322 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



the posterior end of the mesonephros alone is involved. This is fre- 

 quently accompanied by a degeneration of the glomeruli of the tubules 

 concerned, so that this part of the mesonephros loses its excretory 

 character and becomes subsidiary to reproduction. With this forma- 

 tion of vasa efferentia the sperm never enters the ccelom except as this 

 is represented in the cavities of the mesonephric tubules. 



As a farther result the anterior end of the Wolffian duct becomes 

 purely reproductive in the male and is usually greatly coiled, this 

 portion being called the epididymis. In the amniotes, where the 

 hinder portion of the mesonephros is supplanted by the true kidney 

 (metanephros) , the whole Wolffian duct is a sperm duct (vas deferens) 

 in the male, while in the female it largely or completely degenerates. 

 In the amphibia and elasmobranchs the hinder end of the duct is both 

 reproductive and excretory in the male; in the female it is purely 

 excretory. 



In the ichthyopsida, other than elasmobranchs and amphibia, the 

 sperm is carried to the exterior in other ways, and there is no connexion 

 of the testes with the excretory organs. In the cyclostomes the sperm 

 escapes from the testes into the ccelom and then is passed to the exterior 

 by way of the abdominal pores (p. 124) which in the lampreys open 

 into a cavity (sinus urogenitalis) which also receives the hinder ends 

 of the Wolffian ducts. In the myxinoids the pores are united and 

 open to the exterior behind the anus and between it and the urinary 

 openings. 



The conditions found in the sturgeons (fig. 325, A) and in Polyp- 

 terns give a possible explanation to the aberrant structures of the tele- 

 osts. In the first group can be made out the vasa efferentia and the 

 two longitudinal canals connecting them, these extending the whole 

 length of the testis. InPolypterus (fig. 325, C) the connexion between 

 the testis and mesonephros is confined to the hinder portion of 

 organs, the anterior vasa efferentia and the longitudinal canal 

 disappearing in front, the longitudinal testicular canal taking the 

 sperm from the anterior end of the testis and carrying it farther back 

 for passage through the mesonephros. Here the anterior end of the 

 Wolffian duct is purely excretory. A farther concentration of the 

 efferent functions to the last vas efferens would give, with a few other 

 modifications, the conditions of the teleosts (fig. 325, B). In all of 

 this group there is no connexion of testes with mesonephroi. The 

 seminiferous tubules are connected by a longitudinal canal (apparently 



