So THE COURTSHIP OF ANIMALS 



lower border of the jaw which are embraced by these 

 teeth. In the Sabre-toothed Tiger the inciting cause 

 to this flange growth, whatever it may have been, seems 

 to have been much weaker than in the case of Dinoceros. 

 Naturally one asks, can the whole thing be explained 

 by the theory of Kinetogenesis promulgated years ago by 

 Cope ? That is to say, are these curious downgrowths 

 the result of a response to a stimulus set up in the lower 

 jaw by constant lateral blows dealt by the tusks against 

 the side of the jaw during the lateral movements of the 

 jaw when feeding or ruminating ? Such movements in an 

 Ungulate would be frequent and constant : hence perhaps 

 the more striking result. On account of the scissor-like 

 action of the jaws in the Sabre-tooth such lateral move- 

 ments were far less extensive, and less powerful. But 

 though this explanation sounds plausible, it presents 

 many difficulties. In the first place it seems to commit 

 one to the admission that the responses of the Somatoplasm 

 during the life of the individual are transmitted to the 

 germ-plasm : that, in short, the characters acquired 

 by the individual during its lifetime are transmitted 

 to its offspring. And there are insuperable difficulties in 

 the way of such a theory. Yet, it must be admitted, 

 it is no less difficult to beheve that this correlation of 

 growth is due solely to fortuitous variation, for one 

 cannot really conceive of a variation of this kind taking 

 place in two such different structures independently. Such 

 a conception would have been less difficult if the case of 

 Dinoceros alone were known to us. We could have sup- 

 posed that, somehow, the lower jaw started to produce 

 its flange just as the teeth began to develop an excess of 

 growth which carried their points beyond the level of 

 the jaw. But the Sabre-tooth shows that the tusks 



