234 THE CONTINUITY OP THE GEBM-PLA8M AS THE 



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 ex- 

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

 eggs with which we are acquainted, the nucleus moves to the sur- 

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

 its well-known transformation. It is obvious that it is there sub- 

 jected to different influences from those which would have acted 

 upon it in the centre 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 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 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 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 1 . 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 present in the segmentation nucleus of fertilization, as 

 compared with those present in the segmentation nucleus of par- 

 thenogenesis. 



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

 ment against my theory. In these insects, the same egg will de- 

 velope into a female or male individual, according as fertilization 



1 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. 



