The Annual Distribution of the Crustacea. 31S 
ing the same months, those individuals of Daphnia retrocurva 
disappear, which have survived the reproductive period. Diap- 
tomus begins its decline in September or early October, and 
seems to make no special provision for winter forms. Cyclops 
continues its reproductive activity through the year, at least in 
periods when the temperature of the lake is above 2° C., but 
with a rate of multiplication declining as the temperature falls 
below 15°. Larval Copepods are present in great numbers at 
all seasons, but their development into later stages is checked in 
winter. Chydorus seems to have the same habit as Cyclops; but r 
for causes as yet unknown, it almost disappeared in the winters 
of 1894-5, 1896-7, although abundant in the preceding autumns,, 
and present in considerable numbers in the winter of 1895-6. 
Daphnia pulicaria had a marked reproductive period in early 
December, and continued reproduction at a slower rate through¬ 
out the winter. Diaplianosoma disappears in October, and 
Leptodora in late November or early December. 
Table IV. — Average number of Crustacea for each two-week period and 
their sum , stated in thousands and tenths per sq. meter of surface. 
Diap- 
tomus. 
clops. 
D. puli¬ 
caria. 
D. hya- 
lina. 
D. 
retro¬ 
curva. 
Chy¬ 
dorus. 
Diap- 
hano- 
soma. 
Total. 
1894. 
July 1-15. 
242.2 
39.8 
6.4 
19.8 
a 
a 
a 
306.2 
July 16-31. 
398.9 
151.0 
8.3 
13.3 
a 
a 
0.8 
472.3 
August 1-15. 
218.7 
161.0 
1.1 
16.6 
a 
a 
6.3 
401.1 
August 16-31. 
September 1-15. 
87.4 
200.3 
0.8 
60.7 
a 
15.0 
18.0 
382.2 
September 16-30. 
54.6 
190.1 
a 
148.4 
a 
378.9 
19.6 
691.6 
October 1-15.. 
67.6 
347.1 
a 
207.6 
a 
193.3 
5.2 
830.8 
October 16-31. 
38.3 
261.3 
a 
353.5 
a 
202.0 
3.0 
757.1 
November 1-15. 
44.0 
246.4 
a 
183.1 
a 
97.9 
a 
571.4 
November 16-30. 
December 1-15. 
23.9 
75.0 
a 
121.5 
a 
9.5 
a 
219.9 
December 16-31. 
(16.7; 
(44.5) 
a 
(49.0) 
a 
(1.65) 
a 
(111.9) 
1895. 
January 1-15. 
17.5 
Z1.5 
a 
40.8 
a 
1.3 
a 
81.1 
January 1-15. 
(15.9) 
(40.0) 
a 
(55.9) 
a 
(2.0 ) 
a 
(111.8) 
February 1-14. 
(44.5) 
(80.8) 
a 
(75.3) 
a 
a 
a 
(200.6) 
