238 THE CONTINUITY OF THE GERM-PLASM AS THE 



considers that parthenogenesis may be interpreted by one of three 

 possible explanations. 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 after- 

 wards the presence of an equal amount becomes necessary. Such a 

 view can only be explained by the above-made assumption 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 egg 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-idio- 

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

 nourished by its surroundings and thus increased in quantity, com- 

 pels the nucleus of the egg to enter upon division,' presupposes 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 observations, 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 egg, 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 amphiastors. 

 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 parthenogenesis presumably occurs 

 in all egg-nuclei, but the latter cannot attain to complete partheno- 

 genesis when, as in Fol's supernumerary sperm-nuclei, their powers 

 of assimilation are insufficient to enable them to reach the requisite 

 size. As before stated, the cell-body does not force the nucleus to 

 divide, but vice versa. It would, moreover, be quite erroneous to 



