SUMMARY OF EVIDENCE 79 



existing species. This similarity of structure appears 

 the more remarkable the more closely morphological 

 study of organisms is conducted. To use an obvious 

 illustration given by R. H. Lock, it is found that "in 

 the hand of a man, the paw of a dog, the wing of a bat, 

 and the paddle of a whale, almost identically the same 

 series of bones can be traced." The uses to which these 

 several members are put differ widely, but, as Lock 

 adds, "An obvious explanation is to be found in the 

 supposition that these parts have arisen by a divergent 

 modification of parts which were originally identical." ^ 

 Throughout each group of species certain correspond- 

 ing organs have been discovered which appear to be 

 biiilt in accordance with one general plan. Nor is this 

 all. Amid much divergence of organic functioning the 

 general laws of assimilation of food, of propagation, 

 and even of disease, are essentially the same; as is 

 illustrated by the success with which experiments upon 

 lower animals are employed as the basis of medical and 

 surgical treatment of human disorders. 



3. A third group of facts which suggests and con- 

 firms the evolutionary theory is found in the gradation of 

 organisms which appears within the several chief groups 

 of species. In each case a hierarchy of organic forms 

 appears, stretching all the way from seemingly undif- 

 ferentiated organisms up to the most highly organized 

 species. It is a reasonable inference from this that the 

 higher forms are most recent in origin, and have been 

 produced by a progressive differentiation of earher and 



^ Recent Progress, p. 31. 



