Influence of Environment on Animals 213 



chemical effects, which may miderlie the color aberration 

 observed by Fischer and other experimenters. 



It is important to notice that Fischer was also able to produce 

 aberrations through the application of narcotics. Wolfgang 

 Ostwald has produced experimentally, through variation of 

 temperature, dimorphism of form in Daphnia. 



IV. THE EFFECTS OF LIGHT 



At the present day nobody seriously questions the statement 

 that the action of light upon organisms is primarily one of a 

 chemical character. While this chemical action is of the 

 utmost importance for organisms, the nutrition of which 

 depends upon the action of chlorophyll, it becomes of less 

 importance for organisms devoid of chlorophyll. Nevertheless, 

 we find animals in which the formation of organs by regenera- 

 tion is not possible unless they are exposed to light. An 

 observation made by the writer on the regeneration of polyps 

 in a hydroid, Eudendrium racemosum, at Woods Hole, may be 

 mentioned as an instance of this. If the stem of this hydroid, 

 which is usually covered with polyps, is put into an aquarium the 

 polyps soon fall off. If the stems are kept in an aquarium 

 where light strikes them during the day, a regeneration of 

 numerous polyps takes place in a few days. If, however, the 

 stems of Eudendrium are kept permanently in the dark, no 

 polyps are formed even after an interval of some weeks; but 

 they are formed in a few days after the same stems have been 

 transferred from the dark to the light. Diffused daylight 

 suffices for this effect. Goldfarb, who repeated these experi- 

 ments, states that an exposure of comparatively short duration 

 is sufficient to produce this effect. It is possible that the light 

 favors the formation of substances which are a prerequisite 

 for the origin of polyps and their growth. 



Of much greater significance than this observation are the 



