iSiS] Esterly: Reactions of Various Plankton Animals 4."> 



tieally straight. The posterior antennae are in constant motion 

 whether the animal is ascending or descending in a vertical tube ; in 

 the latter case the appearance is something like that of a bird hover- 

 ing. I have seen no instances in which an animal sank immobile after 

 the fashion of Calanus. It is not uncommon for individuals to circle 

 in a vertical plane, and sometimes this behavior is kept up for a 

 good many minutes. 



PHOTOTROPTSM 



Labidoccra is negative to light. I have not tested them in a wide 

 range of intensities but the reactions are predominantly negative in 

 the dim light of a 15-watt lamp as well in that of the 50 by 40 cm. 

 window. Table 13 is a summary of the behavior of several animals in 

 a rectangular aquarium 20 by 8 cm. The vessel was marked off into 

 five sections, as usual, and turned end for end several times in the 

 course of an experiment. 



TABLE 13 



The Phototropism op Labidocera. Summary op Records of Several Sets of 



Animals in Light of North Windows; Temperatures 15°-20°C, 



Salinity 33 to 34 o/ 00 . 



Number of observations 



Whole Percentage distribution per 



number 



Table 14 is of the usual form that deals with the responses of 

 different individuals. The results of using different intensities of 

 light are put together in the table since most responses are negative. 



TABLE 14 



The Phototropism of Labidocera. Summary of Records of Individuals in 

 Light of Low and High Intensity. Temperatures 15°-20°C: 

 Salinity 33 to 34 "/,„,. 

 Records of position 



The results that appear in tables 13 and 14 are so evident that 

 comment is unnecessary. 



