^^2 O.V THE NUMBER OF POLAR BODIES AND [VI. 



histological character. For obviously, such a character pre- 

 supposes the existence of an idioplasm with a considerable 

 degree of histological specialization, which must be contained 

 in the nucleus of the egg-cell. We know, on the other hand, 

 that when its growth is complete, after the formation of yolk 

 and membranes, the ^gg contains germ-plasm, for it is capable 

 of developing into an embryo. We have therefore, as it 

 were, two natures in a single cell, which become manifest 

 one after the other, and which, according to our fundamental 

 conception, can only be explained by the presence of two 

 different idioplasms, which control the egg-cell one after the 

 other, and determine its processes of development. At first 

 a nucleoplasm leading to histological specialization directs 

 the development of the ^gg and stamps upon it a specific 

 histological character ; and then germ-plasm takes its place, 

 and compels the ^gg to undergo development into an embryo. 

 If then the histogenetic or ovogenetic nucleoplasm of the 

 egg-cell can be derived from the germ-plasm, but cannot be 

 re-transformed into it (for the specialized can be derived from 

 the generalized, but not the generalized from the specialized), 

 we are driven to the conclusion that the germ-plasm, which 

 is already present in the youngest egg-cell, first of all ori- 

 ginates a specific histogenetic or ovogenetic nucleoplasm which 

 controls the egg-cell up to the point at which it becomes 

 mature ; that its place is then taken by the rest of the un- 

 changed nucleoplasm (germ-plasm), which has in the meantime 

 increased by growth ; and that the former is removed from 

 the ^gg in the form of polar bodies— a removal which has 

 been rendered possible by the occurrence of nuclear division. 

 Hence the formation of polar bodies signified, in my opinion, 

 the removal of the ovogenetic part of the nucleus from the 

 mature egg-cell. Such removal was absolutely necessary, 

 if it is impossible that the ovogenetic nucleoplasm can be 

 re-transformed into germ-plasm. Hence the former substance 

 cannot be made use of after the maturation of the Qgg^ and 

 it must even be opposed to the commencement of embryonic 

 development, for it is impossible that the egg can be controlled 

 by two forces of different kinds in the same manner as it 

 would have been by one of them alone. I therefore concluded 

 that the influence of the ovogenetic idioplasm must be re- 



