SOME AQUATIC INVERTEBRATES THAT LIVE UNDER 
ANAEROBIC CONDITIONS. 
CHANCEY JUDAY. 
[Biological Notes from the Laboratory of the Wisconsin Geological and Natural 
History Survey. II.] 
During the past two years, many observations have been 
made on various Wisconsin lakes for the purpose of determin¬ 
ing the amounts and kinds of gases dissolved in their waters. 
Particular attention has been given to the dissolved oxygen, 
since it plays such an important role in the metabolic processes 
of living organisms, in order to see how these organisms affect 
its amount and distribution, and, in turn, how its amount and 
distribution affect the life of the lakes. Birge 1 has given a 
general summary of some of the results that have been ob¬ 
tained. These studies have been carried on by the Wisconsin 
Geological and Natural History Survey, and a detailed report 
of the results is now being prepared for publication. 
It is the purpose to deal here with only one phase of the sec¬ 
ond problem indicated above, that is, how the animal life is 
affected by the absence of dissolved oxygen. Several lakes have 
been found in which the lower water is devoid of free oxygen 
for a considerable period during the summer. In some lakes 
this condition may exist from the middle or last of May until 
the early part of October, while in others it may not last more 
than one or two months. This lower stratum of water is 
cooler than the upper, hence its density is greater. Because 
i Birge, Trans. Amer. Fish. Soc., 1906, pp. 141-161. 
