206 Marsh—Limnetic Crustacea of Green Lake. 
ference in vertical distribution in cold weather as compared 
with that in warm weather I averaged the percentages in the 
upper five divisions from June until September, 1898, —7.96 to 
17.96 inclusive, — and from November to April, 1895,-—24.94 to 
3.95 inclusive,— with the following results: 
0-5 
5-10 
10-15 
15-20 
20-25 
7.96 to 17.96 — warm weather.......... 
70.80 
10.85 
14.50 
2.17 
.48 
24.94 to 3.95 — cold weather........... 
38.47 
14.11 
11.38 
14.51 
10.17 
It is evident from these figures that there is a marked dif¬ 
ference in the vertical distribution in warm and in cold weather. 
Nearly 71 per cent, in warm weather are in the upper five 
meters, while the upper fifteen include 96.15 per cent. In cold 
weather, on the other hand, only 38.47 per cent, are in the upper 
five meters, and below that they are somewhat evenly distributed. 
To determine the difference between day and night I averaged 
the five hauls in October, 1894, which were taken between six 
p. m. and six a m., and compared them with ten hauls taken 
in the same month between six a. m. and six p. m. The fol¬ 
lowing was the result: 
0-5 
5-10 
10-15 
15-20 
Night hauls.... 
24.57 
13.28 
26.84 
19.72 
Day hauls... 
29.27 
19.88 
18.72 
23.58 
It will be seen that the percentages are very similar, and I 
infer that there is no appreciable diurnal migration. I con¬ 
clude from this that they are not very sensitive to changes in 
the amount of light. I take it, too, that while they are affected 
by changes of temperature, they are not very sensitive to such 
changes, or a larger proportion would be found in the warmer 
deep water in the winter. C. fluviatilis, in this respect, differs 
very markedly from Epischura lacustris ) which not only has a more 
pronounced seasonal migration, but moves vertically in accord¬ 
ance with diurnal changes of temperature in the surface water 
