REACTIONS OF BRANCHIPUS TO EXTERNAL STIMULI 237 



down, and the lights turned off, they were always found at the 

 surface of the water. When the curtain was raised, and non- 

 directive hght admitted, they immediately went to the bottom. 

 Accordingly more critical tests were made of this apparent re- 

 versal of response to gravity. 



The glass cylinder was graduated into six 2.5 cm. divisions, 

 and filled with distilled water to the top of the first division. 

 A cardboard box of suitable size blackened on the inside, was used 

 as a cover for the cylinder. 



When the animals were placed in the cylinder in diffuse light, 

 they remained at or near the bottom, but when covered they rose 

 to the surface, in nearly every case. In a few instances, they stayed 

 at the bottom, once when the specimen was observed to be moult- 

 ing, and at other times when the animals were inactive for causes 

 not clear to me. They did not always rise the whole distance to 

 the surface, but as may be seen by a perusal of the record given 

 below, they did so in the majority of cases. The animals did not 

 often seem to swim down, when the cover was removed, but in 

 most instances they apparently sank passively to the bottom 

 The positions of the specimens, together with the time of covering 

 and uncovering, are shown in the following record : 



April 15, 1910. One male 



20. At bottom — covered 



25. Uncovered — at surface — dropped down immediately 



30. At bottom — covered 



35. Uncovered — in division 3; went to bottom immediately 



37. At bottom — covered 



42. Uncovered — at bottom — moulting 



April 18, 1910. Three males 



25. All at bottom — covered 



35. Uncovered — two at surface, one in division 1 — went down at once 



40. All at bottom — covered 



45. Uncovered — all at surface — went down at once 



48. All at bottom — covered 



53. Uncovered — all at surface — went down at once 



55. All at bottom — covered 



58. Two at surface — one in division 2 — went down immediately 



9:00. All at bottom — covered 



9:05. Uncovered — all at surface — went down at once 



