12 GENETICS 



plasmal streams at the time of sexual reproduction, 

 as shown diagrammatically in Figure 2, in which 

 individuals are represented by triangles. From 

 this continuous stream of germplasm there split off 

 at successive intervals complexes of somatoplasm, or 

 "individuals," which go so far on the road of speciali- 

 zation into tissues that the power to be " born 

 again" is lost, and so after a time they die, while 

 the germplasm, held in reserve, lives on. 



This is what is meant by saying that a father and 

 son owe their mutual resemblance to the fact that they 

 are chips off the same block rather than by saying 

 that the son is a chip off the paternal block. Both 

 somatoplasm s are developments at different inter- 

 vals from the same continuous stream of germplasm 

 instead of one somatoplasm being derived from a 

 preceding one. As a matter of fact the germplasm 

 from which the son arises is modified by the addition 

 of a maternal contribution, so that father and son in 

 reality hold the same relation to each other that half- 

 brothers do. 



From the point of view of genetics, then, the real 

 mission of the somatoplasm, which is so marvelously 

 differentiated into all the various forms that we call 

 animals and plants, is simply to serve as a temporary 

 j domicile for the immortal germplasm. Thus the 

 parent becomes as it were the "trustee of the germ- 

 plasm, " but not the producer of the offspring. 



In the light of these preliminary explanations it is 

 plain that the hopeful point of attack in the science 

 of genetics must inevitably be the germplasm which 



