OTHER THEORIES OF SPECIES-FORMING. 205 



natural selection," says Plate, "is capable of producing outer 

 adaptations such as making the fur of a mammal thicker 

 and thicker as a protection against the cold, why can it not 

 increase, or if advantage lies the other way, decrease, the 

 number of bony plates in the spongy tissue of the long 

 "bones ?" 



Second, the capacity of living substance to be stimulated 

 to increased food-getting is an elementary attribute of organ- 

 isms just as the capacities to assimilate, to be 



Trophic stimu- . _,..., 



lation not ex- irritable, and to breathe are. This special 

 plained. capacity is not explained by the theory of intra- 



selection; it is, indeed, just now wholly inexplicable. One 

 might perhaps fairly assume that it is the result of a gradual 

 development from the Protozoa onward, through the influ- 

 ence of individual selection. But this is no explanation of its 

 origin. Roux, himself, indeed, expressly declares that he 

 bases his theory on the proved but not explained fact of 

 functional adaptiveness, but some of his followers often 

 forget this and seem to claim that the distinctly advantage- 

 ous peculiarity of most tissues to be able to increase in 

 .strength and size through use is a direct result of the 

 battle of the parts. 



Third, Plate holds that the battle of the parts plays no 

 role in ontogeny. The cleavage and embryonal develop- 

 ment are wholly controlled by heredity, so that 

 parts not evident there is nothing left for the battle of the parts, 

 m ontogeny* There occurs a peaceful and regular split- 

 ting apart of the single cells and a separation of them 

 according to their different qualities, and it does not at all 

 occur that the strongest cells get all the food and the weak- 

 est none, but on the contrary each receives as much as it 

 needs for its growth. In a blastula of thirty-two cells it is 

 not the capacity on the part of certain cells which results in 

 the stronger growth of some and the weaker growth of 

 others, or the more rapid multiplication of some and the 



