LIGHT REACTIONS OF TERRESTRIAL AMPHIPODS 349 



Circus movements were performed when specimens with one 

 eye blackened were made to travel under a glass plate. When 

 lying on the right side with the right eye blackened, the curve 

 would go toward the light. The creature seemed to be exceed- 

 ingly uncomfortable in this position, and would try to turn 

 over to the other side. When lying on the left side so that the 

 blackened eye was above, the curve would turn to the left, i.e., 

 toward the normal eye. This seemed to be a more comfortable 

 position, although here too, was a slight tendency to turn over. 

 This effort to turn from one side to the other was not mani- 

 fested in normal specimens. 



Effect of carbon-dioxide. — I put a dozen positive 0. traskiana 

 and a dozen O. pugettensis into a deep glass dish and filled it 

 with C0 2 . After the gas had been pouring in for about five 

 minutes, signs of exhaustion became manifest. The specimens 

 tended to aggregate anywhere in the dish. I constantly dis- 

 turbed the aggregations by shaking the dish. Every time they 

 were thus disturbed, they went towards the light without ex- 

 ception. After about twelve minutes of constant inpouring of 

 gas, they became lifeless. The O. pugettensis lay on their sides 

 or backs with their legs extended, apparently dead, while the 

 0. traskiana lay on their sides, some curled up as if in a death 

 feint, others with body and legs extended. I then shut off 

 the gas. In about two or three minutes, they began to revive. 

 Some went directly toward the light, others turned about a 

 few times in one spot, before starting for the light. I tried the 

 effect of CO 2 twice, on the same specimens within twenty-four 

 hours. The reviving reactions on the first day were rather 

 violent in appearance. For about two minutes they paid no 

 attention to the light, but ran helter-skelter over one another. 

 The largest pugettensis put his long antennae back close to 

 his sides, hunched up his body and jumped up and down in 

 one spot. On the second day, the reviving reactions showed 

 none of this violent activity, but they were strongly positive 

 at once. 



It seems that carbon dioxide in certain amounts produces a 

 stimulating effect. A. R. Moore found that Daphnia became 

 positive to ultraviolet rays when a small amount of CO 2 was 

 added to the water. Loeb made Gammarus pulex, which are 

 normally negatively phototactic, positive by adding small 



