360 STUDIES IN GENERAL PHYSIOLOGY 
the same relation to light in every particular as do the 
animals with the brain. If Lumbricus fcetidus 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 
photokinetic. 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 fcetidi 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 
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