HELIOTROPISM 59 



ends of the body bend ventrally witb tbe body in emprosthotonus. The 

 bead ns bent far down. Tbe animal may actually stand on its bead, but 

 tbe abdomen retains its ventral curvature, leaving a considerable angle 

 open between its dorsum and tbe wing's which normally rest on it. 



In botb walking and Hying it continually keeps close to tbe table, 

 and upon encountering an obstacle it frequently does a fox-ward somer- 

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

 efforts simply result in bending tbe tail and bead ventrally untU tbey 

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

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

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

 (Garrey 177 J. 



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- 



