416 
Birge—The Crustacea of the Plankton. 
In 1897 similar observations were made by the aid of the 
pump; 40 liters of water being ordinarily pumped from 
each level. The results were substantially the same, al¬ 
though the number of Crustacea found in and above the thermo- 
cline was smaller, since the population of the lake was smaller 
in 1897 than in the preceding year. The following table shows 
the results of some of the observations. It will be noticed that 
the abruptness with which the Crustacea stop is evidence that 
the pump did not draw water from any considerable distance 
from the mouth of the suction hose. 
Table XXXIX.— Typical catches from the thermocline stated in thousands per 
cubic meter. See also Table XXXVIII. 
Depth, meters. 
Temperature. 
Diaptomus. 
Cyclops. 
.2 
>> 
rd 
ft 
D. retrocurva. 
cS 
«s 
o 
'B 
a 
A 
Diaphanosoma. 
Ergasilus. 
o 
+3 
ft 
ffi 
A 
Total crustacia. 
Nauplii. 
Corethra. 1 
t 1 
9 
21.6° 
8.7 
7.6 
6.8 
0.2 
4.8 
0.8 
0.05 
50.5 
4.1 
0.05 
10 
21.5 
6.0 
8.8 
8.7 
1.5 
5.3 
1.3 
0.05 
53.1 
3.2 
11 
17.5 
4.8 
1.8 
0.5 
0.3 
0.02 
24.7 
11.8 
0.1 
12 
15.9 
4.0 
8.7 
28.6 
5.8 
0.15 
13 
15.1 
0.2 
11 
20.6 
1.0 
5.0 
5.0 
4.3 
15.3 
9.2 
12 
19.0 
1.0 
5.0 
2.8 
1.5 
1.8 
12.1 
10.0 
13 
15.0 
0.1 
0.1 
0.08 
11 
21.3 
10.2 
8.4 
3.0 
3.0 
24.6 
11.4 
12 
21.2 
7.8 
13.8 
7.2 
0.6 
3.9 
23.3 
11.1 
12.5 
20.4 
2.4 
29.3 
1.6 
1.2 
34.5 
16.5 
13 
16.2 
0.1 
0.1 
0.2 
0.05 
14 
15.0 
0.05 
0.05 
0.05 
0.15 
0.05 
10 
20.5 
1.4 
7.8 
5.0 
2.5 
16.7 
19.5 
11 
20.4 
2.5 
9.2 
8.2 
2.5 
22.4 
42.5 
0.05 
12 
17.6 
1.3 
13.2 
1.0 
10.0 
25.5 
34.4 
0.15 
13 
15.6 
0.05 
0.1 
0.02 
0.17 
0.15 
14 
15 
15.0 
13.0 
0.05 
0.1 
0.1 
0.25 
0.2 
A. 
Aug. 17. Sur¬ 
face tempera¬ 
ture, 21.8°. 
b. ; 
Aug. 25. Sur-J 
face tempera-j 
ture, 22.7°. I 
C. 
Aug. 27. Sur¬ 
face tempera--* 
ture 21.5°. 
D. 
Aug. 28. Sur¬ 
face tempera¬ 
ture 21.2°. 
