234 MARY O. McGINNIS 



Photoreceptors 



An effort was made to remove the eyes, in order to determine 

 whether any other part of the body is sensitive to Hght. The opera- 

 tion however, though very carefully performed, proved fatal to 

 the animals. Recourse was then made to covering the eyes 

 with an opaque cap of Canada balsam and lampblack. The speci- 

 mens were laid on a moist filter paper under a dissecting lens and 

 after the moisture had been removed as completely as possible 

 from the eyes, the balsam and lampblack were applied. The 

 operation was entirely successful with only two individuals. 

 These were returned to the water and allowed to recover. It was 

 found that they no longer responded to the light, but rose to the 

 surface and stayed there. The upward movement was not due to 

 the low specific gravity of the balsam, for animals which died with 

 the balsam on the eyes sank to the bottom. This reaction will be 

 discussed further under the account of the influence of gravity. 



We may conclude from these results that the eyes are the only 

 sense organs for the perception of light. 



BEHAVIOR WITH RESPECT TO HEAT 

 Reactions to increased and decreased temperatures 



In order to study the temperature reactions of Branchipus, 

 the large pan with black bottom and sides was placed under a 

 12 c.p. lamp, suspended from the ceiling of the dark room at such 

 a distance that the hght was practically uniform in its distribu- 

 tion, and hence had no directive effect upon the horizontal move- 

 ments of the animals. 



Ice was placed in one corner of the pan, and the temperature 

 reduced immediately under the ice to 8° C. The corner diagonally 

 across from this was heated to 30°. Seventeen animals were put 

 in at the warm corner, and in a short time they were distributed 

 as follows: seven in a region where the temperature was 16.5°, five 

 where the temperature was 17°, three where the temperature was 

 12°, and two under the ice in the region of 8°. There were none 

 in any region warmer than 17°. The animals did not remain 

 distributed in this way, but the greatest number moved about 



