EXPERIMENTS ON AR THRO PODS 1 1 9 



When these animals from which the brain has been 

 removed are laid on their backs they return to the 

 ventral position. 



The observations made by Bethe in crayfish in 

 which he had severed the cesophageal commissures 

 on only one side are interesting. The division was 

 made on the right side. If he touched the left side of 

 the head of such an animal, first the forceps of the 

 stimulated side reached toward the stimulated spot 

 and then those of the other side followed with accur- 

 acy. At the same time, the animal attempted to escape 

 backwards. If the same stimulus was applied to the 

 right side of the head, the forceps did not react. Even 

 with a strong stimulus no reaction followed. Hence 

 the stimulus that produces the localising reflex can only 

 be transmitted through the longitudinal commissure of 

 the same side to the appendages. This seems to hold 

 good generally for the Arthropods, since Bethe was able 

 to prove it in Carcinus, Squilla, and Hydrophylus. It 

 seems to hold good not only for the conduction through 

 the cesophageal commissures but through all longitu- 

 dinal commissures. After division of an cesophageal 

 commissure, circus-motions often but not always occur 

 toward the normal side. The animal is also able to 

 move straight ahead, but this requires some effort. 



If the right cesophageal commissure be severed, the 

 tonus of the muscles on the right side (the injured 

 side) of the abdomen is diminished, and as a result 

 the abdomen is curved toward the left and becomes 

 concave on that side. 



