38 THE BREEDING OF ANIMALS 



these questions. That this process is one of fundamental 

 significance and is intimately connected with the problem 

 of how characters are transmitted, is certain. Mani- 

 festly its purpose is to provide for a constant number of 

 chromosomes in the body tissues. It is not, as some have 

 maintained, a mere mass reduction of the chromatin. 

 Weismann's ingenious theory of the germ-plasm attempts 

 to explain the process and to point out the hereditary 

 significance of reduction. In an earlier investigation, 

 Roux held that the hereditary qualities are represented 

 by the individual chromatin granules. During cell di- 

 vision, these arranged themselves side by side in the 

 spireme thread, and the splitting of the spireme thread 

 longitudinally actually resulted in halving each indi- 

 vidual chromatin granule. Quoting Wilson, 1 " Roux 

 assumes, as a fundamental postulate, that division of the 

 granules may be either quantitative or qualitative. In 

 the first mode, the group of qualities represented in the 

 mother granule is first doubled and then split into equiva- 

 lent daughter groups, the daughter cells, therefore, receiv- 

 ing the same qualities and remaining of the same nature. 

 In ' qualitative division,' on the other hand, the mother 

 group of qualities is split into dissimilar groups, which, 

 passing into the respective daughter nuclei, lead to a 

 corresponding differentiation in the daughter cells. By 

 qualitative divisions, occurring in a fixed and predeter- 

 mined order, the idioplasm is thus split up during ontogeny 

 into its constituent qualities which are, as it were, sifted 

 apart and distributed to the various nuclei of the embryo. 

 Every cell nucleus, therefore, receives a specific form of 

 chromatin which determines the nature of the cell at a 

 given period in its later history. Every cell is thus 



1 Loc. cit. 



