THE PERCH 205 



Exercise 5. Draw a semidiagrammatic sketch of the digestive tract 

 and label carefully all its parts. 



The Urinogenital 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 6. 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- 

 neys. These organs are a pair of slender, deep-red bands which 

 lie close against the dorsal body wall, one on each side of the 

 vertebral column. Their anterior ends unite just dorsal to the 

 oesophagus and form a large, dark-colored median mass called 

 the head kidney, which extends across the body cavity. Dissect 

 away the remains of the oesophagus and note the exact shape 

 and extent of the head kidney. The ureters are a pair of tubes 

 which run along the entire length of the medial borders of the 

 kidneys, joining at their hinder ends. The single vessel thus 

 formed then passes to the minute urinary pore just back of the 

 genital pore ; a small urinary bladder projects from the median 

 portion of the ureters. 



