Da the Life-Histoiy and Development of the Genus Myzostoma. 573 



hermaphrodite, and Iiere we bave the same tliing witliin the much nar- 

 rower limits of one geuus. 



It now becomes of importanee to endeavour to find out , which is 

 the more primitive conditiou, hermapbroditism or uuisexuality in these 

 particular cases. Most writers ^ on Zoology bave simply assumed, that 

 the hermapbroditism of such forms as Myzostoma and the Cirripedia is 

 the primitive coudition. The problem which of the two states is in par- 

 ticular cases the original has been but little attacked. 



We are, I think, entitled to assume that among the Cirripedia her- 

 maphroditism is secondary. For the lowest Crustaceans are all uni- 

 sexual , and it is only in such bighly modified forms as the Cirripedia 

 and RJiizocephala that we meet witb hermapbroditism. Indeed from a 

 survey of parasites generally one might almost say , that they bave a 

 tendency to become hermaphrodite, or that there is a tendency in para- 

 sitic life to produce bermaphroditism. 



If it be the case that bermaphroditism in Cirripedia is secondary 

 then the most primitive of the forms described by Darwin, at least so 

 far as sexuality goes, would be Ibla Cumingii^ which is uuisexual, and 

 possesses males capable of taking in food. The next stage would be 

 Scalpellum oriiatum^ witb successive pairs of short-lived males destitute 

 of mouth and stomach. The third Scalpellum vulgare^ hermaphrodite 

 witb from one to six short-lived males without mouth or stomach. Fin- 

 ally if the period between the appearance of two successive generations 

 of short-lived males becomes, to use a mathematical term, infinite, that 

 is if the males entirely disappear , then we get the ordinary herma- 

 phrodite Cirripedes without males such as Lepas. 



Darwin's case 3 has not been mentioned above. In this case of 

 hermaphrodites witb males which bave mouth and stomach, the pas- 

 sage is more direct from simple unisexual forms. 



And now turning to the Annelida , we find there just as we found 

 in the Crustacea that the lowest forms are mostly unisexual. Only in 

 bighly modified forms 2 such as the leeches, and Oligochaeta and the 

 parasitic genus Myzostoma do we find bermaphroditism. 



My own view is that primitively all the Segments of an Annelid 

 produce either ova or spermatozoa. Later some of the Segments may 

 lose all sexual function wbile in others, by a gradually acquired ten- 



1 Comp. Huxley, Anatomy of Invertebrated Animals. 1877. p. 67, and 

 Claus, Grundzüge der Zoologie. 



- Unfortunately two species of Folygordius are hermaphrodite , while one is 

 unisexual. 



