38 University of California Publications in Zoology [Vol. 19 



distribution of the animals is summarized in the lower half of table 

 10. During the day they were in very dim diffuse light in the dark 

 room ; after dark the observations were made in the light of the 15-watt 

 lamp. During this second experiment another cylinder was set up, 

 identical with the other one and containing control animals from the 

 same collection. But the temperature was about 18° C throughout 

 the length of the control cylinder; otherwise the conditions were the 

 same in both. The distribution in the control may be dismissed by 

 saying that from 10:30 a.m. to 8:50 p.m. fifty-five observations were 

 recorded. On two occasions one animal was noted in the second section 

 from the bottom, but all the others were in the lower section through- 

 out the experiment. 



The results set forth in table 10 are more striking in the case of the 

 second experiment, especially when the behavior of the control animals 

 is considered. I believe that these experiments, in spite of the some- 

 what meager results, indicate the existence of a factor that must be 

 taken account of in connection with diurnal migration. The fact 

 that the upward movement in the laboratory does not take place except 

 when the animals have been in cold water is significant in view of the 

 temperature distribution in the sea. Table 10 shows that but a small 

 part of the animals moved upward, but I believe that this can be 

 accounted for in part at least. When the light is turned for observa- 

 tion after nightfall, the animals do not move at once ; the quiescent 

 period is long enough for one to note the distribution accurately. But 

 even when the observation is made quickly there is more or less dash- 

 ing around. Some dart down and others up, so that the distribution 

 is upset every time an observation is taken. These unavoidable com- 

 plications probably make the upward movement appear less extensive 

 than it really is. 



There is evidence, therefore, of a physiological rhythm in Calanus 

 as in Acartia. The animals ascend at a particular time of the twenty- 

 four hours but not during the period of daylight. 



SUMMARY 



(1) The phototropism of Calanus is predominantly negative at 

 ordinary temperatures, but it becomes markedly positive in water of 

 10° C and less. The reactions to light do not change when the salinity 

 is increased. (2) The geotropism is very strongly positive in diffuse 

 light and in darkness, and the behavior does not change with changes 

 in temperature and salinity. (3) When the light falls vertically from 



