1919] Esterly: Reactions of Various Plankton Animals 47 



for eight hours altogether and lot B for about eleven hours. But the 

 latter animals were in darkness from the sixth to the eighth hour and 

 were consistently and strongly negative and during that time twelve 

 observations of the distribution was made. If something connected 

 with the laboratory conditions affects the animals, it plainly does not 

 affect all in the same way. In spite of the differences it appears, 

 nevertheless, that there is a tendency for Labidocera to ascend in dark- 

 ness, and to descend in the light. 



Table 16 (p. 49) deals with the behavior as shown by the results 

 with individual animals, the table being a summary. The possible 

 effects of longer and shorter periods of confinement in the laboratory 

 are considered by separating the recorded results into two groups, 

 for both darkness and diffuse light. 



It must be said that the results appearing in table 16 are con- 

 fusing. Negative geotropism prevailed slightly in diffuse light among 

 animals that had been a shorter time in the laboratory (C), at least 

 so far as the actual swimming is concerned. The reverse is indicated 

 for animals that had been longer in the laboratory (D) ; all the per- 

 centages are in favor of positive geotropism. The results of tests in 

 darkness, so far as they go, show that there is prevailing positive geo- 

 tropism in animals that were in the laboratory from 1-3 hours. This 

 is also the case in the second line of the table except as regards the 

 distance covered, where the difference is strongly in the negative 

 column. It is well to note that the distance percentages show that 

 there is an upward movement in the dark of animals kept for the 

 longer time in the laboratory (compare lines B and D), but the records 

 of position do not show that. If lines A and C are compared it is 

 seen that the distance percentage shows upward movement in the 

 light, and this is also indicated by the differences in the percentage 

 of records that show change of position. 



In view of the discordant results in table 16, especially when they 

 are compared with table 15, it is difficult to know what to conclude as 

 to the geotropism of Labidocera in the abscence of directive light. 



In directive light. The tendency of Labidocera to move away from 

 a source of light is shown, I believe, by its behavior in a vertical tube 

 when a lamp is at the top or bottom. In the former case the responses 

 are negative to light and positive to gravity ; in the latter they are 

 negative to both. The facts are shown in table 17 (p. 49). Length of 

 time in the laboratory does not make any difference in the behavior ap- 

 parently, so all records are entered in the table. The source of light 



