FUNCTION AND FUNCTIONAL STIMULUS. 147 



tional stimulus. But it is incorrect to ascribe this fact to the 

 assumption that heredity may have fixed this character so far 

 that development of an eye now occurs in the absence of light. 

 For Loeb 1 has shown that it is very easy to prevent the develop- 

 ment of these eyes by a number of different means, such as 

 lack of oxygen, which is a non-specific, non-functional factor. 

 Moreover, it is not necessary to point out that the influence of 

 light on a photographic plate has never been considered to be a 

 case of functional adaptation, although the sensitiveness of the 

 plate to light is just as much response to a physical factor as is 

 the regeneration of Eudendrium or as might be the variation in 

 the rapidity of eye-regeneration which although not found in our 

 experiments, might possibly have occurred. 



The theory of functional adaptation complicates instead of 

 simplifying the problem. What we should emphasize is not 

 the fact that the result of the response to light is different in 

 the case of Eudendrium from what it is in the case of the regener- 

 ated eye or of the photographic plate, but the fact that these 

 three phenomena all possess a common basis. It is obvious 

 that all three are governed by the same laws, with which we 

 are familiar from our knowledge of physics and chemistry; but 

 these laws are free from such terms as function, functional 

 stimulus, or any other stimulus, or the principle of adaptation. 

 In order, therefore, to obtain a fertile method for attacking 

 the problems confronting us we must constantly bear in mind 

 the fact that the same laws expressed in the same terms can 

 explain both organic and inorganic phenomena. 



1 Loeb, J., "Heredity in Heterogeneous Hybrids," Jour, of Morphol., March, 

 1912, XXIII., i. 



