10 GENETICS 



a single parent or of two parents, while heredity is 

 simply "organic resemblance based on descent." 



4. SOMATOPLASM AND GERMPLASM 



In forms that reproduce sexually there theoretically 

 occurs a differentiation of the body substance into 

 what Weismann terms somatoplasm and germplasm. 



The somatoplasm includes the body tissues, that 

 is, the bulk of the individual, which is fated in the 

 course of events to complete a life-cycle and die. 

 The germplasm, on the contrary, is the immortal 

 fragment freighted with the power to duplicate the 

 whole organism and which, barring accident, is des- 

 tined to live on and give rise to new individuals. 



The germplasm thus carries potencies for develop- 

 ing both germplasm and somatoplasm, while the 

 somatoplasm, according to this conception, has only 

 the power to reproduce more of its own kind. More- 

 over, the germplasm is not formed afresh in each gen- 

 eration, neither does it arise anew when the individual 

 reaches sexual maturity, but it is a continuous sub- 

 stance present from the beginning. Although this 

 theory of the continuity of the germplasm has been 

 actually demonstrated in comparatively few instances, 

 all the facts we know concerning the behavior of the 

 germinal substance are consistent with it. 



In many of the Protozoa the entire organism is 

 possibly comparable to germplasm, but in all forms 

 of life that are compounded of several cells the germ- 

 plasm is probably set aside early in the development 



