J uday—Diurnal Movement of Plankton Crustacea. 547 
face during the first half hour after sunset and left again dur¬ 
ing the second half hour before sunrise. 
Leptodora hyalina .—This species was at a depth of six 
meters in the day catches. It came to the surface during the 
first half hour after sunset but left the surface earlier than one 
and a half hours before sunrise. 
Bosmma .—This form was at a depth of one meter in the day 
series but came to the surface shortly before sunset. It was 
not present in the surface catch made as early as one and a half 
hours before sunrise. 
Epischura lacustris .-—This species was not found above a 
depth of twelve meters in the day catches. It reached the sur¬ 
face during the first half hour after sunset and left again earlier 
than an hour and a, half before sunrise. 
Limnocalanus macrurus .—Only one individual of this form 
was found above a depth of fifty meters in the day catches. In 
the night series, ten were present in the catch made at fifteen 
meters and others were found in the catches made between fif¬ 
teen and fifty meters. No individuals were found in any of 
the night catches made above the thermocline, that is, above 
fifteen meters. 
Diaptomus .—The young of this form were found at the sur¬ 
face in the daytime and adults at a depth of four meters. The 
latter appeared at the surface shortly before sunset and disap¬ 
peared during the first half hour after sunrise. 
Cyclops .—Young were at a depth of two meters and adults 
eight- meters in the day series. The former reached the surface 
shortly before sunset and the latter during the third half hour 
after sunset. Both left the surface about sunrise. 
Nauplii .—There was no diurnal movement of the nauplii. 
Marsh also (9a, p. 217) noted diurnal migrations of Daphnia 
retrocurva, Diaphanosoma, Diaptomus, Epischura, and Lim~ 
nocalanus in Green lake. 
LAKE MENDOTA. 
The observations on lake Mendota were made during the 
month of October, 1900 and between April 24 and June 27, 
1901. Over three hundred catches were made during these two 
periods. 
Daphnia hyalina .—In October, young were found at the sur¬ 
face in the daytime except for a brief period in the middle of 
