Xo. 524] 



CHROMOSOMES AND HEREDITY 



segregation, otherwise, of materials. On the contrary, 

 the presumption is in favor of the view that the effects 

 are produced not by segregation, but by the relation of 

 the cells to each other, or to the whole. If this compar- 

 ison be admitted, it follows that at some stage in the 

 history of the germ cells of the hybrid similar effects 

 may take place in regard to each kind of the inherited 

 qualities (not characters). In this connection it should 

 be recalled that the germ cells of the hybrid have had a 

 long history before maturing. If the chromosomes are 

 the essential elements in producing or maintaining the 

 material constitution of the cells there has been an abun- 

 dant opportunity for the chromosomes to have produced 

 general effects of this kind. The way in which the cells 

 react will depend on the changes that the chromosomes 

 have produced in them. In other words, at some period 

 in their history when the germ cells have become, as it 

 were, hybrid throughout they develop one or another of 

 each of the alternate possibilities to a greater or to a less 

 degree. Since the same sort of process occurs in groups 

 of somatic cells where it results from the responsive ac- 

 tion of the parts on each other, so let us suppose in the 

 germ cells of the hybrid a similar relation determines the 

 fate of its different potentialities. 



Our general conclusion is, therefore, that the essential 

 process in the formation of the two kinds of gametes of 

 hybrids in respect to each pair of contrasted characters, 

 is a reaction or response in the cells, and is not due to a 

 material segregation of the two kinds of materials con- 

 tributed by the germ cells of the two parents. The reac- 

 tion differs in the germ cells of the hybrid from that of 

 either of the parental types because the material basis 

 of the germ cells differs owing to its dual origin. The 

 results are due. however, to difference in reaction, and 

 not to a separation of mixed materials. The general 

 point of view that underlies this conclusion is epigenetic, 

 while the contrasting view, that of separation of mate- 

 rials, is essentially one of preformation. 



