DARWIN^S THEORY 79 



seeking room. In most cases, alas ! the colonists perish, but 

 once in a long while they manage to establish themselves and 

 thus a new race comes into being. The incursion into new 

 territory seems to occur in the majority of cases in the 

 adolescent stage; the younger stages of growth being passed 

 through in the mother country : these younger stages then con- 

 stitute a larval phase. Now in response to the new environ- 

 ment the structure of the latest stages becomes altered and 

 that adult structure is capable of alteration under the stress of 

 new circumstances is a well-known fact but we are bound to 

 assume that this change of structure has in time become trans- 

 ferred from the body (soma) to the germ-cells, so that these 

 now have acquired the tendency to develop the new type of 

 structure at earlier and earlier periods in the life-history and 

 quite independently of the stimulus of the new environment. 

 Thus the recapitulatory theory, which is an inevitable deduc- 

 tion from the general theory of evolution, is calculated to 

 throw in turn considerable light on the nature and origin of 

 inheritable variation. The tendency of the Mendelian school 

 to regard the properties of the germ-cells as being as unalter- 

 able as those of the chemical atoms is certainly in direct 

 contradiction to the impression gained by a comprehensive 

 survey of the life-histories of animals. 



If we use the weapon which the recapitulatory interpretation 

 of enbryology puts in our hands, and explore what the actual 

 course of evolution within the great phyla has been, we seem 

 to see that in each phylum Nature has striven after the elabo- 

 ration of some organ or group of organs which have been 

 dominating factors in the life of members of the phylum. To 

 take the most familiar instances : amongst carnivorous mammals 

 the teeth and claws are the all-important things, and so we 

 find in tigers the great eye-teeth enlarged into formidable 

 spears, whilst the back teeth are reduced to one or two pairs 

 of powerful scissors ; the claws are bent back when not in use 

 so that their points may not be worn down, and the animal 

 walks on the hairy second joints of its fingers and toes (the 

 well-known " furry " paw of the cat). Various kinds of cat- 

 like animals are classified by the degree of perfection attained 

 by teeth and claws. 



Amongst hoofed animals or Ungulata the teeth, hoofs, and 



