THE STRUGGLE FOR EXISTENCE IVA 



cliaiii^cs hroiii^lit about tlic <I\viiidlin<? of other parts fioiii 

 wliicli so miicli activity was no longer required. The 

 result was "that tlie wlioh^ organization of the animal 

 Ix'cainc more and more adapted to browsing on higli 

 foliage." Tliis same principle was applied to exj)laiii 

 many other structural peculiarities. To clearly under- 

 stand this problem, it is necessary to resort to the theory 

 of inheritance. 



In speaking of inheritance we said that the parent was 

 rather the trustee of the germ-plasm than the producer 

 of tlic child. In higher plants and animals the function 

 of reproduction is not performed by the body as a whole, 

 but is given over to special groups of cells, the germ 

 ceUs, constituting the ovaries and testes. It is from 

 these cells that new individuals arise. In view of this 

 the problem we have just been considering is not so 

 simple. For exami)le, how can the enlargement of a 

 muscle due to exercise, so affect the germ cells, which 

 lie at some distance from the muscle in question, as to 

 cause the new individual, which shall arise from these 

 germ cells, to have the corresponding muscle in its own 

 body enlarged? Under ordinary conditions it is only 

 the gervi cells in the body which have any descendants 

 in the following generation."^^ In the body there are 

 muscle cells, bone cells, nerve cells, etc. Weismann used 

 the term soma to include all the cells of the body which 

 are not germ cells. Now the whole body of the offspring 

 comes from the union of two germ cells; an egg from one 

 parent and a spermatozoon from the other.''' No somatic 

 cell gives rise to any i)art of the offspring. AVhile the 

 fertilized egg is developing into an adult organism it 

 divides into a numbei' of ])ortions called l)last.omeres, 



7-a ]\retcalf, op. fit.. ]i. 77. '■^' Ihid., p. 7.'^. 



