CHAPTER V 



THE UROGENITAL SYSTEM 



1. The Urogenital System. 



The excretory system of vertebrates consists of certain 

 excretory organs with their ducts. The reproductive sys- 

 tem consists of a pair of gonads or sexual glands and their 

 ducts. The reproductive glands use the ducts of the ex- 

 cretory system to transport their product of germ cells 

 to the exterior, hence these two systems are generally quite 

 closely united and are considered together as the urogenital 

 (urinogenital) system. Work out the urogenital system of 

 your specimen, then study the dissection of a specimen of 

 the other sex which is being prepared by another student. 



Males may be distinguished from the females by several 

 characters. Claspers are present on the male. The greater 

 part of the sides lacks scales in the male. There are also 

 fewer rows of spines along the middle of the back and tail. 

 The scales on the margin of the head are much enlarged. 

 Two rows of erectile spines are present on the lateral ex- 

 pansion of the trunk (about one inch from the margin). 

 These can be erected and lowered into depressions in the 

 skin. In the females, scales are present over the sides of 

 the body, several rows are present on the dorsal surface of 

 the tail and the dorsal median part of the body. The female 

 has no erectile spines. 



During the development of vertebrates there are three 

 more or less distinct excretory organs or kidneys. (1) The 

 pronephros is present in the embryonic stages of fishes and 



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