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 coelom 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 coelom 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- 
terus 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. In Polypterus (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 
