266 PARTHENOGENESIS VII 



these eoo^s fuse into one mass, around which a shell is 

 secreted, and which thus forms the actual egg — really 

 a threefold egg ; and from such a wonderfully formed 

 egg only one embryo develops. Unfortunately we 

 are not told what becomes of the germinal vesicles ; 

 according to the drawings they seem to disappear at 

 this stage. Siebold appears to have convinced him- 

 self that the fusion is a normal thing, and not due 

 to any pressure or osmotic action taking place during 

 the microscopical examination. The structure of the 

 ovary of Apus is figured in a plate. 



As to the other crustaceans named, which are 

 Artemia salina and Limnadia Hermanni, the occur- 

 rence of parthenogenetic broods is inferred from the 

 descriptions of other writers whose works are criti- 

 cised at some length, and also from examination of 

 specimens. It seems not impossible from an observa- 

 tion of Zenker that in Artemia salina parthenogenetic 

 alternate with digenetic broods. In the beginning of 

 the year 1851 this observer found three males among 

 one hundred females, later in July the same pond 

 furnished thousands of females, but not one male. 



In conclusion, Professor Siebold, whilst adopting 

 Leuckart's term " Arrenotoky," to designate the 

 phenomenon of the parthenogenetic production of 

 male offspring, as seen in the Hymenoptera, proposes 

 the parallel term, " Thelytoky," for the parthenogenetic 

 production of female offspring as demonstrated now 

 conclusively in some Lepidoptera and Crustacea. 

 It seems to us that a third term should also be avail- 

 able for the case of mixed offspring (that is, of two 



