KINETOGENESIS. 381 



fact that the characters of bone structure admitted by 

 Mr. Gary to have had a mechanical origin appear in 

 the young before birth, is evidence that race characters 

 are produced, in other words, that they are inherited. 



Another objection proposed by Tomes, and quoted 

 by Poulton and Wallace with approval, has reference 

 to the kinetogenesis of teeth of Mammalia as described 

 by Ryder and myself. Tomes asserts that it is quite im- 

 possible that the crowns of the teeth could have been 

 altered by mechanical impacts and strains, since their 

 form is determined in the recesses of the dental grooves, 

 entirely removed from all the mechanical influences 

 which affect the external surfaces of the jaws. But 

 the observations of Koelliker and others show that 

 osteoclasts are as active in dental as in ordinary osse- 

 ous tissue. It is altogether probable that the modifi- 

 cations of dental structure have been produced by 

 strain and friction under use in the adult, precisely as 

 in the skeleton, and that the share that the unerupted 

 crowns have in the process is that of inheritance only, 

 as in the case of the skeleton. That teeth deposit den- 

 tine as process of repair in adult mammals is well 

 known, and this repair is in direct relation to use. 

 That the effects of dental wear are inherited is proven 

 by the fact cited by Tomes and Wallace. 



Another objection to the doctrine of kinetogenesis 

 which has been made by some of the Neo-Darwinians 

 is, that if growth under stimulus be true, how can it 

 have limits, so long as the stimulus of use exists. In 

 other words, what is to prevent, in the case of the 

 vertebrate skeleton, of an indefinite increase in the 

 length of the legs, of the teeth, and of their cusps, etc. 

 The answer to this objection will vary more or less 

 with the part of the structure considered. In general, 



