Juday—Diurnal Movement of Plankton Crustacea. 541 
Ceriodaphnia .—This form was rare and did not show diurnal 
movement. 
Diaphanosoma brachyurum .—This species did not show di¬ 
urnal movement in August and only a slight change in October. 
It was not found in June. 
Leptodora hyalina .—In August, young were found at the 
surface in the daytime 1 and adults at a depth of nine meters. 
The latter appeared at the surface during the second half hour 
after sunset and left the surface during the second half hour 
before sunrise. Ho definite movement was observed in Octo¬ 
ber. 
Both young and adults were found at a depth of seven meters 
in the daytime in June. The former appeared at the surface 
during the first half hour after sunset and adults about an hour 
later. Bloth left the surface during the third half hour before 
sunrise. 
Bosmina.—Bosmina was at a depth of one meter in the day- 
timje in August. It appeared at the surface during the second 
half hour after sunset but did not leave the surface until after 
sunrise. Ho diurnal movement was observed in October and 
J une. 
Cliydorus .—This form was not found in August. It was 
rare in October and common in June but it did not show diur¬ 
nal movement on either occasion. 
Epischura lacustris .—This species was not found in any of 
the day catches! in August. It appeared at the surface, how¬ 
ever, during the second half hour after sunset and disappeared 
again during the second half hour before sunrise. It was not 
found in October. In June, it was not. present, in any of the 
day catches but it appeared at the surface during the 1 second half 
hour after sunset and disappeared during the second half hour 
before sunrise. 
Diaptomus, Cyclops, and nauplii did not show diurnal move¬ 
ment. 
Corethra larvae.—Larval Corethra showed no diurnal move¬ 
ment in August. It was not found above a depth of twenty 
meters in any of the day catches in October but it was found at 
a depth of only one meter at night. Only one individual was 
observed in all the catches made in June. 
