40 PAUL PELSENEER. 



but only normal hermaphrodite individuals. This 

 is the case with — 



i. Various Myzostomidse. 



ii. Certain parasitic Isopods, e. g. the Cryptoniscidse. 



iii. Various Cirripedes, e.g. Scalpellum^ &c. 



And the study of one of these Cirripedes has led Delage to 

 the same conclusion as that which I have deduced from the 

 study of hermaphrodite molluscs : " Au debut, les Sacculines 

 etaient des animaux a sexes distincts, dont les femelles sont 

 devenues hermaphrodites beaucoup plus tard '^ (60). 



Lastly, the same seems to be true among osseous fishes in 

 Serranus, according to Giinther (61), viz. that the herma- 

 phrodite individuals are transformed females. This has been 

 confirmed by Brock, who has specially studied the genital 

 organs of fishes. He concludes that "die hermaphrodi- 

 tischen Knochenfische sind weibliche Individuen, 

 in deren Ovarium sich an Stelle einiger Ovarial- 

 lamelle ein Hoden sich entwickelt hat (62). And, 

 on the other hand, the vas deferens of Serranus is not homo- 

 logous with that of other osseous fishes (63) ; it is, accordingly, 

 like that of the Mollusca Anatinacea and Pulmonata (vide 

 supra, V, 2, ii), a new formation grafted on the female 

 condition. 



In these difierent cases the establishment of the hermaphro- 

 dite condition has been probably characterised by the follow- 

 ing successive stages : — Production of spermatozoa in a part of 

 the ovaries ; reduction of the size of the males and of their 

 number (hyperpolygyny) ; then complete replacement of the 

 female by the hermaphrodite form; and, lastly, the total dis- 

 appearance of the degraded males. 



Summing up. 

 A. The study of Mollusca, Myzostomidse, Crustacea, and 

 Pisces shows that in these groups the separation of the sexes 

 has preceded hermaphroditism ; various cases in other groups 

 tend to show that this is true universally ; and the same con- 

 clusion applies to plants. 



