194 Marsh—Limnetic Crustacea of Green Lake. 
did not find some representatives of this genus in every five 
meter stratum, and yet from sixty to seventy-five per cent, 
were commonly in the upper ten meters. 
In order to find out whether there was any difference in the 
vertical distribution in summer and in winter I took the 
averages in the upper three levels of collections 7.96 to 17.96 
inclusive, and 24.94 to 3.95 inclusive. I took these years 
because in 1894-5 I made a large number of collections in cold 
weather, and in 1896 I made the largest number of collections 
in warm weather. 
The following table indicates the results: 
0-5 
5-10 
10-15 
Summer, 7.96-17.96.... 
49.31 
24.49 
12.26 
Winter, 24.94-3.95... 
50.02 
13.50 
10.12 
It appears from these averages that the seasons make no 
difference in the vertical distribution of Diaptomus , but that it 
is uniform throughout the year. 
Apstein comes to the same conclusion. (’96, p. 180.) 
The day and night collections of October, 1894, compared as 
follows: 
0-5 
5-10 
Day..... 
59.44 
18.42 
Night ..... 
53.70 
18.40 
Here is no evidence of diurnal migration. 
I think, then, that I am safe in saying that the vertical dis¬ 
tribution of Diaptomus varies but little from one end of the 
year to the other and is not appreciably affected by changes in 
the amount of light. 
Birge finds the same thing to be true of D. oregonensis. 
(Birge, ’95, 450.) 
