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. 



April 25 

 April 30 

 May 7.. 

 May 12. 

 May 16. 

 May 18. 

 May 20.. 

 May 22. 

 May 27. 



144 

 510 

 442 



1,000 

 380 

 3,060 

 1,210 

 4,820 

 4,510 



1896. 



April 22 

 April 27 

 April 30 

 May 2.. 

 May 4. . 

 May 8.. 

 May 11 . 

 May 15 . 

 May 20 

 May 26. 



380 

 120 

 140 

 1,360 

 1,140 

 1,600 

 1,620 

 5,660 

 4,900 

 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 fres hly 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 



