. The crustacea of the plankton, July, 1894-Dec., 1896 . true for those species whosereproductive period comes somewhat late in the spring, and inwhich only the individuals which have lived all winter are pres-ent in the spring. These find the conditions of the open waterof the early spring harder than those under the ice, especiallyas they are exposed to the competition of the increasing swarmsof Cyclops and sometimes of D. pulicaria. The smallest catchesof Diaptomus which are met during the year, are obtained inthe latter part of April when the number of Cyclops has risengreatly—more rapidly
. The crustacea of the plankton, July, 1894-Dec., 1896 . true for those species whosereproductive period comes somewhat late in the spring, and inwhich only the individuals which have lived all winter are pres-ent in the spring. These find the conditions of the open waterof the early spring harder than those under the ice, especiallyas they are exposed to the competition of the increasing swarmsof Cyclops and sometimes of D. pulicaria. The smallest catchesof Diaptomus which are met during the year, are obtained inthe latter part of April when the number of Cyclops has risengreatly—more rapidly than the food has increased. In May there comes a great increase in the number of Diapto-mus. It shows itself first by the presence of a great number ofimmature animals in the upper strata of the water. In bothyears the appearance of these new members of the species wasvery sudden, as will be seen from the following 322 Birge—The Crustacea of the Plankton. Table VII.— Showing the actual number of Diaptomus caught during May. 1895. It will be seen that these catches divide very sharply into twosets, the division coming between the 16th and 18th of May in1895 aod between the 9th and 11th in 1896. Catches earlierthan those given in the table show the same general characteras those given, as also do those taken later. There is no earliercatch which is larger than 1000, nor one later in May smallerthan 2,000 in 1895 or 3,500 in 1896. There is no reason to think that the increase of numbers isdue to small, local aggregations of the species. The increasepersists without intermission for long periods of time duringall conditions of wind and weather. This alone shows that thelarge numbers must occur over great areas of the lake. OnMay 15, 1896, observations were made at different points, andthe numbers were found practically constant at a distance kilometers in various directions from the regular place ofcollecting. It will be seen that the spring increase c
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