324 Journal of Comparative Neurology and Psychology. 



the general fact that circumstances which reduce the excitabili- 

 ty of the insect tend to produce the negative reaction. 



6. Phototaxis Leading to Fatal Results. Wishing to ascer- 

 tain if Ranatra would continue to be positively phototactic if it 

 were thereby led into a situation which exposes it to stimuli 

 having injurious, if not fatal, effects I performed the following 

 experiment. 



A strong arc lamp was placed on a table so that the focus or space between 

 the carbons was about five inches from the top, this elevation being chosen so 

 that the specimen could not walk directly into the luminous arc although it was 

 free to move about beneath it. As the lamp gave out a large amount of heat the 

 insect in approaching the focus would he brought into a region sufficiently heat- 

 ed to produce a fatal effect if it remained there long. A Ranatra placed on the 

 table, moved toward the light until it came under the focus, then starting off 

 again, only quickly to return. It soon became wildly excited and made repeated 

 dashes toward the light. Several times it flew towards it, but luckily escaped 

 coming between the carbons. After a time it gave signs of being overcome with 

 the heat, but whenever removed from the light it would quickly return. Its 

 movements became weaker, although its efforts to go to the light were no less per- 

 sistent. It became unable to raise its body off the top of the table as it walked, 

 but used its legs to slide its body towards the light, and it would quickly re-orient 

 itself when placed obliquely to the rays. Even its very last piteous efforts were 

 devoted to pushing its body a little nearer the light. When no longer able to 

 move it was placed in cool water, but it did not revive. 



When a moth flies into a flame it is probably because it 

 does not have time to check or change the course of its flight 

 after it has drawn near enough to experience the injurious effects 

 of the heat. The suicidal conduct of Ranatra, however, cannot 

 be accounted for in this way. The movements of the insect 

 are slow and deliberate enough, especially when it becomes 

 weakened, so that it need not be carried by its momentum into 

 a region from which it would otherwise flee. It reacts positive- 

 ly at every step, even when nearly overcome by the heat. 

 Essentially the same phenomenon is seen in Talorchestias which 

 when exposed to direct sunlight, keep jumping towards the 

 light until the heat overcomes them and they die. 



7. Inhibitiofi of Phototactic Responses by other Activities. 

 The phototactic responses of Ranatra which usually occur with 

 such regularity and precision are sometimes checked when the 

 insect is engaged in performing some other function. Speci- 

 mens that have been following the lieht for some time often 



