Tropisms Relation to Modes of Behavior 59 



It will be of interest in this connection to consider 

 the light reactions of a somewhat more highly or- 

 ganized arthropod, the water scorpion Ranatra. 

 This insect lives near the banks of ponds and streams 

 with the tip of its long breathing tube at the sur- 

 face of the water and its raptorial fore legs held 

 in a position for rapidly seizing any small passing 

 creature which may be utilized for food. When 

 Ranatra is taken out of the water it generally feigns 

 death, assuming a perfectly rigid attitude which it 

 retains through all sorts of maltreatment, even suf- 

 fering its legs to be cut off or its body to be cut in 

 pieces without betraying any signs of animation. By 

 moving a light over the motionless insect it may 

 gradually be brought out of its feint. The first no- 

 ticeable signs of awakening are very slight move- 

 ments of the head in response to the movements of 

 the light. When the light is passed to one side of 

 the body the head is rolled over ever so little toward 

 that side. Move the light to the other side and 

 the head tilts over slightly in that direction. Place 

 the light in front of the body and the head bows 

 down in front. Now carry the light behind the in- 

 sect and the front of the head points slightly up- 

 ward. These movements occur with perfect regu- 

 larity in response to the movements of the light, 

 and gradually increase in vigor and extent. After 

 following the movements of the light with these 

 definite movements of the head the insect slowly and 

 awkwardly raises itself up and begins to follow the 



