. The crustacea of the plankton, July, 1894-Dec., 1896 . eclines steadily after the lake falls below atemperature of 20°, while Daphnia has its great autumnal pe-riod of reproduction in the month of October when the tempera-ture is below 15°. In the spring of 1897 the warming of thelake was slower than in either of the two years covered by mystudy, and the development of Diaptomus lagged decidedlybehind that of Daphnia. I am not able, however, to give theexact numerical relations. Diagram 9 shows also that Daphnia pulicaria began its courseof development about two weeks in advance of Daphnia h
. The crustacea of the plankton, July, 1894-Dec., 1896 . eclines steadily after the lake falls below atemperature of 20°, while Daphnia has its great autumnal pe-riod of reproduction in the month of October when the tempera-ture is below 15°. In the spring of 1897 the warming of thelake was slower than in either of the two years covered by mystudy, and the development of Diaptomus lagged decidedlybehind that of Daphnia. I am not able, however, to give theexact numerical relations. Diagram 9 shows also that Daphnia pulicaria began its courseof development about two weeks in advance of Daphnia hyalinaAnother fact is disclosed by Figs. 8 and 9, namely, that ineach summer some one species of limnetic crustacean appearsto take the lead, and decidedly dominates the other forms. In 1894, as shown by Fig. 7, this species was Diaptomus. In 1895, as shown by Fig. 8, Daphnia hyalina maintained itsnumbers full through July and August, gradually decliningthrough the autumn, and being nearly twice as numerous as. Trans. Wis. Acad., Vol. XI. Plate Fig. 11.—Crustacea, Sept. 16-30,1894.
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