Hermaphrodite 

 animals. 



Parasites or com- 

 mensals 



HERMAPHRODITISM IN MOLLUSCA. 39 



animals shows that hermaphroditism is characteristic almost 

 always of specialised forms (52). I will more particularly 

 mention fixation, parasitism, fluviatile or terrestrial life, as 

 specialisations accompanied by hermaphroditism, as the fol- 

 lowing few examples show : 



IPecten, Ostrea, Aspergillum, 

 Clavagella; various Serpulidse 

 (54), Cirripedes, Myzostomidse, 

 Ascidiae. 

 {Entoconcha, Entovalva, Ces- 

 todes, Trematodes, Hirudinea, cer- 

 tain Isopods, Myxine. 



, . I j- Valvata, Pulmonata, Oligochseta. 



In support of the opinion that hermaphroditism is a spe- 

 cialisation of the separation of the sexes, it may be remembered 

 that in a great number of unisexual glands individual variations 

 occur in which the elements of both sexes are produced, one of 

 the two kinds of element being an abnormal product. I will 

 cite merely a few instances : 



i. Batrachians : female frog (55). 

 ii. Fishes: female herring (56). 

 iii. Molluscs: Ampullaria, Anodonta. 

 iv. Chsetopods : ova in the testicle of Lurabricus (57). 

 V. Crustaceans: female Ap us (58), &c. 

 This phenomenon makes it possible to understand that the 

 hermaphrodite state can easily establish itself in certain 

 circumstances where it is useful for the same individual to 

 give rise to the products of both sexes (59). 



2. The establishment of hermaphroditism on the 

 female condition. — I cannot at present affirm that her- 

 raaphroditisim has everywhere grafted itself upon the female 

 organisation ; nevertheless the phenomenon ought to be 

 exhibited elsewhere than among the molluscs. 



As a matter of fact, there are several other groups in which 

 the male sex is preserved in the form of individuals, either 

 degraded or not, vrhen there are no longer any females, 



