40 THE AMERICAN NATURALIST [Vol. LIV 



suit finally obtained by the process described is that 

 which appears in Tables XII and XIII under ' ' ehdoderm. ' ' 



TABLE XIII 



Showing the Relative Influence of the Primary Germ Layers in 

 Human Mortality 



The data of Tables XII and XIII are shown graph- 

 ically in percentage form in Fig. 2. 



The final results shown in Tables XII and XIII lead at 

 once to a generalization of considerable interest and sig- 

 nificance to the evolutionist. The figures show that in 

 man, the highest product of organic evolution, about 57 

 per cent, of all the biologically classifiable deaths result 

 from a breakdown and failure further to function of 

 organs arising from the endoderm in their embryological 

 development, while but from 8 per cent, to 13 per cent, 

 can be regarded as a result of breakdown of organ sys- 

 tems arising from the ectoderm. The remaining 30 to 35 

 per cent, of the mortality results from failure of meso- 

 dermic organs. Taking a general view of comparative 

 anatomy and embryology it is evident that in the evolu- 

 tionary history through which man and the higher verte- 

 brates have passed it is the ectoderm which has been 

 most widely differentiated from its primitive condition, 

 to the validity of which statement the central nervous 

 system furnishes the most potent evidence. The endo- 

 derm has been least differentiated in the process of evolu- 

 tion, while the mesoderm occupies an intermediate posi- 

 tion in this respect. An elaborate array of evidence 

 might be presented on these points, but to do so would be 



