360 STUDIES IN GENERAL PHYSIOLOGY 



the same relation to light in every particular as do the 

 animals with the brain. If Lumbricus foetidus is introduced 

 into a transparent closed vessel it is noticed first of all that 

 the animals are strongly stereotropic. As soon as they reach 

 the concavity of a corner or a groove they crawl along it and 

 do not leave it. Secondly it can be shown that they are 

 photokiuetic. They come to rest in those regions which are 

 more weakly illuminated than the surrounding areas. The 

 direction of the rays of light is of little consequence. It 

 seems also as if, when one or more animals have come to rest 

 at any point, the others also come to rest at the same place 

 more readily. This looks as though the animals were "social." 

 This may be attributed to a chemotropic irritability. 



It is noteworthy that the less refrangible rays which pass 

 through red glass are less active for photokinetic animals 

 than the more strongly refrangible rays which go through 

 blue glass. The angleworms come to rest sooner under red 

 glass than under blue glass. (We can speak of a "prefer- 

 ence" for red light for this case just as little as in the case 

 of heliotropic animals.) Decapitated Lumbrici foetidi all 

 show the same stereotropism as normal animals. When they 

 reached the concave side of the corner of a vessel they did 

 not readily leave the corner again. The decapitated animals 

 also came to rest as did the normal animals in those regions 

 where the light was least intense, while an increase in the 

 intensity of the light stimulated them to movement. It 

 could also be shown that the light which passes through blue 

 glass acted in this regard as light of a greater intensity than 

 that which passes through red glass. 



In all these experiments the decapitated pieces crept 

 about with their tail end forward as well as with the oral end 

 forward. I noticed repeatedly a fact which shows that even 

 the extreme caudal end of the angleworm is sensitive to light. 

 For when the caudal end suddenly entered an illuminated 



