Vertical Distribution of Individual Species. 
393 
Table XXXII — Percentile distribution. Summer — Diaptomus. 
Average 
No. 
Per cent, in each 3 m. level. 
0-3 m. 
3-6 
6-9 
9-13 
13-15 
15-18 
1894. 
226,000 
49.2 
29.3 
16.6 
4.1 
0.5 
0.3 
1895. 
172,000 
42.7 
29.0 
20.9 
6.1 
0.7 
C.6 
1896.... 
188,000 
52.6 
27 4 
12.4 
5.9 
1.9 
0.5 
Cyclops. 
1894. 
138,000 
40.7 
28.4 
20.1 
9.4 
1.7 
0.3 
1895 . 
183,000 
39.3 
25.2 
19.0 
10.0 
3.1 
3.4 
1896 . 
290,000 
40.2 
27.1 
15.6 
10.1 
4.8 
2.3 
Daphnia hyalina. 
1894 . 
27,000 
41.9 
23.8 
21.4 
6.7 
1.0 
r 
0.3 
1895 ... 
210,000 
52.3 
20.8 
17.6 
6.6 
1.3 
1.2 
1896 . 
145,000 
44.7 
22.2 
16.1 
11.7 
4.7 
1.3 
The variations in the distribution of Diaptomus are greater, 
although its numbers were more nearly constant, but in each 
year the same characteristics are shown. The percentage of the 
population found below the middle of the lake is 7.5 or less, 
while in the case of Cyclops the number ranges from 11.5 to 
more than 17 per cent. Daphnia hyalina also varies more in 
the upper strata, but is in general intermediate in its distribu¬ 
tion between the other two genera. The older individuals of 
Daphnia hyalina are much more apt to accumulate in the lower 
part of the water accessible to them than is the case with Diap- 
tomus , and consequently the lower levels are apt to contain a. 
larger percentage of this species. On the other hand the spe¬ 
cies does not extend to the thermocline in numbers anything 
like as great proportionately as does Cyclops , so that the lower 
part of the inhabited water always contains a larger proportion 
of Cyclops than of any other species. 
The vertical distribution of Daphnia hyalina , therefore, dif¬ 
fers very considerably in different years. If the species is pres¬ 
ent in large numbers and the young are constantly appearing, a 
