12G 



Ei'ijasllus.— This form was irrogularly distributed in the upper six 

 meters and showed no movement. 



Daphnia liyaUna. — In this species, the young and the adults were 

 counted separately. The ratio between them was very variable. The 

 young constituted from 10 per cent, to 78 per cent, of the 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 

 number of D. hi/alina, were found in the upper seven meters and in this 

 one instance (10 per cent, were in this region. 



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

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

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

 servations, adults appeared at the surface about half an hour after sun- 

 set, and on a fourth occasion about sunset. In tive sets of morning obser- 

 vations, the time of their disappearance from the surface varied from 

 nearly two hours before sunrise as a maximum to thirty minutes before 

 sunrise as a minimum. 



Figs, o and 4 represent both young and adult in the all-night series. 

 It Avill be noted that the curves for young and adult in each series cross 

 and recross each other, showing that the ratio between them was very 

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

 curves for Diaptomus and Cyclops do. In fact, if plotted together, they 

 cross each other several times, one curve showing an increase of indi- 

 viduals at the same hour that the other shows a decrease. In the first 

 series, August 5-(l, the adults reached a pronounced maximum at 8 p. m.. 

 while in the series of August 27-28, two equal maxima were observed, one 

 at 7:30 p. m. and the other at 10 p. m. 



There is the same lack of similarity between the curves representing 

 the young. The first series showed a maximum of young at 8 p. m. and 

 the second at 4:30 a. m. 



Daphnia piilicarla.~lt occupied the region between the middle of the 

 thermocline and the bottom. It was usually most numerous within one 

 to three meters of the bottom. There 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 the only indica- 

 tions of a movement, 



