Juday—Diurnal Movement of Plankton Crustacea. 559 
daytime. The horizontal migration of Cypris was also noted 
by the author in Winona lake (8b, p. 127). 
TIME OF MAXIMUM NUMBER AT THE SURFACE. 
Blanc (3) found the Crustacea most abundant at the surface 
at 4 a. m. in lac Leman. Fordyce (6) obtained the same result 
for Leydigia fimbriata. Fuhrman (7) states that in his obser¬ 
vations the Crustacea reached 1 a maximum at the surface shortly 
before sunrise. As none of my observations extended through 
the entire night, it is impossible to say at what time the maxi¬ 
mum number was present at the surface. However, some of 
the morning observations were made early enough to show that 
the maximum period was not as late as 4 a. m., especially dur¬ 
ing the months of June;, July, and August. In many instances, 
the D'aphnias, Leptodora and Epischura disappeared entirely 
from the surface before this hour and when they were present 
so late as this, they were found to be fewer in number than an 
hour or two earlier. In general, the Crustacea were not so abun¬ 
dant in the morning catches, and some of them were made as 
early as 2 a. m., as in the evening catches, especially those made 
from one to two hours after sunset. These facts go to show 
that the maximum period probably came in the early part of the 
night rather than toward morning. Such a condition would be 
in harmony with the results obtained for Winona lake (8b, 
p. 128) where most of the Crustacea were found in greatest 
abundance at the surface from 7:30 to 8 p. mi. in August. 
ORDER OF REACHING THE SURFACE AND LEAVING IT. 
The order in which the Crustacea appeared at the surface in 
the evening varied somewhat but in general the Copepoda pre¬ 
ceded the Cladocera. This agrees with Blanc’s (3) observa¬ 
tions. Cyclops seemed to be affected least by the factors that 
are responsible for this movement. It was found in all ten of 
the lakes but there were daily migrations in only four. Even¬ 
ing catches in two of these four lakes, however, show that Cy¬ 
clops ranked about the same as Daphnia hyalina in the order of 
reaching the surface. The following three are named in the 
order of their appearance, Diaptomus, Daphnia hyalina>, and 
D. pulicaria. Diaphanosoma ranked about the same as Diap - 
