CLOACAL GLANDS OF MALE NECTURUS 459 



turtles and crocodiles which develops from the ventral wall of 

 the cloaca. The cloaca of urodeles is doubtless homologous with 

 the cloaca of both reptiles and mammals, and from the ventral 

 portion of this the special organ of copulation has been evolved. 

 The cloacal glands of urodeles and the urethral glands of mono- 

 tremes and marsupials perform the same function, i.e., furnish 

 a fluid or semifluid vehicle for the spermatozoa, but this simi- 

 larity of function is not sufficient to establish the homology, since 

 we have many instances of similar structures performing the 

 same function in different groups of vertebrates, but they are 

 not homologous. However, even if the homology between the 

 cloacal glands of urodeles and the urethral glands of lower mam- 

 mals cannot be established, it is at least interesting to note that 

 in such widel}^ separated groups of vertebrates the same type of 

 gland has been evolved in a similar position to serve apparently 

 similar needs. 



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