Cyclops. 



327 



Table X. — Winter number of Cyclops, stated in thousands per sq. m. 



November 1-15.. 

 November 16-30. 

 December 1-15 . . 

 December 16-31. 



January 1-15 



January 16-31 . . . 

 February 1-14 . . 

 February 15-28 . 

 March 1-15 



March 16-31. 

 April 1-15... 

 April 16-30.. 



1894-95. 



246.4 



75.0 

 (44.5) 



21.5 

 (40.0) 

 (80.8) 



73.1 



55.7 



66.2 



53.9 



242.5 



1895-96. 



144.7 



135.4 



90.2 



89.1 



111.0 



151.0 



91.6 



82.0 



old. yg. 

 51.2 161.3 



400.7 



1011.2 



1896. 



267.7 



173.9 



115.5 



93.1 



It will be seen that the winter numbers are more variable 

 during the season than are those of Diaptomus. This results 

 from two causes; first, the fact that reproduction continues 

 longer in the autumn than in Diaptomus and therefore the spe- 

 cies reaches its winter minimum at a later date; second, re- 

 production may begin again during the winter and cause a con- 

 siderable increase before the opening of the lake in the spring. 

 A third fact ought to be added. During the winter there are 

 often caught large numbers of Cyclops in the deeper water, 

 where there are plainly aggregations of the species. Such 

 catches of course raise the average for the two-week period in 

 which they happen to come. 



The spring rise comes on immediately after the opening of 

 the lake or, as already said, begins while the lake is still covered 

 with ice. The increase is rapid but by no means so sudden as 

 is the case in Diaptomus. This may be seen from the following 

 table of catches, in which by no means all the observations of 

 the periods are given. 



