The Dissection of the Fish 31 
one. In the bony fishes the stomach is an enlarged area, either 
siphon-shaped, with an opening at either end, or else forming 
a blind sac with the openings for entrance (cardiac) and exit 
(pyloric) close together at the anterior end. In the various 
kinds of mollets (Mugil) and in the hickory shad (Dorosoma), 
fishes which feed on minute vegetation mixed with mud, the 
stomach becomes enlarged to a muscular gizzard, like that of a 
fowl. Attached near the pylorus and pouring ‘their secretions 
into the duodenum or small intestine are the pyloric ceca. 
These are tubular sacs secreting a pale fluid and often almost as 
long as the stomach or as wide as the intestine. These may be 
very numerous as in the salmon, in which case they are likely to 
become coalescent at base, or they be few or altogether wanting. 
Besides these appendages which are wanting in the higher 
vertebrates, a pancreas is also found in the sharks and many 
other fishes. This is a glandular mass behind the stomach, its 
duct leading into the duodenum and often coalescent with the 
bile duct from the liver. The liver in the lancelet is a long 
diverticulum of the intestine. In the true fishes it becomes a 
large gland of irregular form, and usually but not always pro- 
vided with a gall-bladder as in the higher vertebrates. Its 
secretions usually pass through a ductus cholodechus to the 
duodenum. 
The spleen, a dark-red lymphatic gland, is found attached 
to the stomach in all fish-like vertebrates except the lancelet. 
The lining membrane of the abdominal cavity is known as the 
peritoneum, and the membrane sustaining the intestines from 
the dorsal side, as in the higher vertebrates, is called the mesen- 
tery. In many species the peritoneum is jet black, while in 
related forms it may be pale in color. It is more likely to be 
black in fishes.from deep water and in fishes which feed on 
plants. 
The Spiral Valve.-—In the sharks or skates the rectum or 
large intestine is peculiarly modified, being provided with a spiral 
valve, with sometimes as many as forty gyrations. A spiral 
valve is also present in the more ancient types of the true fishes 
as dipnoans, crossopterygians, and ganoids. This valve greatly 
increases the surface of the intestine, doing away with tie neces- 
sity for length. In the bowfin (Amza) and the garpike (Lepr- 
