THE EVOLUTION OF SEX 33 



body and becoming eventually separated into 

 a chain of buds. In other words, a means 

 has been evolved whereby an animal with a 

 complex body may continue to produce buds, 

 just as simple polyps do. (c) The third sug- 

 gestion is that the distinction between germ- 

 cells and body cells would justify itself in 

 leaving a free course for the differentiation 

 of body cells (as nervous, contractile, glandu- 

 Iar 3 and so on), and in securing that the repro- 

 ductive cells were in some measure at least 

 sheltered from the influences of the accidents 

 and incidents of bodily life. Reproduction 

 by special germ-cells obviates or lessens the 

 risk, attendant on asexual reproduction, that 

 the offspring share in the acquired bodily 

 defects of the parent. Of course it must 

 likewise operate against the transmission of 

 extrinsically acquired bodily gains. On the 

 other hand, the important constitutional gains 

 which begin as germinal variations are more 

 or less securely entailed by the germ-cell 

 method, in virtue of what is called the con- 

 tinuity of the germ-plasm (see our Evolution, 

 p. 114). Variations are indeed common 

 among asexually produced plants, as we see 

 at a Chrysanthemum show, but the germ-cell 

 method is even more productive. Some recent 

 work suggests that the nutritive and other 

 environment of the young germ-cells within 

 the body may serve to provoke germinal 

 variations, acting in fact as " liberating 

 stimuli." Thus the risk of transmitting bodily 

 defects is lessened, while the supply of heritable 

 changes of endogenous origin is increased. 

 Another advantage probably lies in the fact 

 c 



