DETERMINING OF CELLULAR TYPES 35 



ids, difiers with tlie species. The human species is said to have 

 sixteen chromosomes in each nucleus, while certain crustaceans 

 have as many as 168. Each id contains in itself cM the pro- 

 perties of the organism, but the nature of the organism is always 

 decided by the complete complement of ids — that is, by the 

 organisation of the chromosomes. As a result of the mingling 

 of the parental elements in amphimixis the ids are of a hetero- 

 geneous nature, and we see that a vast number of combinations 

 are rendered possible by amphimixis. 



Through the mechanism of cell division during the embryonic 

 development — a mechanism ultimately referable to the vital 

 affinities of the biophors — ^homologous portions of each id (homo- 

 logous, yet composed of difierent types of determinants) pene- 

 trate into every cell. The general nature of every cellular type 

 that arises in the course of the development is thus determined by 

 an id complex, or rather by a complex of individually difEerent 

 determinants, which resolve themselves into their biophors. 

 The precise histological character of the cell is, however, deter- 

 mined by one single type of determinant ; the other determinants 

 contained in the cell remain inactive. The resolution of the 

 determinants into their component biophors, and their penetra- 

 tion into the cells, is determined by the internal conditions of 

 the determinants — that is to say, by their vital affinities, which 

 depend also in a large measure on the conditions of intracellular 

 nutrition. But there is another factor which also plays a part 

 in the " liberation " of the determinants— namely, the specific 

 attraction between a particular determinant and a particular 

 cell. Cases in which two sorts of homologous determinants are 

 present in a single cell — as we must conclude from such pheno- 

 mena as regeneration and polymorphism — compel us to accept 

 this hypothesis. 



In 1881 Wilhelm Roux expounded the fruitful conception of 

 a struggle of parts within the organism, or what we may call 

 histonal selection, the fundamental idea of which is that each 



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