Chap. XIII.] 



SPERMATOZOA. 



477 



Where the method of reproduction becomes 

 sexual, we find sets of cells or glands which have a 

 different history and function ; these are the male 

 and female elements, and they may be found sepa- 

 rately in different individuals of the same species, or 

 they may both be formed in one individual ; in the 



D 



Fig. 201. Figure of Spermatozoon of, A, Guinea-pig (not quite mature) ; 

 B, the same seen sideways; c, Horse ; D, Newt. (After Klein.) 



latter case we have to do with hermaphrodite forms, 

 and these may be only structurally hermaphrodite, as 

 are the earthworm and the snail ; or they may also be 

 physiologically hermaphrodite, as the tapeworm, the 

 fluke, or the Ascaris nigrovenosa ; that is to say, the 

 male elements of one individual sometimes impregnate 

 the female cells of another individual, and in other 

 cases the two kinds of sexual cells of one and the same 

 individual come into union. It ordinarily happens 



