DARWIN AND PALEONTOLOGY 



acter is a law unto itself, yet all subserve the gen- 

 eral good. For example, a new horn rudiment 

 arising on a brachycephalic skull will be broad 

 or rounded; if it arises on a dolichocephalic skull 

 it will be elongate or oval. Thus in a large quad- 

 ruped like a horse, a tapir, a titanothere, or a 

 rhinoceros each horn, each tooth, each bone of 

 the skull and skeleton, and by inference all 

 the hard parts as well as all the soft parts of 

 these animals in each phylum, have two sets of 

 relations : 



I. In the origin of new characters each phylum 

 will evolve, like other phyla, hypothetically 

 through inherited predispositions. Thus from 

 forty to forty-eight new characters will similarly 

 arise in a number of phyla in the grinding teeth 

 alone. 



II. In changes of proportion and in rate of 

 evolution each phylum will evolve unlike other 

 phyla, through freedom from hereditary predis- 

 position in matters of form, proportion, and rate 

 of evolution. 



These are the conclusions which I have reached 

 after twenty-two years of very precise work on 

 the evolution of the mammals. Besides exactly 

 observing primates, horses, rhinoceroses, during 

 the past seven years I have devoted myself to 

 still more precise monographic work on the group 

 of titanotheres, bringing together great quanti- 

 ties of material, and with the assistance of Mr. 

 W. K. Gregory making thousands of exact ob- 



