558 Wisconsin Academy of Sciences, Arts, and Letters. 
meters in August while in June the migrations were one, three, 
and seven meters respectively. With few exceptions, the young 
were nearer the surface in the daytime than the adults and as 
a result their migrations were not so great. In fact, young 
were frequently found at the surface in the daytime in cases 
where the movement of the adults did not exceed a meter or two. 
Burckhardt (4) also found that adult Daphnia hyalina moved 
down about five meters deeper in the daytime than the young. 
In cases where there was a migration of both young and adults, 
the former usually reached the surface earlier in the evening 
and remained later in the morning than the adults. 
Marsh (9b, p. 381) says, “Most of the movement is within 
one meter of the surface, the most marked changes being 
within one-half meter of the surface and below three meters 
the amount of movement is very slight.” In only three of the 
ten lakes were the migrations confined within these narrow 
limits. In the other seven, they varied in extent from two to 
twelve meters and in these cases, of course, the changes extended 
below three meters. The movement of any species, however, 
rarely affected the day vertical distribution in a noticeable 
degree more than three or four meters below the upper limit of 
adults in the daytime. 
The greatest movement shown by any species was the appa¬ 
rent movement of thirty-five meters of Limnocalanus. While 
there is some doubt as to the: exact extent of the movement of this 
form, it could easily make such extensive migrations because it 
is a very good swimmer. Daphnia hyalina showed a, maximum 
movement of seven meters; D. retrocurva, ten meters; D. puli- 
caria, twelve meters; Diaphanosoma brachyurum, five meters; 
Leptodora hyalina, nine meters; Bosmina, four meters; Epis- 
chura lacustris, twelve meters; Diaptomus, five meters; Cy¬ 
clops, ten meters. 
HORIZONTAL MIGRATION. 
In several instances there were evidences of a considerable 
horizontal migration of some of the littoral Crustacea.. Such 
forms as Gammarus, Alona, and Cypris were taken in surface 
catches at night in the limnetic region where the water was 
eighteen meters or more in depth. That is, they were found at 
the regular stations for observations at night but never in the 
