IV.] FOUNDATION OF A THEORY OF HEREDITY. 239 



it must be necessary for every chancre 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 witli which we are acquainted, 

 the nucleus moves to the surface of the ^gg at the time of 

 maturation, and there passes through its well-known trans- 

 formation. It is obvious that it is there subjected to different 

 influences from those which would have acted upon it in the 

 centre of the cell-body, and it is clear that sucli an unequal 

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

 bodies could not occur if the nucleus remained in the centre 

 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 maybe 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 size which would have 

 been produced by fertilization), can and must develope 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 

 &gg depends, ceteris paribus, upon the quantity of nuclear sub- 

 stance, 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 present 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 

 argument against my theory. In these insects, the same egg 

 will develope into a female or male individual, according as 



^ We now know that the number of loops varies considerably in 

 different species, even when they belong to the same group of animals 

 (e.g. Nematodes).— A. W., 1888. 



