248 PARTHENOGENESIS VII 



this for one and the same reason. Perhaps the appar- 

 ently anomalous facts that an animal — or plant, as the 

 case may be — develops elaborate motile zoosperms and 

 copulatory organs, merely to fertilise its own egg ; and 

 that other animals and plants develop peculiarly con- 

 structed large cells, of a kind apparently especially 

 elaborated in the j)rogress of the general evolution of 

 life to provide for fertilisation, yet which never are 

 fertilised — are only to be explained as cases of persist- 

 ent structures with modified function. In the former 

 case, Agamogenesis, being sufficient to or necessitated 

 by the conditions of life, yet avails itself of the ap- 

 paratus inherited from gamogenetic ancestors ; whilst 

 similarly, in the second case (pseudova), Agamogenesis, 

 having advantages for the 23articular case (and not 

 being a common phenomenon in the group), instead of 

 making its appearance through new organs, avails itself 

 of the ovary inherited from gamogenetic progenitors. 

 Thus the unsignificant form of an ovum (unsignificant, 

 that is, so far as Agamogenesis is concerned) takes 

 the place of the more obviously appropriate bud or 

 fission-product. The phenomenon of iVlternation of 

 Generations, usually treated of in connection with 

 parthenogenesis, should by experiment on the physical 

 conditions accompanying its variations enable us to 

 ascertain a great deal more than is at present known 

 of what is the simification of the differentiation of 

 male and female sexual elements ; and it is from further 

 study of this and of true Parthenogenesis that progress 

 in this part of physiology may be expected. 



To return to Siebold's researches. The greater 



