No. 630] 



HUMAN MORTALITY RATES 



4 1 



supererogation. It would amount simply to repeating 

 any standard treatise on the comparative anatomy of the 

 vertebrates, a branch of biological literature which one 





303 1 7 







WALES 1914- 







SAO PAULO 1917 



may fairly assume that the readers of this paper are 

 acquainted with, at least in general terms. 



Degree of differentiation of organs in evolution implies 

 degree of adaptation to environment. The writings of 

 Darwin and Spencer, and in current times of Henry 

 Fairfield Osborn, have demonstrated this point beyond 

 question. From the present point of view we see that 

 that germ layer, the endoderm, which has evolved or 

 become differentiated least in the process of evolution is 



