,c, d, f, convolutions of the intes- 
gullet, so that tine; g, anal aperture; 7, 0, auricle and ventricle; 1, m, 
i ? ; adductor muscle; h, k, lobes of mouth divided to show 
regurgitation 1S _ the venous canals at the base of the gills. 
