348 Evolution and Adaptation 



that in the egg of the snail. Zeleny has found a similar rela- 

 tion to exist for the big and the little opercula of the marine 

 worm, Hydroides. 



Let us consider now the more general questions involved 

 in these symmetrical and asymmetrical relations between the 

 organism and its environment. In what sense, it may be 

 asked, is the symmetry of a form an adaptation to its environ- 

 ment ? That the kind of symmetry gives to the animal in many 

 cases a certain advantage in relation to its environment is so 

 evident that I think it will not be questioned. The main 

 question is how this relation is supposed to have been attained. 

 Three points of view suggest themselves : First, that the form 

 has resulted directly from the action of the environment upon 

 the organism. This is the Lamarckian point of view, which 

 we rejected as improbable. Second, that the form has been 

 slowly acquired by selecting those individual variations that 

 best suited it to a given set of surrounding conditions. This 

 is the Darwinian view, which we also reject. The third, 

 that the origin of the form has had nothing to do with the 

 environment, but appeared independently of it. Having, 

 however, appeared, it has been able to perpetuate itself under 

 certain conditions. 



It should be pointed out that the Darwinian view does not 

 suppose that the environment actually produces any of the new 

 variations which it selects after they have appeared, but in so 

 far as the environment selects individual differences it is sup- 

 posed to determine the direction in which evolution takes 

 place. On the theory that evolution has taken place indepen- 

 dently of selection, this latter is not supposed to be the case ; 

 the finished products, so to speak, are offered to the environ- 

 ment ; and if they pass muster, even ever so badly, they may 

 continue to propagate themselves. 



The asymmetrical form of certain animals living in a sym- 

 metrical environment might be used as an argument to 

 show that the relation of symmetry between an animal and 





