4ii 



University of California Publications in Zoology [Vol. 19 



GEOTROPISM 



In darkness and diffuse light. It is difficult to know what to say 

 about the geotropisru of Labidocera. There is a good deal of difference 

 in the behavior of different sets of animals. I used two sets of indi- 

 viduals. Lot A was obtained at 8 a.m. at the surface and had been 

 in the laboratory six hours before the experiment began. Lot B was 

 obtained in a vertical haul from about 60 meters at 9 a.m. and had 

 been in the laboratory about two hours. Except for these differences 

 the treatment and surroundings of the two sets were similar. Table 15 

 summarizes the observations on the distribution of the two sets in 

 darkness and in diffuse light. 



TABLE 15 



The Geotropism of Two Sets op Labidocera (A and B) in Diffuse Light and 

 in Darkness. Temperatures 15°-18°C, Salinity 33 to 34 o/ 00 . 



Number of observations 



The table shows that in darkness the animals of lot A were strongly 

 positive in geotropism while those of lot B were even more strongly 

 negative. In diffuse light lot A was very strongly positive and lot B 

 predominantly but not markedly negative. Yet it is shown that with 

 each set there is an upward movement in the dark. The totals of the 

 percentages in sections IV and V are larger for both A and B in the 

 first two lines of the table than in the last two lines, and those in 

 sections I and II are smaller in the first two than last two lines of 

 the table. The centers of distribution, likewise, show that there is 

 ascent in darkness. Yet the two sets of animals are significantly 

 different in behavior if the distribution in darkness or in diffuse light 

 is considered alone It is upon comparison of the distribution under 

 one condition with that under the other that the movement is indicated. 



It does not seem that retention in the laboratory will account for 

 the difference in the two sets of animals. Lot A was in the laboratory 



