DAILY MIGRATIONS OF CO PE PODS. 
115 
Table 7. 
Number of experiment. 
1 
2 
3 
4 
5 
6 
7 
8 
0 
10 
Totals. 
Number of animals in chamber to- 
ward light 
5 
4 
4 
6 
4 
3 
6 
4 
5 
5 
46 
Number of animals in chamber away 
from light 
5 
6 
6 
4 
6 
7 
4 
6 
5 
5 
54 
These results support in the main the opinion formed from the more cursory 
inspection of the jar. As a whole the assemblage of males shows slightly negative 
phototropism. These experiments do not, however, preclude the possibility that 
some individuals are slightly positive and some indifferent; they merely show that 
more individuals are slightly negative than otherwise. When a single male is put in 
a large open glass jar, the animal can usually be driven about from one side to the 
other by holding an electric light (14-candle power) close to the jar. The reaction is 
never very quickly performed and sometimes fails entirely, but usually after a few 
minutes the animal swims from the illuminated side to the opposite one and stays 
there persistently. Although it is generally not difficult to drive a male Labidocera 
by light back and forth horizontally through a jar, I found it almost impossible to 
drive them up or down through a thickness of water equal to that through which 
they" would move horizontally. Sometimes this seemed to succeed, but generally not, 
and I was finally forced to conclude that, slight as the geotropisnr of the males was, it 
was more effective than their phototropism. 
Female Labidocerte collect on the light side of a jar with great precision. Since 
they are also negatively geotropic they keep close to the top of the water. When ten 
females were exposed to light in the square glass jar with the partition as described 
for the males (p. 114), all were found in all ten trials in the chamber next the light. 
Their positive phototropism is thus clearly indicated. 
Further evidence of this peculiarity was observed in several ways. The large 
upright glass tube marked off at 10-centimeter intervals (p. 108) was tilled with sea 
water to the 50-centimeter level and five females were placed in it. The whole was 
exposed to diffuse daylight in a room, and the Labidocerte soon congregated at the 
top of the water on the side of the glass nearest the window. An opaque cover was 
now slipped over the top of the tube and down to the 40-centimeter mark. In a few 
moments all five animals had dropped to this level, and remained here as long as the 
cover was kept in this position. This result was essentially the same as that observed 
by Loeb (1893, p. 160) for Temora longicornis , except that in Loeb’s experiments the 
copepods were checked in their upward movements by the opaque cover instead of 
being driven downward by it. In either case it shows that the animal’s positive 
response to light is stronger than its negative response to gravity. By lowering 
such an opaque hood over the tube the Labidocerte were driven to the bottom of the 
tube, where they remained as though imprisoned. They retained this position as 
long as a small amount of light was allowed to enter at the bottom, but the moment 
this was cut off they presumably began to rise, for on removing the hood ten minutes 
later they were all found at the top of the water. Thus their negative geotropism 
is at once made effective by complete darkness. 
