DAILY MIGRATIONS OF COPEPODS. 
109 
the tube were numbered from the bottom up, I to V, and the records were taken at 
the ends of five-minute intervals till ten records were obtained. The results are 
indicated in Table 1, where it appears that in eight records out of ten all five animals 
were in the uppermost section, and that in two records one animal in each case had 
descended to the fourth section: 
Table 1. 
Five-minute 
intervals. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
Totals. 
V 
5 
5 
4 
5 
5 
4 
5 
5 
5 
5 
48 
° QJ 
IV 
0 
0 
1 
0 
0 
1 
0 
0 
0 
0 
2 
d 3 
o 
III 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
-d 
O rj 
<V +2 
II 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
I 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
To ascertain how much influence light had in bringing about this condition, the 
tube with its contents was now placed in perfect darkness and exposed for a moment 
to light every five minutes to record the distribution of the Labidocene. Table 9 
shows the results of this experiment. 
Table 2. 
Here in seven records out of ten all five animals were in the uppermost section; 
in the remaining three records four animals were in the fourth section. Thus the 
record in Table 2, though not quite so nearly uniform as in Table 1, differs so little 
from the latter that the conclusion that female Labidocene stay at the top of the 
water because of some other stimulus than light is entirely justifiable. 
Although, next to light, gravity is the most probable factor in determining the 
distribution of female Labidocerse, it might be assumed from anything that has thus 
far been shown that these animals seek the surface because of the greater abundance 
of oxygen there. To test this assumption a large glass tube, such as that described 
on page 108, was filled with sea water and inverted in an aquarium in such a way that 
no air entered it. Five female Labidocerse were introduced at the lower open end; 
they swam rapidly to the upper end, where they were, of course, at the top of the 
water, but without being in contact with the air. Here they remained till their 
deaths stopped the experiment. The first one died 68 hours after introduction; the 
last one 85 hours. As the animals remained persistently at the upper closed end of 
the tube, it is evident that the atmosphere is not a factor in determining this feature 
of their distribution. If, then, neither light nor atmosphere is essential in keeping 
female Labidocerse at the surface of the water, the only other probable factor is 
gravity, and, as these animals persistently work against gravity in keeping near the 
surface, their geotropism is negative. 
