Holmes, Tlie Reactions of Rajiatra to Light. ^ly 



The specimen was then exposed to the strong light from a projection lantern. It 

 showed at first a weak positive phototaxis which grew stronger the longer it was 

 exposed, until it finally became almost violent. When exposed to the much 

 weaker illumination from a i6 candle power lamp it still showed a marked posi- 

 tive phototaxis, but not so strong as when exposed to the light of a projection 

 lantern. 



At another time a Ranatra was placed in the trough which was exposed to 

 the light of an incandescent lamp placed two feet from one end. The specimen 

 immediately swam to the negative end of the trough. When the lamp was 

 placed two feet from the other end the specimen quickly returned. The light 

 was then changed repeatedly several times and each time the Ranatra would 

 swim to the negative end of the trough, usually within four or five seconds. 

 After a time its responses became slower and less definite. The light was then 

 held close to the end of the trough and the responses became as prompt as before. 

 It was changed from one end of the trough to the other forty-two times, and 

 each time the insect within four or five seconds went to the negative end. Then 

 it was left several minutes, after which its negative responses became less marked. 

 When it was exposed to the strong light of a projection lantern it was still nega- 

 tive. It was then taken out of the water and laid on the table. In a few min- 

 utes it came out of its feint and showed the usual swaying movements when an 

 incandescent lamp was moved near it, but it was very reluctant to walk. After 

 15 minutes of hesitation it became more active and showed an unmistakable posi- 

 tive reaction, and several times flew towards the light. When placed in the 

 water again it still showed a strong positive phototaxis. The next morning 

 (it was not in the meantime exposed to light, the room being darkened) it was 

 markedly negative, and was driven from one end of the trough repeatedly by 

 changing the position of the light. Then it was taken out of the water and 

 placed on the table and an incandescent lamp was moved about near it to bring 

 it out of its feint. It was a long time in awakening and for several minutes 

 afterward it was disinclined to walk. When it did so it began to follow the light 

 and soon became so excited that it would fly towards it repeatedly when four or 

 five feet away, When put back into the water it was still positive and would 

 follow the light in every direction. It was then exposed to the light from a pro- 

 jection lantern and became more strongly positive than ever, moving wildly 

 towards the light even in the intense glare of the focus. Brought back to an 

 incandescent lamp again it showed only a comparatively feeble response. 



The negative reaction is associated with a condition of low- 

 ered phototonus. It is rarely shown except when the animal is 

 in a condition of comparative sluggishness. When in great 

 excitement, when its movements take place with quickness and 

 vigor, Ranatra always shows a positive response. It never flies 

 away from the light. Whenever it is wrought up sufficiently 

 to use its wings, its reaction is invariably positive. The nega- 

 tive movements are slow and stealthy, often giving one the 

 impression that the insect is attempting to sneak away unob- 



