12 Wisconsin Academy of Sciences, Arts and Letters. 
have a respiratory function or not. In this case, however, one 
can readily see how they may fulfill a very important respira¬ 
tory function by serving as reservoirs for oxygenated gas. 
This would enable the larva to remain in water that is devoid 
of free oxygen for a considerable period of time without incon¬ 
venience. Since it is a very good swimmer, it can readily 
reach water that possesses some free oxygen whenever a new 
supply is needed. It is not yet clear just why the larva should 
choose to remain down in this region during the day. It seems 
to react negatively to light, as it moves down into the lower 
water very early in the morning and remains there during the 
day. At night, however, it moves up into the upper water and 
is very often found at the surface. 2 3 One would scarcely ex¬ 
pect light alone, however, to cause the animal to descend to a 
depth of 12 or 15 meters, since the transparency of the water 
is tolerably low, a Secchi’s disk generally disappearing from 
view at a depth of two or three meters. But larval Corethra is 
the only form which inhabits this region, so it is entirely free 
from enemies there. It seems probable that this may be one 
of the reasons why it remains there during the day, when it 
would suffer most from animals which prey upon it. At night, 
when it would be comparatively free from the attacks of ene¬ 
mies, it rises into the upper water where it may obtain an abun¬ 
dance of oxygen and food, both of which are absent from the 
lower water. 
Several forms were also found in the muddy ooze at the bot¬ 
tom of the lake, although no free oxygen was present there. 
The mud was obtained by means of a pump and hose and was 
pumped through bottles that could be sealed and kept air-tight 
while they were being conveyed to the laboratory for study. 
Thus the material did not come into contact with the air until 
removed from the bottles for examination. Protozoa were 
found to be the most common forms. Living, active repre¬ 
sentatives of the following genera were noted:— Pelomyxa, Dif - 
flugia, Colpidium , Gyrocorys, Peranema, Coleps , Paramecium? 
2Birge, Trans. Wis. Acad. Sci., Arts and Letters, vol. 11, p. 410. 
1897. 
s Juday, Ibid., vol. 14, p. 556. 1904. 
