ANNUAL DISTRIBUTION OF THE ORGANISMS. 25 



of about eighty feet, while the maximum depth of Lake Win- 

 nebago is only about twenty-five feet, and because of its greater 

 extent is doubtless much more affected by the winds. It seems 

 to me that if the species were especially sensitive to tempera- 

 ture we should expect the fall maximum in the deeper lake 

 rather than in the shallower, as seems to be the case. 



Epischura lacustris Forbes. 



Epischura is distinctly a summer form. As shown in the 

 curves (Plates IV and V) it appears sometimes as early as 

 May and may be found as late as December or even January. 

 In Green lake the larval forms appear in February and March. 

 This is not indicated on the curves of the Epischura plate, as in 

 the counting the Epischura larvae were not distinguished from 

 those of the other copepods. The period of maximum devel- 

 opment occurs in July or August. It will be noticed that the 

 spring increase occurs a little later in Green lake than in Lake 

 Winnebago, and that the summer maxim am of Green lake is 

 also a little later than that of Lake Winnebago. Epischura 

 remains in Green lake, too, later into the fall than it does in 

 Lake Winnebago. This is without doubt due to the fact that 

 Green lake warms up so much more slowly, and cools off in the 

 fall with corresponding slowness. 



The curves conform quite closely with the results given in 

 my '97 paper, except that in the winter of '95 there was a large 

 rise in March. This difference is accounted for by the fact 

 that in the '95 collections a distinction was made between the 

 Epischura larvae and the other copepod larvae. 



The annual occurrence of Epischura in Lake Winnebago re- 

 sembles very closely the results given by Birge for lake Men- 

 dot a. , 



The. nearest European relative of Epischura,, Heterocope, is 

 stated by Apstein to occur from July to November, with a max- 

 imum in the summer, thus showing a resemblance in its period- 

 icity to Epischura. 



