IV.] FOUNDATION OF A THEORY OF HEREDITY. 219 



quantity of nuclear substance must be reduced in order to 

 become equal to that of the generally minute sperm-nucleus, 

 and that the proportions for nuclear conjugation are in this 

 way adjusted. 



The first view seems to me to be disproved by the fact that 

 male as well as female qualities are transmitted by the egg-cell, 

 while the sperm-cell also transmits female qualities. The germ- 

 plasm of the nucleus of the ^^g cannot therefore be considered 

 as female, and that of the sperm-nucleus cannot be considered 

 as male : both are sexually indifferent. The last view has been 

 recently formulated by Strasburger, who holds that the quan- 

 tity of the idioplasm contained in the germ-nucleus must be 

 reduced by one half, and that a whole nucleus is again pro- 

 duced by conjugation with the sperm-nucleus. Although I 

 believe that the fundamental idea underljnng this hypothesis is 

 perfectly correct, viz. that the influence of each nucleus is as 

 largely dependent upon its quantity as upon its quality, I must 

 raise the objection that the decrease in quantity is not the ex- 

 planation of the expulsion of polar bodies. The quantity of 

 idioplasm contained in the germ-nucleus is, as a matter of fact, 

 not reduced by one-half but by three-fourths, for two divisions 

 take place one after the other. Thus by conjugation with the 

 sperm-nucleus, which we may assume to be of the same size 

 as the germ-nucleus, a nucleus is produced which can only 

 contain half as much idioplasm as was present in the ori- 

 ginal germ-nucleus, before division. Strasburger's view leaves 

 unexplained the question why the size of the germ-nucleus, 

 before the expulsion of polar bodies, was thus twice as large ; 

 and even if we neglect the theory of ovogenetic nucleoplasm 

 and assume that this larger nucleus was entirely made up of 

 germ-plasm, it must be asked why the ^%g did not commence 

 segmentation earlier. The theory which explains the sperm- 

 cell as the vitalizing principle which starts embryonic develop- 

 ment, like the spark which kindles the gunpowder, would 

 indeed answer this question in a very simple manner. But 

 Strasburger does not accept this theory, and holds, as I do, 

 a very different view, which will be explained later on. 



If, on the other hand, we assume that the germ-nucleus 

 contains two different kinds of nucleoplasm, the question is 

 answered quite satisfactorily. In treating of parthenogenesis, 



