SOMATOGENESIS 255 



genes freighted with the handicap of idiocy ever pro- 

 duce an intellectual leader. 



5. THE ROLE OF GENES IN SOMATIC DIFFERENTIATION 



An essential feature of cellular differentiation is the 

 unequal division of material, both quantitatively and 

 qualitatively. When we trace the complicated adult 

 organism backward step by step to the fertilized egg 

 from which it started we see that its complexity has 

 arisen largely through this process of unequal division. 



Moreover, each stage in the "process of becoming" is 

 conditioned upon what has already happened in pre- 

 ceding stages, since differentiation is a forward-moving 

 sequence of events. Just as the roof of a house must 

 follow and not precede the erection of walls which are 

 placed on a foundation previously prepared, so the he- 

 reditary matter in the gene must pass through a long 

 series of preliminary steps of differentiation before 

 finally coming to manifest fruition in the soma. 



Weismann, who by the process of logic rather than 

 experimentally located the germinal substance in the 

 nucleus of the germ-cell, assumed an elaborate theoreti- 

 cal system of "biophores," "ids," "idants," etc., where- 

 by a differential distribution of the nuclear substance 

 of the germ-cells to the various somatic cells is supposed 

 to occur. This is diagrammatically shown in Fig- 

 ure 79. 



Subsequent discovery and confirmation of the facts 

 of mitosis, however, have shown that the germplasm 

 does not influence the development in this way, for 



