. The crustacea of the plankton, July, 1894-Dec., 1896 . Numbers enclosed in a parenthesis rest on observations madeon a single day. The females which have lived over winter produce at leastthree broods of young, and die in June, chiefly in the early partof the month. Those individuals which have lived over winterare readily distinguished from those hatched in the spring bythe smaller size and different shape of the head. It is easy,therefore, to determine the average length of their life at aboutsix to eight months, from early October to early June, as amaximum. It is not possible to g
. The crustacea of the plankton, July, 1894-Dec., 1896 . Numbers enclosed in a parenthesis rest on observations madeon a single day. The females which have lived over winter produce at leastthree broods of young, and die in June, chiefly in the early partof the month. Those individuals which have lived over winterare readily distinguished from those hatched in the spring bythe smaller size and different shape of the head. It is easy,therefore, to determine the average length of their life at aboutsix to eight months, from early October to early June, as amaximum. It is not possible to get similar data for the sum-mer form of this species, for the shape of the head-crest alters in all individuals as the water cools in the autumn. The swarms of young produced in October rapidly diminishin number at first, but an equilibrium is reached by the first ofJanuary, and thenceforward the decline through the winter isvery slow, or imperceptible. The statements made regardingDiaptomus fully apply to this species also. During April and. 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 thistime. The rise in number in the spring comes on very species apparently reproduces first in the warmer andshoaler waters at the edge of the lake, and the individuals thusproduced are distributed over the surface of the lake by favor-able winds. This supposition is necessary in order to accountfor the extraordinarily rapid increase in numbers which the spe-cies shows. The following table gives the actual number caughtin 1895 and 1896 on the dates stated: Table XVI.— Actual number of specimens caught. 1895. April 25April 30May 20.,May 27. 144510442 1,0003803,0601,2104,8204,510 1896. April 22April 27April 30May 11 .May 15 .May 20May 26. 3801201401,3601,1401,6001,6205,6604,9005,460 It will be seen that the number o
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