98 EVOLUTION AND MAN S PLACE IN NATURE 



Weismann states thus : Either the substance of the 

 parent germ-cell is capable of undergoing a series of 

 changes, which, after the building up of a new indi 

 vidual, leads back again to identical germ-cells; or 

 the germ- cells are not derived at all, as far as their 

 essential and characteristic substance is concerned, 

 from the body of the individual, but they are derived 

 directly from the parent germ-cell. 1 The latter alterna 

 tive is the one he prefers. Weismann s hypothesis is 

 that in each ontogeny, a part of the specific germ- 

 plasm is not used up in the construction of the body 

 of the offspring, but is reserved unchanged for the 

 formation of the germ-cells of the following genera 

 tion. 2 According to this view, the nuclear substance 

 is the sole bearer of hereditary tendencies ; 3 these, 

 on the hypothesis, are not drawn from the parent 

 body. Acquired variations cannot be transmitted. A 

 start is obtained only by union of the nuclear sub 

 stance of the male and female parents, 4 the fusion 

 of two hereditary tendencies. 5 On this hypothesis, 

 the germ-plasm becomes the centre of vitality, having 

 true continuity of existence a kind of immortality, 

 he would say. Individual life has thus only its 

 limited term, advancing to maturity, thereafter yield 

 ing to decay, and departing without even handing on 

 acquired variations, profitable to the individual under 

 its conditions of life. Such, in outline, is Weismann s 

 hypothesis. He does not claim that it is more than 

 hypothesis, saying, it is possible that continuity of 

 the germ-plasm does not exist in the manner in which 

 I imagine that it takes place, for no one can at present 



1 Essay upon Heredity, vol. i. p. 170. 2 Ibid., p. 170, 



3 Ibid., p. 180. * Ibid., p. 181. 6 Ibid., vol. ii. p. 111. 



