124 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



modifications which suggest that the relation in the ten- 

 sion of the antagonistic muscles of its legs is changed. 

 The animal turns out for obstacles that come in its 

 way. If a beetle that has lost the supraoesophageal 

 ganglion is thrown into water it swims off, drawing in 

 the first pair of legs. The normal water-beetle rests 

 quietly under dark objects. The water-beetle whose 

 supraoesophageal ganglion has been divided by a 

 longitudinal incision no longer shows these reactions, 

 although the light is still able to produce other effects 

 in the animal. If suddenly exposed to strong light 

 or a dark shadow when in motion, namely it ceases 

 to move. 



An animal whose right cesophageal commissure has 

 been severed does not brace itself against obstacles as 

 strongly with the legs of the right side as with those 

 of the left side. It seems to me this shows that the 

 extensors of the right side are weakened, as it is they 

 that have to perform the task of bracing. Further- 

 more, the right legs are moved constantly. It may 

 be possible that these two facts are in some way con- 

 nected. The decreased opposition of the extensors 

 renders the pendulum-movements of the legs easier. 

 The same explanation may hold for Astacus, bees, etc. 

 If the supra- and subcesophageal ganglia be extirpated, 

 the animal only makes progressive movements when 

 stimulated. But the ability to perform coordinated 

 progressive movements is not destroyed. When laid 

 on its back the animal still tries to regain the ventral 

 position, but the efforts made by the legs are vain. 



