48 University of California Publications in Zoology [Vol.10 



was the 15-watt lamp. It was placed about ten centimeters from the 

 top or bottom of the container, which was in most cases a tube 500 

 by 30 mm. 



So far as the observations that are summarized in table 17 are 

 concerned it is evident that Labidocera ascends or descends depending 

 on the location of the light. 



SUMMARY 



The experiments show: (1) That Labidocera is negatively photo- 

 tropic at ordinary temperatures. The responses are negative to light 

 of low as well as of high intensity. (2) The results concerning geo- 

 tropism are confusing. Table 15 shows that there is a tendency to 

 ascend in darkness and to descend in diffuse light on the part of 

 specimens that had been in the laboratory for ten hours at the most. 

 In table 16 it appears that there is a tendency toward negative geo- 

 tropism in diffuse light when the specimens had been in the laboratory 

 from one to six and a half hours; but those not tested for twelve to 

 twenty-seven hours after removal from the sea show positive geo- 

 tropism. Two individuals that were tested in darkness within one to 

 three hours after they were taken from the ocean showed positive geo- 

 tropism; others, not used until twelve to twenty-six hours after cap- 

 ture, gave uncertain results. (3) In directive light from above the 

 geotropism is strongly positive ; in directive light from below it is 

 strongly negative (table 17). 



POSSIBLE BEARING OF THE EXPERIMENTS ON DIURNAL 

 MIGRATION 



Since there is nothing to show whether the behavior changes when 

 the temperature is lowered or the salinity increased, a full discussion 

 of the relation between the results in the laboratory and the natural 

 habit is not possible. 



So far as the experiments are concerned, it is not to be expected 

 that Labidocera will occur at the surface during the day since it is 

 negatively phototropic and positively geotropic when the light is 

 from above ; also the field data show that this copepod is very much 

 more abundant at the surface from 6-8 p.m., and that it is practically 

 absent at other times (Esterly, 1912, pp. 307-309). The upward 

 movement of some sets of experimental animals when in the dark 



