808 The American Naturalist. 



[September, 



thus far are interesting, and I think later collections are not likely to 

 modify, to any great extent, the conclusions I have formed. 



The results were a little disappointing to me at first, I must confess. 

 I had made up my mind that I should find the three regions character- 

 istic of the deep sea — the pelagic, intermediate and abyssal. It was 

 rather discouraging, then, when I found material in my dredge from 

 all depths. Not only that, but when I began to examine the collec- 

 tions under the microscope, I found certain species, which I had con- 

 sidered peculiar to the surface — like Diaptomus minutus — occurring all 

 the way from the surface to the mud of the bottom. The barren inter- 

 mediate zone, then, does not exist in Green Lake. It is true, however, 

 that the numbers of individuals are less at intermediate depths than 

 near the surface or near the bottom, and that some species are vastly 

 more numerous in the upper zone, while others are almost entirely con- 

 fined to the lower. 



I counted the number of individuals in each haul, and after reduc- 

 ing the numbers to percentages, tabulated the results. 



I will give brielly the conclusions I reached in regard to those spe- 

 cies which are found most commonly. 



The species which is found in the greatest numbers is Diaptomus 

 minutus. In one haul this was associated with D. sicilis (a somewhat 

 rare form in Green Lake), and in my computation I did not separate 

 the two, as their habits are identical. On the average, 46 per cent of 

 this species is within five meters of the surface, and 59.4 per cent within 

 ten meters. Within ten meters of the bottom are only 7.37 per cent. 

 It is evident that more than one-half of the individuals of these species 

 are found within ten meters of the surface, and that from that point to 

 the bottom, the numbers steadily decrease. 



Daphnella is more exclusively pelagic — 79 per cent being found 

 within ten meters of the surface, and only 5.6 per cent at the bottom. 



Episehura is still more distinctly pelagic — 81 per cent being in the 

 first ten meters, and 3.3 per cent in the last ten. 



Leptodora, Bosmina and Cyclops fluviatilis are also found much more 

 abundantly near the surface. Leptodora rarely goes below fifteen 

 meters. 



Daphnia kahlbergiensis seems somewhat erratic in its distribution. 

 On the average, nearly 43 per cent are found within the first ten 

 meters, but nearly 25 per cent are found in the last ten. Generally 

 speaking, they appear more numerous near the surface and the bottom, 

 but less so at intermediate depths. But they may occur at all depths, 

 and sometimes quite numerously in the intermediate region. 



