EXPERIMENTS ON WORMS 89 



for this reason they become quiet when in contact 

 wifr.h a worm of the same species. These chemical 

 stimuli act as a trap, just as the comparative minimum 

 in the intensity of the light acts. It should be noted, 

 in this connection, that when animals are sensitive to 

 differences in the intensity of light, the less refractive 

 rays which pass through red glass have less effect 

 upon them than the more refractive rays which pass 

 through blue glass. The earthworms become quiet 

 under red glass sooner than under blue glass. 



How do decapitated earthworms act ? Decapitated 

 Lumbrici fcetidi show the same stereotropism that 

 normal worms show. When they reach the concave 

 angle of a vessel, they have no inclination to leave it 

 again. They also show the same response to light. 

 They rest in those places where the intensity of the 

 light is relatively weakest, and they move when the 

 intensity of the light is increased. It can also be 

 shown that light passing through blue glass acts like 

 light of greater intensity, while light passing through 

 red glass has the effect of light of weaker intensity (2). 



In all these experiments the decapitated pieces 

 crawl about with either the tail or the anterior end 

 in front. 



It is an interesting fact that the reaction-time when 

 light is the stimulus is not appreciably greater in de- 

 capitated than in normal earthworms. The animals 

 used for the experiment were in a box in which they 

 could be exposed to diffused daylight suddenly with- 

 out being jarred. In from three to eighteen seconds 



