356 CLASSICS OF MODERN SCIENCE 

 segmentation nucleus. In addition to these considerations we must 

 not leave the substance of the cell-body altogether out of account, 

 for, although it is not the bearer of the tendencies of heredity, it 

 must be necessary for every change undergone by the nucleus, and it 

 surely also possesses the power of influencing changes to a large 

 extent. There must be some reason for the fact that in all animal 

 eggs with which we are acquainted, the nucleus moves to the surface 

 of the egg at the time of maturation, and there passes through its 

 well known transformation. It is obvious that it is there subjected 

 to different influences from those which would have acted upon it 

 in the center of the cell-body, and it is clear that such an unequal 

 cell-division as takes place in the separation of the polar bodies could 

 not occur if the nucleus remained in the center of the egg. 



This explanation of the necessity for fertilization does not exclude 

 the possibility that, under certain circumstances, the substance of the 

 egg-nucleus may be larger, so that it is capable of forming four loops. 

 Eggs which thus possess sufficient nucleoplasm, viz., germ-plasm, for 

 the formation of the requisite four loops of normal size (namely, of 

 the si2e which would have been produced by fertilization), can and 

 must develop by the parthenogenetic method. 



Of course the assumption that four loops must be formed has only 

 been made for the sake of illustration. We do not yet know whether 

 there are always exactly four loops in the segmentation nucleus. I 

 may add that, although the details by which these considerations are 

 illustrated are based on arbitrary assumptions, the fundamental view 

 that the development of the egg depends, ceteris paribus, upon the 

 quantity of nuclear substance, is certainly right, and follows as a 

 necessary conclusion from the ascertained facts. It is not unlikely 

 that such a view may receive direct proof in the results of future 

 investigations. Such proof might, for instance, be forthcoming if 

 we were to ascertain, in the same species, the number of loops pres- 

 ent in the segmentation nucleus of fertilization, as compared with those 

 present in the segmentation nucleus of parthenogenesis. 



The reproductive process in bees will perhaps be used as an argu- 

 ment against my theory. In these insects the same egg will develop 

 into a female or male individual, according as fertilization has or has 

 not taken place, respectively. Hence one and the same egg is capable 



