34 



SOCIAL EVOLUTION 



some of these form the germ cells of tlie new individual, 

 the remainder become its soma. The germ cells of one 

 generation are thus derived ahnost directly from the 

 genu, cells of the preceding generation.'^ One can now 

 understand more clearly the significance of the theory 

 of the continuity of germinal jDlasm. Professor Metcalf 



GLNERATION A 



GENERATION B 



GENERATION C 



GENERATION D 



GERM CELLS 



GERM CELLS 



GERM CELLS 



GERM CELLS 



SOMA 



SOMA 



SOMA 



SOMA 



From Metcalf, " Organic Evolution. " 



FiGUBE 7. Diagram of Inheritance of Body Cells and Germ Cells. 



has illustrated this principle by the simple diagram 

 shown in figure 7.^ 



The diagram shows "that both the germ cells and the 

 soma of any generation are derived from the germ 

 cells alone of the preceding generation." No modifica- 

 tion in a somatic cell of the parent could, therefore, 

 cause a corresponding modification in the soma of the 

 child; because the soma of the child is descended from 

 the parental ger7n cells. In the case of the athlete the en- 

 larged muscles would mean modification in the soma, 

 but this modification would not appear in his child be- 

 cause only tlie germ cell is inherited, not the soma.^ 



Modifications of the so7na are of two kinds: ''first, 

 those produced by the effect of the environment upon 

 the organism ; and second, those resulting from the reac- 



8 Metcalf, 02). cit., j). 73. 



