37^ ON THE NUMBER OF POLAR BODIES AND [VI. 



germ-plasms would continually decrease in the course of genera- 

 tions,— a process which would necessarily end with their com- 

 plete reduction to a single kind, viz. to the paternal or the 

 maternal germ-plasm. But the occurrence of such a result is 

 disproved by the facts of heredity. Although such an early 

 occurrence of the ' reducing division ' would offer advantages 

 in that nothing would be lost, for both daughter-nuclei would 

 become eggs, instead of one of them being lost as a polar body, 

 nevertheless I do not believe that it really occurs : weighty 

 reasons can be alleged against it. 



Above all, the facts of parthenogenesis are against it. If the 

 number of ancestral germ-plasms received from the parents 

 were reduced to half in the ovary of the young animal, how 

 then could parthenogenetic development ever take place ? It 

 is true that we cannot at once assert the impossibility of an 

 early ' reducing division ' on this account, for as I have shown 

 above, the power to develope parthenogenetically depends 

 upon the quantity of germ-plasm contained in the mature egg ; 

 the necessary amount might be produced by growth, quite 

 independently of the number of different kinds of ancestral 

 germ-plasms which form its constituents. The size of a heap 

 of grains may depend upon the number of grains, and not upon 

 the number of different kinds of grains. But in another respect 

 such a supposition would lead to an unthinkable conclusion. 

 In the first place, the number of ancestral germ-plasms in the 

 germ-cells would be diminished by one half in each new genera- 

 tion arising by the parthenogenetic method ; thus after ten 

 generations only yqVj of the original number of ancestral germ- 

 plasms would be present. 



Now, it might be supposed that the ' reducing division ' of the 

 young egg-cells was lost at the time when the parthenogenetic 

 mode of reproduction was assumed by a species ; but this 

 suggestion cannot hold, because there are certain species in 

 which the same eggs can develope either sexually or partheno- 

 genetically (e.g. the bee). It seems to me that such cases 

 distinctly point to the fact that the reduction in the number of 

 ancestral germ-plasms must take place immediately before the 

 commencement of embryonic development, or, in other words, 

 at the time of maturation of the egg. It is only decided at this 

 time whether the ^^g of the bee is to develope into an embryo 



