VIII PHYSIOLOGICAL RECRESCENCE 407 



until it gradually again impresses its own stamp upon its 

 neio'hbour." 



To my thinking, on the contrary, the recrescence of lost 

 parts falls under the same laws of acquirement and inherit- 

 ance as ordinary growth : it is nothing else but growth pro- 

 ceeding with increased vigour under peculiar conditions. 



How natural a process it is, and how justified we are in 

 asserting its subjection to the ordinary laws of growth, and 

 how dependent it is upon the contemporary condition of the 

 whole body, is excellently shown by the recrescence of the 

 horns of the Cervidee, and by the periodic renewals of hair 

 and feathers. These are instances, not of pathological, but 

 purely physiological recrescence, and examples of recrescence 

 in general than which none better can be conceived. In the 

 Cervidae, with the exception of the reindeer, the horns are 

 developed only in the males, and after castration they cease 

 to be developed in them. They develop according to per- 

 fectly definite laws every time they are renewed, becoming 

 more complicated every year : they grow. But this growth, 

 their normal recrescence, no longer goes on when the testes 

 are removed ; the horns degenerate and diminish with the 

 cessation of sexual activity. 



This example at the same time clearly exhibits the rela- 

 tion of recrescence to correlation, on which I have already 

 insisted. 



Eecrescence is only the increased action under special con- 

 ditions of a process which constantly goes on in our bodies as 

 long as we live. Like recrescence, the constant renewal of 

 the parts of the body, even of the highest animals, through- 

 out life depends upon acquired and inherited growth-tendency, 

 on acquired and inherited formative power. This renewal is 

 essentially nothing but a gradual process of recrescence. To 

 explain it, it is necessary to assume what I have assumed 

 for the recrescence of lost parts, and what all growth resulting 



