326 Adaptation to Environment 



week or two in sunlight and in a dark room where 

 they were exposed to red incandescent light, two males 

 formed somewhat larger eyes. The first year no altera- 

 tion was visible. In the second year a slight increase 

 in the size of the eyes was noticeable under the skin. 

 In the third year the eye protruded slightly and this 

 increased somewhat in the fourth year. 



There is thus far only one case on record in animal 

 biology in which the light influences the formation of 

 organs. The writer found that the regeneration of the 

 polyps of the hydroid Eudendrium does not take place 

 if the animals are kept in the dark, while the polyps 

 will regenerate if exposed to the light ; * and the time of 

 exposure may be rather short according to Goldfarb. 2 

 It is possible that Proteus resembles in this respect 

 Eudendrium; it should be stated, however, that of 

 many different forms tried by the writer over a number 

 of years, Eudendrium was the only one which gave evid- 

 ence of such an influence of light. Of course it is not 

 impossible that the light might influence reflexly the 

 development of blood-vessels in the eyes of certain 

 animals, e. g., Proteus, and thus allow the eyes of Proteus 

 to grow a little larger. 



We therefore come to the conclusion that it is not 

 the cave that made animals blind but that animals with 

 a hereditary tendency towards a degeneration of the 



* Loeb, J., Arch. d. f. ges. Physiol., 1896, briii., 273. 



2 Goldfarb, A. J., Jour. Exper. Zool., 1906, iii., 129; 1910, viii., 133. 



