554 Wisconsin Academy of Sciences, Arts, and Letters. 
C eriodaphnia. 
This form was found in five lakes but no diurnal movement 
was noted in any of them. 
Diaphanosoma brachyurum Lievin. 
This speeies was present in nine lakes. There was a move¬ 
ment in five of these which varied in extent front one meter to 
five meters. In three lakes, adults appeared at the surface dur¬ 
ing the first half hour after sunset and in another, during the 
fourth half hour after sunset. In two lakes, they left the sur¬ 
face more than an hour and a half before sunrise, while in two 
others they left during the second half hour before sunrise. 
Morning and evening observations were not made in the fifth 
lake. 
Leptodora hyalina Lilljeborg. 
Leptodora was obtained in eight of the ten lakes and a defi¬ 
nite movement was noted in five of them. In the other three 
lakes so few individuals were found that it was impossible to 
determine with certainty that there was a movement, although 
there doubtless was. In four lakes, there was a diurnal migra-r 
tion of five to nine meters. It was not taken in the day catches 
of the fifth lake. For this species, also, this movement is much 
smaller than was found by Burckhardt (4), twenty meters. 
There was considerable irregularity in the movement of this 
form and this* agrees with Burckhardt’s observations. 
Concerning the time of arrival at and departure from the 
surface, Marsh (9b) states that Leptodora appears at the sur¬ 
face “at almost exactly forty-five minutes after sunset, remains 
at the surface during the night, and disappears again at just 
three-quarters of an hour before sunrise.” My observations 
did not yield such definite results. Taking all five of the lakes 
into account, the time of arrival at the surface varied between 
the limits of less than half an hour after sunset and almost two 
hours after sunset. In observations on Lake Mendota, adults 
reached the surface during the first half hour after sunset on 
June 3, 1901, and not till the third half hour after sunset on 
June 24, while the young showed even a greater range of varia¬ 
tion. Both young and adults showed almost, if not quite as 
