14 Outline of Genetics 



such characters: (i) there is no known mechanism by 

 which somatic characters may be transferred to the germ 

 plasm; (2) the evidence that such a transfer does occur 

 is inconclusive and unsatisfactory; and (3) the theory 

 of the continuity of the germ plasm is sufficient to account 

 for the facts of heredity. 



When Weismann says that there is no known mech- 

 anism by which somatic characters can be transferred to 

 the germ plasm, to him it is equivalent to saying that it 

 is hard to see how the water that has gone over the dam 

 can return and affect the flow of the water upstream. 

 He assumes, of course, that the genu plasm is isolated 

 from the somatoplasm very early in the development 

 of the fertilized egg into an individual, and that w^hen it 

 is isolated it takes no active part in the history of the 

 body (see fig. i). The somatoplasm is thus merely 

 a carrier of the germ plasm, and is unable to affect 

 the character of it any more than a rubber hot- 

 water bag, although capable of assuming a variety of 

 shapes, can affect the character of the water it contains 

 (Walter 18). 



This early differentiation of germ plasm and body 

 plasm has been demonstrated rather strikingly in several 

 animals. In Ascaris megacephala, the following cy to- 

 logical situation was demonstrated by Boveri, in 1903 

 (DoNCASTER 7). Following the first division of the 

 zygote, the two daughter-cells come to differ from each 

 other through the apparent degeneration of some of the 

 cell constituents in one. That daughter which main- 

 tains the full cell equipment of the zygote thereby per- 

 petuates the capacities of the germ plasm, while the other 

 daughter, which has lost certain visible cell constituents, 



