133 
at temperatures rarely below 70°. The earliest record in channel 
waters was on May 1, 1896, at 68.75°, and the latest on November 
15, 1897, at 47°. Of the 28 records in channel waters the months 
from May to September have, respectively, 6, 3, 10, 7, and 1 record, 
and there is 1 in November. Hydra is thus a late vernal and a 
summer planktont in our waters. 
Observations in the field and a cursory examination of the col- 
lections made in the backwaters have indicated that Hydra is often 
very abundant on the vegetation. It is also limnetic in habit, 
floating with the foot attached to the surface film and tentacles 
widely extended; or, without attachment, in the deeper strata of 
water. A similar limnetic habit was often observed in the case of 
Hydra in channel waters, especially on still warm days when the 
surface was unruffled. 
Hydra was generally more abundant in the plankton in May or 
in early summer. The maximum record in channel waters was 
3,200 per m.? on July 21, 1897, the error of dilution being, however, 
large in this record. In Quiver Lake on May 8, 1896, a maximum 
record of 5,335 per m.* was made, the error of dilution being very 
small. This was during a vernal plankton pulse (8.14 cm.® per m.’) 
in these waters, when the food of Hydra was present in considerable 
abundance. 
Hydra viridis L. was seen frequently in spring-fed backwaters 
and in laboratory aquaria, but was never recognized in plankton 
collections made in channel or backwaters. The limnetic habit 
noted in H. fusca was not observed in the case of this species. 
PLATYHELMINTHES. 
TURBELLARIA. 
Numerically and from the volumetric standpoint the Turbellaria 
are not of great significance in the plankton of fresh waters as a rule. 
However, in some seasons and under certain conditions Stenostoma 
becomes very abundant, as, for example, in autumn months in back- 
waters, and generally where decaying vegetation abounds. In the 
autumn of 1895 the plankton in the relict pools of Flag Lake consisted 
almost entirely of Synura uvella, Stenostoma leucops, and Entomos- 
traca. 
