94 Studies in Animal Behavior 



reached the movements of the insect are no longer 

 definitely controlled. The flies tumble and whirl 

 about in an irregular way, but in no case do they 

 show a negative reaction. 



There are other cases in which the power of re- 

 versal occurs, but where it is not brought into play 

 when it would seem to be most needed. The large 

 terrestrial amphipod or sand flea Talorchestia lonai- 

 cornis is ordinarily positive in its reactions to light. 

 When first exposed, especially if it is wet or cold, 

 it may show a vacillating tendency toward the nega- 

 tive reaction, but in strong light, especially in a 

 higher temperature, it becomes strongly positive. I 

 have exposed specimens in a dish one end of which 

 was shaded, while the other was illuminated by 

 direct sunlight. In the strong light they became more 

 strongly positive and persisted in attempting to 

 jump toward the light until they were overcome 

 by the heat and died in a heap at the end of the 

 dish toward the sun. Both the intense light and 

 the heat had the effect of rendering the positive 

 reactions of the creatures more decided. 



Similar behavior is shown by the water scor- 

 pion Ranatra when it persists in going toward a 

 powerful electric light until overcome by the heat. 

 Such behavior is certainly the reverse of adaptive. 

 Nature has not equipped the Talorchestias and the 

 Ranatras with any method of properly meeting a 

 situation presented by a combination of strong light 

 and a fatal degree of heat. Such combinations are 



