40 A. M. REESE 



in the near half of the aquarium to 212 in the far half. It is 

 noticeable, however, that in the 16 observations before the 

 warm water was added 67 animals faced the light to 83 that 

 faced in the opposite direction, while in the 13 observations 

 after the addition of the warm water 67 animals again faced the 

 light but only 64 faced away from it. Again, in the first 16 

 observations 50 animals were counted in the near half of the 

 aquarium to 126 in the far half, while in the last 13 observations 

 57 animals were in the near half to only 86 in the far half. 



Experiment XI. — This was a continuation of experiment X 

 on the following day. The water at starting was 5.5° C. and 

 was raised, after observation 12 to 23° by the addition of 

 warm water. The first 7 observations were at somewhat irreg- 

 ular intervals of ten minutes; the remaining observations were 

 at five-minute intervals. In 30 observations 149 animals faced 

 the light to 154 that faced in the opposite direction; while 143 

 were noted in the near end to 198 in the distant end. In the 

 first 12 observations, however, when the maximum temperature 

 of the water was 11°, only 43 animals faced the light to 73 

 that faced away from it; while in the last 18 observations, when 

 the water had been raised to 23°, 106 animals faced the light 

 to 62 that faced the other way. Again, in the first 12 obser- 

 vations 48 animals were in the near half to 94 in the far half, 

 while in the last 18 observations the numbers were 95 to 104 

 respectively. In a total of 98 observations for the last three 

 experiments, 405 animals faced the light to 532 that faced in 

 the opposite direction; and 390 animals were counted in the 

 near half of the aquarium to 676 that were found in the far half. 



From the last three experiments it seems that low tempera- 

 tures tend to inhibit or even reverse the positive phototaxis 

 of Diemyctylus as seen in movements towards the light and 

 orientation of the body so that the animal faces the light. 



Experiment XII. — This experiment was to determine the 

 responses of Diemyctylus to white lights of different intensities 

 acting simultaneously at opposite ends of the aquarium. 



Nine of the same animals used in the preceding experiments 

 were employed here; they had been in darkness for 15 days. 

 The same aquarium in the same dark room was used; it was 



