H4 Heredity and Social Progress 



envelope cause cells to become increasingly 

 complex by preventing that quick, complete 

 division characteristic of unicellular organism. 

 Differentiating division is little more than in- 

 complete division, by which parts readily 

 thrown off under simpler conditions are re- 

 tained and aggregated in ways least hostile 

 to further union. This tendency results 

 in increased complexity and differentiation so 

 long as growth is dominant. When, however, 

 the process has been carried so far as to make 

 the union unstable, or when the growth forces 

 slacken, the delayed divisions complete them- 

 selves, and some, at least, of the cells are 

 brought back to their original simplicity. 

 Germ cells are therefore not simple divisions 

 of the first cell, but are at the end of a curve 

 of development which in its first part becomes 

 increasingly complex, and in the latter part, 

 through devolution, regains the simple state of 

 the first cell. The germ cell, ready for fertili- 

 zation after the final reduction, is not then 

 a simple division of the ancestral germ, but is 

 the last stage of a devolution that separates it 

 from the parent organism. 



