44 University of California Publications in Zoology [Vol.19 



The table shows, in brief, that Eucalanus is positively geotropic 

 except when exposed to light from below. It is then strongly negative, 

 and we may suppose that the negative phototropism is stronger than 

 the tendency to move downward. 



The responses were not investigated in water of unusually Low 

 temperature or high salinity, so that it is not known whether the 

 phototropism and geotropism change as these factors are altered. 



The experiments have shown that Eucalanus is strongly negative 

 to light of low and of high intensity, and positive to gravity in diffuse 

 light, in darkness, and in light from above. It is negatively geotropic 

 in light from beneath. Since experiments are lacking to show whether 

 these reactions change with decreased temperature or when the salinity 

 is increased, it seems hardly worth while to discuss the bearing of the 

 experimental results on diurnal migration. It may not be out of 

 place to state that the reason for the few experiments with Eucalanus 

 is that the animals were obtained in such small numbers. Practically 

 all the individuals brought in were used. 



The results of an examination of the field records for Eucalanus are 

 available in two papers (Esterly, 1911a, 1912, pp. 295-300). The 

 data show that there are larger numbers of animals at the surface at 

 night, but it docs not appear that there is a well marked diurnal migra- 

 tion although there is an extensive movement below the surface. 



Reactions op the copepod Labidoccra trispinosum 



These animals have been extraordinarily abundant at times about 

 La Jolla, but during the academic year 1916-17 they were scarce. 

 The animals do not endure confinement in the laboratory very well, 

 and they do not usually remain in suitable condition even over night. 

 But if they were active on the second day after collection I did not 

 hesitate to use them. I have not found any reason to suspect that the 

 responses change after the animals are brought into the laboratory 



Labidoccra differs from the other copepods used in having well 

 developed eyes with prominent lenses. There are two on the dorsal 

 and oni- on the ventral surface of the head. 



The animals are rather slow swimmers as a rule, but if disturbed 

 they dart about with great rapidity. The movement is steady and lacks 

 the jerkiness of Calanus or Acartia, When swimming in a shallow 

 dish the course is wavering and uncertain but the animals keep mov- 

 ing steadily. In the narrower confines of a tube the course is prac- 



