40 VERTEBRATE ZOOLOGY 



The intestine begins at the pylorus and extends to the anus. It 

 is composed of three divisions,— the duodenum (which includes the 

 anterior loop of the intestine, between the limbs of which the 

 spleen lies), the small intestine, and the rectum,— the boundary 

 between the last two divisions being the circular ridge about an 

 inch in front of the anus. The liver is a large gland which com- 

 municates with the intestine by means of the bile duct. This duct 

 emerges from the gall bladder, which lies against the posterior 

 surface of the liver, receives a number of branch ducts from the 

 liver, and joins the intestine near the base of the pyloric append- 

 ages. A pancreas has not been found in the perch. 



Exercise 6. Draw a semidiagrammatic sketch of the digestive tract 

 and label carefully all its parts. 

 Slit open the stomach and a portion of the intestine and examine 

 their inner surface. 



The Urogenital System; the Male Genital Organs. The testes 

 are a pair of white, elongated bodies which lie in the abdominal 

 cavity just ventral to the air bladder, to which they are joined 

 by a mesentery. They taper toward the hinder end and finally 

 fuse together, the median portion thus formed passing directly 

 to the genital pore just behind the anus. The actual size of the 

 testes depends upon the sexual condition of the animal ; during 

 the breeding season they are large and may extend into the anterior 

 portion of the abdominal cavity. 



The Female Genital Organs. The ovary is a median body which 

 lies in the abdominal cavity between the intestine and the air 

 bladder and is joined to the latter by a mesentery. It is an 

 elongated sac filled with small ova and varies in size with the 

 sexual condition of the animal ; no oviduct is present, the hinder 

 part of the ovary becoming gradually smaller and finally com- 

 municating with the outside through the genital pore just back 

 of the anus. 



Exercise 7. Make a sketch of the genital organs. 



The Urinary Organs. Remove the testes or the ovary. Dissect 

 the air bladder away from the body wall and remove it. Note 

 the thinness of its dorsal wall, where it lies just beneath the kid- 



