127 



Daphnia rctnjc una. —It w:is rarely fouiul at a gToater depth than 

 seven meters. Both vonny and adult were one to three meters below the 

 surface on clear days. Both appeared at the surface in the evening about 

 half an hour after sunset. In the morning-, however, the adults left the 

 surface ))efore the young. The young usually disappeared about sunrise 

 while the adults moved down from the surface an hour or more before 

 sunrise. The surface maximum of young and adults combined, was found 

 three-quarters of an hour after sunset in the first all-night series and 

 half an hour later in the second, about S p. m. in each case. 



Dkiphanosoiiia hraclii/urinii. — A comparatively small number of this 

 species was found. It was rather irregular in its movements but, in gen- 

 eral, it appeared at the surface thirty to forty-five minutes after sunset 

 and left the surface an hour or more before sunrise. It was found at a 

 depth of one meter, usually, in the daytime, and rarely occurred in catches 

 below a depth of seven meters. 



Ceriodaphniu hiciistris. — This form was confined to the upper four 

 meters and was present in very small numliers. There was no dinrual 

 movement shown by it. 



Leptodorn hi/nJiiat. — Only a small number were found. It occurred in 

 only five of the twenty day series. In these five instances, it was con- 

 fined to the region of the t;iermo( line, that is, between four and eight 

 meters. Both young and adult appeared at the surface in the evening 

 from thirty to forty-five minutes after sunset. The young left the surface 

 about an hour before suiu-ise and the adults half an hour or more earlier. 



Clil/donis and Bosmina wove found in very small numbers. No diurnal 

 movement was noted. 



Ci/pris.—Theve was, apparently, an extended horizontal migration of 

 Cypris as it was found in a third of the morning and evening series, and 

 these observations were made in the deepest part of the lake. In the day- 

 time, however, Cypris was never found in the limnetic region of the lake 

 ))ut in the littoral region. 



A few Corethm larviie were found in and below the thermocline in the 

 daytime. In a few instances they came to the surface at night. 



Not if cm. —The rotifers showed no diurnal movement. With respect 

 to their vertical distrilnition, they form three groups: 



1. M<{Mi(inrriT<i, I'dh/drthra, and AspiaiicJuio were confined to the upper 

 five, six and seven meters respectively, or the region in and above the 

 thermocline. 



