KINETOGENESIS. 375 



ing progressive modification in time have also been 

 mainly accounted for on mechanical grounds. 



5. OBJECTIONS TO THE DOCTRINE OF KINETOGENESIS 



It has been objected that Neo-Lamarckians are 

 self-contradictory and illogical in their defense of the 

 doctrine of the development of structures by use, or 

 by motion. It is asserted that they believe that stimuli 

 of different kinds produce similar results, and that 

 stimuli of the same kind may produce different re- 

 sults. The charge that Neo-Lamarckians hold those 

 views is correct, but it is not correct to suppose that 

 they are illogical or self-contradictory. This criticism 

 is one of those generalities which will not bear exam- 

 ination, while the doctrine of kinetogenesis will bear 

 examination. 



Thus it has been experimentally shown that bone 

 irritation will produce both bone deposit and bone ab- 

 sorption, according to the degree of irritation. Mode- 

 rate irritation produces deposit, and greater irritation 

 produces absorption. Hence it is that both impact 

 and strain, or pressure and stretching, will elongate a 

 bone, by stimulating growth, if not excessive. We 

 have the illustrations in the elongation of ligaments 

 and cartilages and their ossification under stretching, 

 and the shortening of both in absence of use, from 

 which we may infer their lengthening under use. The 

 continued lengthening of the limbs and teeth of the 

 higher Mammalia, in the course of geologic time, is 

 an illustration of the effect of continued impact and 

 transverse strain ; while the lengthening of the limb 

 bones of the sloth, and of the tarsal bones of many 

 bats, is a consequence of longitudinal strain. 



