142 THE INFANCY OF ANIMALS 



vomer, while in others they just fall short of touching, 

 as in our illustration. And now a curious thing takes 

 place. The forwardly directed spike of the pterygoid, 

 to which we have referred, rests upon the upper surface 

 of the palatine, and in due course becomes separated from 

 the main shaft, almost as if by fracture, just behind the 

 end of the palatine. Next the fractured end fuses with 

 the palatine, so that its identity is completely lost, and 

 thereafter the cup-and-ball joint forms, apparently between 

 the palatine and pterygoid, but really between the hinder 

 end of this fused segment of pterygoid and its larger 

 moiety. When we come to examine a large series of 

 different types of birds, we find this spike-like anterior end 

 of the pterygoid growing smaller and smaller ; in some 

 only a mere nodule of bone appears, in others even this 

 is wanting. And the same is true of the vomer. In the 

 hawk tribe, for instance, there is a more or less distinct 

 " hemipterygoid," but this has vanished in the falcons. 



Surely a more interesting illustration of the stages 

 whereby new types of structure are evolved it would 

 be hard to find anywhere. Huxley was, rightly enough, 

 impressed by the profound difference which obtains 

 between the palatal region of the ostrich tribe and those 

 of all other birds ; and he of all men would have appreciated 

 to the full the facts revealed by a study of the skulls of 

 nestling birds, if only chance had happened to start his 

 curiosity in this direction. No more striking demonstra- 

 tion could be found of the contention that animals, in 

 the course of their individual development, or " ontogeny," 

 repeat the history of their race. 



It is difficult for the layman, for obvious reasons, to 

 examine such facts as the foregoing for himself, or even, 

 perhaps, to appreciate their full significance — at any 



