EPIGENESIS OR EVOLUTION. 119 



paralleled by the " circuitus theoreticus " : the course of 

 speculation seems to start from a new beginning to develop 

 along a special course, and to become a complete organon, 

 only to fall back again into the same germ from which it 

 arose. 



The theory of determinants, which is the modern expres- 

 sion of individual evolution, is not, however, universally 

 accepted. There is another theory, which may be called 

 epigenetic, founded on the assumption that the division of 

 the egg is not qualitative, but quantitative. According to 

 this view the daughter cells, at every cell division, no matter 

 what may be their prospective character, receive exactly 

 equal amounts as well as kinds of nuclear material, in which 

 the elementary particles are supposed to reside. The 

 differentiation of the resulting cells is determined in each 

 case by cellular interaction, the development of each cell is 

 determined by its relation to its fellows, or as it has been 

 neatly put, "its prospective character is a function of its 

 location ". The advocates of this theory point to experiment 

 and observation in support of it. For example, E. B. 

 Wilson has shown that in the egg of Amphioxus each of 

 the first two blastomeres, if separated mechanically from the 

 other, goes through a normal course of development, result- 

 ing not in a half embryo, but in a complete embryo which 

 is half the normal size. Similarly each of the first four 

 blastomeres, if separated from its fellows, gives rise to a 

 normal embryo of quarter size. But in the eight-cell stage 

 the course of development becomes obscured, and definite 

 results are not arrived at. Similar observations have been 

 made on the eggs of Echinus. These experiments are 

 held to prove that the division of the ovum must be 

 quantitative only, since the "daughter cells have the same 

 capacity to produce the organism as the mother cell, size 

 only excepted. In later stages, e.g., the eight-cell stage, 

 the idioplasm of each cell has become modified by the 

 interaction of the adjoining cells, and has, therefore, lost 

 to some degree the primitive power of giving rise to the 

 whole organism, and this modification with the corresponding 

 loss of formative power becomes accentuated with every 



