CHAPTER X 



PARENTS AND OFFSPRING 



We have seen that the hereditary substance — the germ-plasm 

 — of every organism is composed of ids. We have also seen that 

 the hereditary substance is transmitted intact from one generation 

 to another, that it is continuous, not made afresh in the course 

 of generations. The doctrine of the contiuuity of the germ- 

 plasm must be accepted as one of the most important conclusions 

 of biological research since Darwin's statement of the law of 

 natural selection. Thus, the germ-plasm of every individual is 

 composed of the ids of all his ancestors. This does not mean 

 that the germ-plasm of a human being includes the ids of the 

 AmcBba ; for the ids do not remain eternally immutable. In 

 reality, no single id corresponds to the likeness of any one of our 

 animal ancestors ; for the character of those ancestors was deter- 

 mined, not by any single, but by all, or by the majority, of the 

 ids of the germ-plasm of each. And in the course of generations 

 many ids must have been eliminated as the result of the so-called 

 " reducing divisions " ; and in this elimination of ancestral ids, 

 according to Weismann, we find the reason for the expidsion 

 of the polar bodies from the egg, and for the successive divisions 

 of the sperm-ceU before it attains maturity. The share 

 of the Amoeba in the constitution of the germ-plasm of the 

 human being must necessarily be infinitesimal ; during the 

 course of ages amphimixis and successive reductions have been 

 perpetually " renewing " the germ-plasm of succeeding genera- 

 tions, so to speak, mingUng new ids, effecting new combinations, 



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