14 Wisconsin Academy of Sciences, Arts and Letters. 
cardiformis for fifty days in a medium that contained no free 
oxygen when he fed them on egg albumen. hTo chlorophyl was 
found in any of the Protozoa that were obtained from the bot¬ 
tom of Lake Mendota, so that they could not have obtained 
free oxygen by splitting up C0 2 . Even if they had contained 
chlorophyl, the intensity of the light at a depth of 20 or 22 
meters jvas undoubtedly not sufficient to make it serviceable, 
because the transparency of the water was low. The medium 
in which these Protozoa lived was not only free from dissolved 
oxygen, but the water also contained about 7.5 cubic centi¬ 
meters of free C0 2 per liter and about 5 or 6 cubic centimeters 
of CH 4 . 
Some higher invertebrates were also found in the mud. The 
worms were represented by specimens of Tubifex, Limnodrilus 
and Anguillula; the rotifers by Chaetonotus; the Crustacea by 
an Ostracod belonging to the genus Candona ; the insect larvae 
by a large red Chironomid larva; and the mollusca by Corneo- 
cyclas idahoensis. 
In order to study the activities of these forms while they 
were in a medium which contained no dissolved oxygen, some 
of the muddy water containing them was pumped into glass 
jars that could be sealed and kept air-tight. Great care was 
exercised in taking the samples so as to keep the medium free 
from dissolved oxygen. The muddy water was pumped 
through the jars so that they could be thoroughly flushed and 
all of the material removed that had been exposed to the air. 
After being sealed, the jars were taken to the laboratory and 
placed in a refrigerator in order to keep the temperature about 
the same as that of the mud in the bottom of the lake. They 
were kept at a temperature of 13° to 15° C., which was 1.5° 
to 2.5° higher than the temperature of the mud in the lake at 
the various times the samples were taken. The jars were re¬ 
moved from the refrigerator from time to time and carefully 
examined to see how active the various animals were. The 
worms were as active under anaerobic conditions as they were 
when placed in aerated water. So far as could be determined, 
they were not affected in the least by the lack of free oxygen. 
This result should probably have been expected, as so many of 
