DAILY MIGRATIONS OF COPEPODS. 
Ill 
It is evident from this table that the separation of the males from the females 
totally changes the plan of distribution of the males. They become scattered more 
or less uniformly, as in the case of the first class of males. They likewise are undis- 
turbed in their new distribution by the absence of light, as is shown in Table 6, in 
which the distribution of the same five males used for Table 5 is recorded, but with 
the difference that the tube was kept in total darkness except for the brief periods of 
observation. 
Table 6. 
Five-minute 
intervals. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
Totals. 
v 
0 
i 
1 
2 
1 
1 
0 
i 
i 
1 
9 
° oi 
IV 
1 
0 
1 
1 
1 
1 
9 
i 
i 
2 
11 
O 4- • 
4-S <D 
O c* 
III 
II 
I 
1 
2 
1 
2 
0 
2 
1 
1 
1 
0 
1 
1 
1 
1 
1 
0 
l 
1 
l 
0 
1 
2 
0 
1 
0 
1 
1 
10 
9 
11 
The essential agreement of Table 5 with Table 3 and of Table 6 with Table 1 
shows that all males react or fail to react to light, gravity, etc., in much the same way, 
and that it is the responses to the females rather than to other factors that divide the 
males into two classes. So far as their reactions to light, gravity, etc., are concerned, 
all males form in reality only a single class. 
It must be evident from the preceding experiments that light is a very subor- 
dinate factor in determining the distribution of the males, if, in truth, it is to be 
reckoned with at all, and it might further be supposed, since the males when left to 
themselves do not collect either at the top or at the bottom of the aquarium, that 
they therefore are also uninfluenced by gravity, i. e., that they are not geotropic. 
This conclusion, however, would be erroneous, in my opinion, for the bodies of the 
males are quite as heavy as those of the females, and are continually falling toward 
the bottom. If the males did not react against this, i. e., were slightly negatively 
geotropic, they would eventually all reach the bottom, a form of distribution which 
we know does not occur. 1 therefore believe that the males also are negatively 
geotropic, but only sufficiently so to keep them from collecting at the bottom and 
not enough to cause them to collect at the top, as the females do. 
Two conclusions may now be regarded as well established: first, that the female 
Labidocerse are strongly negatively geotropic, and, secondly, that the males are 
slightly so. The first of these makes clear why under natural conditions the females 
come to the surface of the sea and stay there; neither helps us to understand why 
the males congregate with the females or why the latter at stated intervals desert 
the surface of the sea. 
Loeb (1893) long ago pointed out that by appropriate stimulation the sense of 
an animal’s response might be inverted; thus an organism positively phototropic 
under ordinary conditions might by a slight change in its environment become 
negatively phototropic. It is therefore necessary, in attempting a further insight 
into the daily migrations of the copepods, to ascertain whether there are not means 
at hand for converting the negative geotropism of the females into a positive geo- 
tropism, thus establishing a sequence of events that might offer an explanation of 
daily migration. Heretofore some of the most successful means in accomplishing 
such inversions have been mechanical stimulation, as agitation of the water in which 
the animals are, and changes in the density and in the temperature of the sea water. 
