Juday—Invertebrates Living under Anaerobic Conditions . 15 
the parasitic worms have adapted themselves to a life under 
anaerobic conditions. It has been found that some of the par¬ 
asitic forms living in the absence of free oxygen have a very 
high glycogen content, and it would be interesting to know 
whether this is true of these non-parasitic forms, and also 
whether there is any change in the relative amount of glycogen 
during the aerobic and anaerobic periods. 
Chaetonotus, was always active. Candona kept itself buried 
in the mud and seemed to show very little activity, but when 
placed in aerated water it soon became much more active. 
Chironomid larvae were scarce, and no specimen of them was 
found in the jars on which observations were made. Corneo- 
cyclas remained quiescent with the valves tightly closed. Some 
of the jars were kept under observation for two weeks and no 
living specimens were ever found with the valves open. The 
mud was also carefully examined for indications of activity, 
but no evidences of it were found. But when removed from 
the jars and placed in aerated water, or when the contents of 
the jars were poured into crystallizing dishes and exposed to 
the air, they soon became very active. These results seem to 
indicate that this mollusk remains quiescent or dormant dur¬ 
ing the period when the muddy ooze at the bottom of the lake 
contains no dissolved oxygen. This means, then, that this 
“latent life” condition continues for a period of about three 
months each summer in Lake Mendota. In 1906, the earliest 
date on which the bottom water was found to be free from dis¬ 
solved oxygen was July 9, and it remained in this condition 
until October 9. This covered most of the time which one 
would naturally consider most favorable for growth and 
activity, because of the higher temperature of the water, but 
Corneocyclas seems to have adapted itself to a quiescent period 
at this time because of the lack of dissolved oxygen. The time 
at which it reproduces has not been determined. Neither has 
there been any opportunity as yet to ascertain how widely it is 
distributed over the bottom of the lake. It may extend into 
the shallower water, where it would find a sufficient amount 
of free oxygen to enable individuals in this region to continue 
their activities during the summer. If reproduction takes 
