HELIOTROPISM 59 



ends of the body bend ventrally with the body in emprosthotonus. The 

 head is bent far down. The animal may actually stand on its head, but 

 the abdomen retains its ventral curvature, leaving a considerable angle 

 open between its dorsuni and the wings which normally rest on it. 



In both walking and flying it continually keeps close to the table, 

 and upon encountering an obstacle it frequently does a forward somer- 

 sault. If it gets on its back it rights itself with greatest difficulty as its 

 efforts simply result in bending the tail and head ventrally until they 

 may form a complete ring. In galvanotropism the same general picture 

 is presented by Palcemonetes and Amblystoma when the anode is at the 

 head end, the tonus changes involved being identical in the two conditions 

 (Garrey 1 "). 



These experiments leave no doubt that the primary | 

 effect of light consists in changes in the tension of muscles 

 and that the heliotropic reactions which appeared to the 

 older observers as voluntary acts are in reality forced 

 movements. 



in the chapter on forced movements after brain lesion 

 the fact was mentioned that a dog which had shown circus 

 movements to the left after lesion of the left cerebral 

 hemisphere shows circus motions to the right when after- 

 ward the right hemisphere is injured symmetrically; in- 

 stead of being a physiologically symmetrical animal again 

 after the second operation. The explanation is that the 

 new operation is more effective than the old one whose 

 effect has partly worn off. Garrey has made an obser- 

 vation on heliotropism which shows some analogy with 

 this experiment on the brain. 



He found 177 that "robber flies with one eye black- 

 ened show the postural conditions in the most pronounced 

 way in the early morning or after being kept for some 

 hours in the dark. Constant exposure to the light pro- 

 duces considerable fatigue of the eye with recovery in 

 the dark. These facts among others suggested the possi- 



