IV.] FOUNDATION OF A THEORY OF HEREDITY. 243 



fertilization, the nucleus being subject to the same conditions of 

 nutrition in both cases. Strasburger ^ considers that partheno- 

 genesis may be interpreted by one of three possible explana- 

 tions. First, he suggests that especially favourable nutrition 

 may lead to the completion of the nuclear idioplasm. But if 

 this assumption be made, we must ask why a part of the 

 idioplasm should be previously expelled, when immediately 

 afterwards the presence of an equal amount becomes necessary. 

 Such a view can only be explained by the above-made assump- 

 tion that the expelled nucleoplasm has a different constitution 

 from that possessed by the nucleoplasm which is afterwards 

 formed. It is true that we do not yet certainly know whether 

 a polar body is expelled in eggs in which parthenogenesis 

 occurs, but we do know that the ^^^g of the bee passes through 

 the same stages of maturation whether it is to be fertilized or 

 not. I can hardly accept Strasburger's second suggestion, 

 'that under some favourable conditions of nutrition half [or 

 perhaps better, a quarter] of the idioplasm of the egg-nucleus 

 is sufficient to start the processes of development in the cyto- 

 idioplasm.' Finally, his third suggestion, ' that the cyto-idioplasm, 

 nourished by its surroundings and thus increased in quantity, 

 compels the nucleus of the ^%^ to enter upon division,' presup- 

 poses that the cell-body gives the impulse for nuclear division, 

 a supposition which up to the present time remains at least 

 unproved. The ascertained facts appear to me to indicate 

 rather that the cell-body serves only as a medium for the 

 nutrition of the nucleus, and Fol's recently mentioned ob- 

 servations, which have been especially quoted by Strasburger 

 in support of his theories, seem to me to rather confirm my 

 conclusions. If supernumerary sperm-nuclei penetrate into 

 the ^gg^ they may, under the nutritive influence of the cell- 

 body, become centres of attraction, and may take the first step 

 towards nuclear and cell-division by forming amphiasters. 

 Such nuclei cannot control the whole cell-body and force it 

 to divide, but each one of them, having grown to a certain size 

 at the expense of the cell-body, makes its influence felt over 

 a certain area. Strasburger is quite right in considering this 

 process as a ' partial parthenogenesis.' Such partial partheno- 

 genesis presumably occurs in all egg-nuclei, but the latter 



^ 1. c, p. 150. 

 R 2 



