348 CLASSICS OF MODERN SCIENCE 

 to the obvious conclusion that parthenogenesis is based upon the non- 

 expulsion of polar bodies. Balfour distinctly states "that the func- 

 tion of forming polar cells has been acquired by the ovum for the 

 express purpose of preventing parthenogenesis." 



It is obvious that I cannot share this opinion, for I regard the 

 expulsion of polar bodies as merely the removal of the ovogenetic 

 nucleoplasm, on which depended the development of the specific histo- 

 logical structure of the egg-cell. I must assume that the phenomena 

 of maturation in the parthenogenetic egg and in the sexual egg are 

 precisely identical, and that in both, the ovogenetic nucleoplasm must 

 in some way be removed before embryonic development can begin. 



Unfortunately the actual proof of this assumption is not so com- 

 plete as might be desired. In the first place, we are as yet uncertain 

 whether polar bodies are or are not expelled by parthenogenetic eggs ; 

 for in no single instance has such expulsion been established beyond 

 doubt. It is true that this deficiency does not afford any support to 

 the explanation of Minot and Balfour, for in all cases in which polar 

 bodies have not been found in parthenogenetic eggs, these structures 

 are also absent from the eggs which require fertilization in the same 

 species. But although the expulsion of polar bodies in partheno- 

 genesis has not yet been proved to occur, we must assume it to be 

 nearly certain that the phenomena of maturation, whether connected 

 or unconnected with the expulsion of polar bodies, are the same in 

 the eggs which develop parthenogenetically and in those which are 

 capable of fertilization, in one and the same species. This conclu- 

 sion depends, above all, upon the phenomena of reproduction in bees, 

 in which, as a matter of fact, the same egg may be fertilized or may 

 develop parthenogenetically, as I shall have occasion to describe in 

 greater detail at a later period. 



Hence when we see that the eggs of many animals are capable of 

 developing without fertilization, while in other animals such develop- 

 ment is impossible, the difference between the two kinds of eggs must 

 rest upon something more than the mode of transformation of the 

 nucleus of the germ-cell into the first segmentation nucleus. There 

 are, indeed, facts which distinctly point to the conclusion that the 

 difference is based upon quantitative and not qualitative relations. 

 A large number of insects are exceptionally reproduced by the par- 

 thenogenetic method, e. g., in Lepidoptera. Such development does 



