250 LEE RAYMOND DICE 



PART II. DISCUSSION 

 OBSERVED VERTICAL MOVEMENTS IN DAPHNIA 



Below are given brief statements of some of the recorded 

 observations of vertical movements in Daphnia, with especial 

 reference to Daphnia pulex. 



Juday (1904) found that in Oconomowoc Lake, Wis., in 

 August the adults of Daphnia pulex pulicaria were at a depth 

 of 10 meters in the daytime and reached the surface an hour 

 after sunset. In- doing so they moved up into water that was 

 at least 15° C. warmer than that occupied by them during the 

 day. At this time the young were found at a depth of 6 meters 

 in the daytime, and reached the surface a half hour after sunset. 

 Neither adults nor young were taken in a surface catch made 

 an hour and a half before sunrise. In October, adults were 

 found 13 meters below the surface in the daytime and were 

 taken in a surface catch made two hours after sunset. In 

 June, both adults and young were found at a depth of 1 meter 

 in the daytime. The young reached the surface in the first 

 half hour after sunset and the adults arrived there a half hour 

 later. Both left the surface during the second half hour before 

 sunrise. 



In Okauchee Lake, Wis., in August, "young were found at 

 a depth of 8 meters and adults at 9 meters in the daytime. Two 

 and a quarter hours after sunset young were found at a depth 

 of only 2 meters and adults 4 meters. In October, young were 

 at a depth of 6 and adults 12 meters in the daytime. Three 

 and a quarter hours after sunset the former were at the surface 

 and the latter at 2 meters. In June, the day catches showed 

 young at a depth of 1 meter and adults at 3 meters. The former 

 appeared at the surface about half an hour before sunset and the 

 latter about two hours after sunset. Both disappeared from the 

 surface during the fifth half hour before sunrise." 



Little indication of a diurnal movement by Daphnia pulex 

 pulicaria was found by Juday (1902) in Winona Lake, Indiana. 



In Lake Mendota, Wis., Birge (1895) found no diurnal move- 

 ment in this species during the month of July. During that 

 month the species w T as confined in the vertical space between 

 depths of 6 and 15 meters, and very few were below 12 meters. 

 In this lake the young of the species show a tendency to collect 



