Harper, Behavior of Corethra. 447 



collected them in ponds whose water was shallow and also con- 

 stantly quite turbid. In one pond whose greatest depth was four 

 feet they were fairly abundant. In another with a depth of 

 twenty-five feet they were very numerous. They could be 

 obtained easily from the surface waters near the shore line in the 

 daytime. Night was however the favorable time for collecting 

 them, as they then came to the surface in great numbers. It is 

 manifest that in the turbid waters of ponds they do not all seek 

 such depths in the daytime as is the case in the clearer waters of 

 some lakes. It is of course quite possible that the food supply 

 also has something to do with the depth to which they go. 



Experiment 2. — In order to determine the influence of light on 

 their downward movements the experiment was next tried of light- 

 ing the water from above. The larvae were placed in a tall cylin- 

 drical jar, on top of which was placed a dish of alum water. The 

 experiment was tried in a darkened room and the larvae were soon 

 distributed through the upper portion of the jar. A 32 candle 

 power bulb was then held over them. As soon as the light was 

 turned on they began to swim downward. After a few minutes 

 they had moved into the lower portion. All seemed to be aff^ected 

 by the light but in different degrees as indicated by the depths 

 assumed. In some lots the animals went upward toward the 

 electric light. There seemed to be differences in lots collected 

 at different times. 



Experiment J. — The jar was next lighted from underneath. 

 It was supported on a ring with a dish of alum water close beneath. 

 When the animals had remained in the dark long enough to move 

 upward the light was turned on beneath the jar. The larvae at 

 once moved downward as before and settled in the lower portion. 

 In both experiments some came to rest on the bottom. This 

 experiment indicates that the downward movement is not a nega- 

 tive light reaction, as the animals went toward the light. 



Experiment ./. — Experiments 2 and 3 were next repeated with 

 direct sunlight. For this purpose a cylmdrical screen of black 

 paper shaded the sides of the jar. In lighting from above the 

 direct light was allowed to enter as far as possible but this was 

 reenforced by reflection from a mirror. In lighting from beneath 

 the light was reflected upward from a mirror. The experiments 

 were carried on near a window where the rays were entering at a 

 high angle. The results were the same as in 2 and 3. The same 



