Daphnia hyalina. 
337 
and the early part of May, the species declines on the whole, 
and the smallest catches of the year have been made at this 
time. The rise in number in the spring comes on very rapidly. 
The species apparently reproduces first in the warmer and 
shoaler waters at the edge of the lake, and the individuals thus 
produced are distributed over the surface of the lake by favor¬ 
able winds. This supposition is necessary in order to account 
for the extraordinarily rapid increase in numbers which the spe¬ 
cies shows. The following table gives the actual number caught 
in 1895 and 1896 on the dates stated: 
Table XVI .—D. hyalina. Actual number of specimens caught. 
1895. 
1896. 
April 25... 
144 
April 22... 
380 
April 30... 
510 
April 27..... 
120 
May 7. 
442 
April 30.. 
140 
May 12. 
1,000 
May 2... 
1,360 
May 16. 
380 
May 4. 
1,140 
May 18. 
3,060 
Mav 8. 
1,600 
May 20.. 
1,210 
May 11. 
1,620 
May 22.. 
4,820 
May 15. 
5,660 
May 27. 
4,510 
May 20 .. 
4,900 
May 26. 
5,460 
It will be seen that the number of the species increased 
nearly tenfold in two days, and that this sudden increase was 
held with fair uniformity, so that, while all the catches up to 
May 16, 1895, and April 30, 1896, were small, all those made 
after those dates were large. 
In 1895, the appearance of the eggs was carefully studied. 
On April 15th, when the surface temperature was 4.5° C., 
all of the specimens seemed to have freshly molted, and one con¬ 
tained eggs. Three days later more than a third of the speci¬ 
mens contained eggs, which were mostly young. On the 25th 
all had eggs, many of which were half developed. On May 4th, 
young were found. On May 12th, a very few young were seen, 
including one male, but many had no doubt been hatched at this 
time, as on the 18th the numerous young were developing ovaries, 
22 
