ORGANIC EVOLUTION — ^THE FACTORS 79 



greater number of them, so, in some cases, helping it 

 to conquer and survive. Among its descendants, in- 

 heriting the modification and the accompanying habit, 

 the thickening would be further increased in the same 

 way — survival of the fittest tending ever to accelerate 

 the process. Presently the horny nodes thus formed, 

 hitherto defensive only in their effects, would by their 

 prominence become offensive, would make the blows 

 given more hurtful. And now Natiu-al Selection, aid- 

 ing more actively, would mould the nodes into spurs ; 

 the individuals in which the nodes were most pointed 

 would be apt to survive and propagate ; and the pointed- 

 ness, generation after generation thus increased, would 

 end in the well-adapted shape we see." 



But on page 274 he says — 



" Besides ascribing to Natural Selection the rise of 

 various internal modifications of other classes than those 

 above, we must ascribe some even of these to Natural 

 Selection. It is so with the dense deposits which form 

 thorns and the shells of nuts : these cannot have 

 resulted from any inner reactions immediately called 

 forth by outer actions, but must have resulted medi- 

 ately through the effects of such outer actions on the 

 species." 



But if the accumulation of inborn variations is 

 considered sufiicient to account for the indurated 

 tissues which form the shells of nuts and the thorns of 

 plants, it is difficult to understand why it should be 

 considered insufficient to account for the indurated 

 tissues on the knuckles of the gorilla and on the 

 wings of the Chaja screamer. The transformation of 

 structures which were totally different into shells and 

 thorns appears at the least to furnish as extreme 

 examples of evolution as callosities and spurs, which, 

 after all, are only specialized thickenings of the 

 epidermis. As regards the gorilla, Mr. Spencer 



