12G 



Er</a><iltts. — This form \v;is in'r,i;iilarl.v distributed in tlic upyer six 

 meters and showed no movement. 



Daphnia liyaUna. — In tliis si)ecies, the yoimg and tlie adults were 

 counted separately. The ratio l)etween them was vei'v varialde. Tlie 

 young constituted frtnn 10 per cent, to 78 per cent, of tlie entire number 

 of individuals of a series. The young predominated near the surface on 

 bright sunny days and the adults predominated in the deeper strata.. In 

 all but one set of observations. 70 per cent, to 95 per cent, of the total 

 nunibci- (if />. lii/dliiia. were found in the uiiper seven meters and in this 

 one instance (iO per cent, were in tliis region. 



Usually a few young were found at the surface in tlie daytime. Lilvc- 

 wise adults were found at the surface on two cloudy days Imt, on clear 

 days, they were at a depili of one to two meters. In tliree sets of ob- 

 servations, adidts appeared at the surface aliout half an hour after sun- 

 set, and on a fourth occasion about sunset. In Hve sets of morning ol)ser- 

 \atioiis, Ihe tinu' of tlieir disappearance from the surface varied from 

 nearly Iwd lionrs before sunrise as a maximum to tliirly minutes Itcfore 

 sunrise as a minimum. 



I-'igs. :! and \ r(>present Iiolli young and adult in (lie all niglit sei'ics. 

 It will be noted that tlic curves for young and adull in each series cross 

 and recross each other, sho\\iiig thai the ratio between them was vei'y 

 variable. The two curves for adults do not show the similarity that tlie 

 curves foi- ]>iaptomus .iiid Cydoiis do. In fact, if plotted together, they 

 cross each other se\eral times, one cur\'e showing an increase of iudi- 

 ^■iduals at the same hour that tli(> otliei- shows a decrease. In the lii'st 

 series, .\ugust .'i-O. the adults readied a iironoimced maximum at S ji. in., 

 while in the series of August •_'7-'JS. two e(iii,il maxima were observed, one 

 at 7:."'.o p. m. and the otlier ;it lo ]). ni. 



There is the same la<-k of similarity between tlie curves repi'eseiiting 

 the young. The tirst series showed a iiiaximum of young at S p. in. ami 

 tile second at 4:.".0 a. m. 



IhijiJiiiid imliciniii. — It occuiiied tlie region lietween the middle of the 

 thermocliue and tlie bottom. It was usually most numerous within one 

 to three meters of the bottom. Ther(> was practically no diurnal move- 

 ment. Adults were found at the surface in one evening catch and at a 

 depth of only one meter in a night catch. These were th(> only indica- 

 tions of a movement, 



