284 



SEXIL 



THISM 



the facts offer no difficulties. If special stimulations r. 

 duce modifications which tend to be inherited only ] 

 relation to those stimulations, it follows that the actions of 

 the male Copepod in seizing the female would produce 

 modifications of structure which would be confined in inherit- 

 ance to the adult period of life in the male, because that is 

 the only portion of the life-history of the species in which 

 those particular actions are exerted. 



Cirripedia. The sexual relations in these sessile and 

 much degenerate crustaceans are very remarkable. In many 

 of the typical forms, including all the Balanidse, which are 

 without peduncles, there is no sexual dimorphism, since all 

 the individuals are alike, and all hermaphrodite. We may 

 consider it most probable, since the sedentary habits of these 

 animals is evidently secondary, that they are descended 

 from forms which were bisexual like all other Crustacea. 

 The hermaphrodites are then probably modified females, 

 and we have to consider the question how females came to 

 develop testicular organs and produce spermatozoa. I must 

 admit that at present I have no suggestions to make concerning 

 the influence of the conditions of life in developing hermaphro- 

 ditism. I have been considering the influence of such conditions 

 on the structure of those parts of the body which are in direct 

 relation to external conditions, and know nothing of their 

 influence on the primary generative organs. It is, however, 

 interesting to note that there are some Cirripides which are 

 simply bisexual and sexually dimorphic, and which may be 

 taken to retain the original condition with respect to the 

 separation of the sexes. Curiously enough hermaphrodite 

 forms and bisexual forms occur within the same genus, 

 namely, Scalpellum, one of the stalked Cirripedes, and IMa 

 of the same family. Thus Scalpellum ornatum of the coasts 

 of South Africa has separate sexes, while Scalpellum vulgare of 

 the North Sea and European coasts is hermaphrodite. Where 



