Holmes, TJie Reactions of Ranatra to Light. 323 



li. It takes place independently of differences of temperature, 

 and it cannot be satisfactorily accounted for by attributing it to 

 chemical or osmotic changes produced by the surrounding 

 media. Anything which makes towards the peculiar nervous 

 condition which accompanies the death feint tends to produce 

 the negative response. Dipping Ranatras into water usually 

 throws them into condition of quiet when other influences fail, 

 and the negative reaction is doubtless a result of the nervous 

 state thus brought about. When a Ranatra is either placed in 

 the water or removed from it, every portion of the surface of 

 the insect is stimulated, and, although the stimulus upon no 

 part is strong, the general effect may well be considerable. 

 That the general integument is very sensitive is indicated by 

 the fact that decapitated specimens often respond very strongly 

 to the slightest breath of air. 



5. The Effect of Temperature on Photoiaxis. Raising the 

 temperature tends to accentuate the positive phototaxis in Ran- 

 atra and lowering it tends to produce the negative reaction. In 

 several experiments two dishes containing Ranatras were set 

 before a window so as to receive the same amount of light. As 

 the specimens had been previously kept in the dark, they show- 

 ed a negative reaction. Into one dish warm water was poured 

 raising the temperature from about 20° C to nearly 30° C. In 

 a few minutes the specimens in the warmer dish became posi- 

 tive, the ones in the cool water still showing a negative photo- 

 taxis. Ranatras transferred to the cooler dish soon became 

 negative while those which were picked up in the same way 

 and dropped back into the warm water from which they were 

 taken soon resumed their positive reaction. On the other hand, 

 transferring negative specimens from cool to warm water pro- 

 duced in a short time a positive response. In cool water there 

 is a marked tendency to form a dense cluster in the negative 

 end of the dish. In warmer water the insects become more 

 active and the groups are more apt to be broken up. Water 

 at a temperature of 30° C usually stimulates them to very ener- 

 getic movements. That negative phototaxis in Ranatra is in- 

 duced by a reduction of temperature affords an illustration of 



