EVOLUTION" AND ITS CONSEQUENCES. 25 



in different races of the same species of individuals of common 

 parentage, showing that they must have grown with the history 

 of those races ? Who does not know the short, wide jaws of the 

 bull-dog, with their oblique teeth, produced by the expansion of 

 the zygomata to accommodate the huge temporal muscles so neces- 

 sary for maintaining a firm hold of its enemy. Then the long and 

 full nose of the hound, and its more extended turbinate bones — 

 how closely is this connected with its developed scent ; while the 

 light muscular forms of the greyhound are undoubtedly necessary 

 to its well-known speed. If it be said that these variations have 

 not resulted in a single change of structure worthy of note by a 

 systematist, we can point to the Japanese dog, where the excessive 

 reduction of the jaws anteriorly has resulted in a total loss of some 

 of the premolars and molars. The loss of molar and incisor teeth 

 from shortening of the jaws, in the human species, has been al- 

 ready noted. The number of such instances is very great, but, as 

 space to enumerate them fails, it is only necessary to add that they 

 are characters of high importance in a systematic sense. Their 

 importance will be more readily conceded in remembering the 

 proposition, already stated, that species are simply isolated varie- 

 ties, and of similar origin. 



Confirmatory of this view are the facts already cited with ref- 

 erence to the relation of motive to growth-force. The force in- 

 volved in both being seen to be similar, perhaps identical, the 

 former represents its energetic state as discharge and motion, the 

 other energetic without discharge, in the growth of cells. And 

 whatever determines this force to a given part of the body must 

 then probably result in both of its exhibitions, dependent on the 

 kind of cells which receive it. As above remarked, the conditions 

 which determine the result are unknown, except that the two 

 kinds of muscular cells are the only ones in which elongation is 

 strongly marked. 



Another reason for believing in use as a cause of structural 

 change is the manner in which the same useful structures have 

 evidently appeared on totally distinct stems, as an evident adapta- 

 tion to the same circumstances in which the different types have 

 been equally placed. Thus the birds of prey possess the hooked, 

 often toothed, beak, appropriate for tearing and destroying ani- 

 mals. Their stock is the same as that of the cuckoos and parrots, 

 and even of the pigeons. The butcher-birds are of the division of 

 songsters, not widely removed from the thrushes, and far enough 



