8 Wisconsin Academy of Sciences, Arts and Letters . 
this species is a limnetic form during the summer. It is clear, 
then, that if these cocoons belong to this species, as they appear 
to do, part only of the members of the spring broods can be¬ 
come encysted, and other individuals must go on reproducing 
during the summer. Whether the fall broods come from the 
encysted individuals or from the others is unknown. It is 
hard to see why encystation should take place at all in this lake. 
It is to be said that, if our species is the same as the Euro¬ 
pean form, its habitat is different. Schmeil (’92, p. 79) speaks 
of it as coming from “Teichen” and “Wassertiimpeln,” and 
other authors give a similar habitat. Marsh, on the contrary, 
speaks of it as characteristic for the Great Lakes and found in 
comparatively few inland waters. 
Our knowledge of the species, its distribution and its habits, 
is so scanty and fragmentary that no interpretation of the facts 
here set forth is possible in relation to the life history of the 
species. It may be that the form is migrating from the Great 
Lakes to the smaller waters and is acquiring the power of en¬ 
cystation in adaptation to the ordinary summer conditions of 
such lakes; or the species may be moving toward the larger and 
colder bodies of water and losing, in part, in such lakes as 
Eainbow, the adaptations which were necessary in shallower 
bodies of water with more abundant plankton. 
It appears, therefore, that the encystation of Cycloys occurs 
in lakes of very different types, both as regards temperature 
and the oxygen content of the lower water. It is at present 
impossible to correlate the phenomenon with any definite physi¬ 
cal change in the lake, or with any known condition of the 
lower water in summer. If the cocoons all belong to one 
species, as they appear to, part of the individuals in certain 
lakes must become encysted and part remain active. It is cer¬ 
tain that the phenomenon is not local, as cocoons have been 
found from six lakes situated in the southern, northeastern and 
northwestern parts of Wisconsin. The most distant lakes lie 
at angles of a triangle whose sides are about 225, 190 and 115 
miles long. 
A number of other interesting questions remains unsettled. 
Among these are the nature and origin of the glutinous material 
