480 Birge—Vertical Distribution of Pelagic Crustacea. 
nearly one-half of the Crustacea in the upper 3 m. during the 
summer, and observations continued into the early fall show the 
same result. It is not necessary to count the Crustacea in order 
to see the difference in number from different levels. The six 
bottles of a series can be placed in order with certainty, except in 
those cases where the bottom level and that next above it con¬ 
tain almost nothing. The total amount varied, but that from 
the upper level was always the largest. 
As confirming the accuracy and sufficiency of the method em¬ 
ployed, we may briefly refer to results obtained later in the 
>ear—in October. As soon as the temperature of the lake be¬ 
came uniform from top to bottom the Crustacea became pretty 
uniformly distributed, showing an arrangement wholly different 
from that of the summer months. One example is added: 
Number of Crustacea caught. 
Oct. 17, 9 A. M. 
Diaptomus. 
Cyclops 
D. hyalina. 
Temp. 
Meters. 
0-3. 
192 
732 
702 
0.10 m 
12.850 C 
3-6. 
234 
666 
678 
6-9... 
186 
1098 
576 
9—12.. 
282 
978 
300 
12-15. 
228 
720 
480 
15—18...... 
164 
696 
564 
18 m 
13.10° O 
Total. 
1364 
4890 
3280 | 
Other catches were about the same in proportion, though dif¬ 
fering in numbers, as would be expected. This disclosure of the 
change in distribution, which came on rather gradually during 
some two weeks, together with the concordance in the result of 
observations taken about the same time, seems to give addi¬ 
tional confidence in the results obtained by our methods. 
A second peculiar fact of distribution, also of uniform occur¬ 
rence, is the singular vertical position of Daphniapulicaria dur¬ 
ing July. If little confidence could be placed in our methods,, 
this curious result could hardly have been reached. D. pulicaria 
did not differ widely in number from D. hyalina , yet the distri¬ 
bution of the two species was as distinct as possible. An un- 
