406 Wisconsin Academy of Sciences, Arts, and Letters. 
table are littoral catches made at pupation periods and of no 
value in estimating the deeper distribution. (Some of the 
catches made in the summer of 1916 by means of a clam-shell 
dredge show numbers ranging from 2,000 to 18,000 individuals 
per square meter.) 
Corethra begins to pupate about June 10th and enormous 
swarms emerge continually during the summer weeks of June 
15th to about August 20th; the numbers then decrease to Sep¬ 
tember 10th, when they become small, the last adults emerging 
about September 30th. Corethra emerges at night, beginning early 
in the evening and continuing through the night. Large 
swarms of them fly to the lights of Madison or gather in the 
tree-tops, especially in the vicinity of the lake. In the morning, 
if the lake is quiet, the females can be seen resting on the sur¬ 
face, ovipositing through the surface film. 
From observations made since 1912, it seems that there are 
about six great periods of swarming or emergence, alternating 
with an equal number of minor ‘^pulsations.’’ In each case 
the adults live about three to five days. 
The larvae, while primarily pelagic, hunt their food chiefly 
at the bottom, where they nestle into the soft ooze. The food 
consists of small worms, and the various components of the 
plankton. In Picnic Pond, where specimens of Corethra are 
quite abundant, I have watched them feed on Volvox. The 
method of feeding is curious. Bits of food are rasped off the 
prey, taken into the stomach, and digested. After digestion 
the waste is ejected through the mouth (Frankenberg 1915), 
an observation which can be easily verified. 
Transparency is the greatest protection of the larva and pupa. 
Despite this tranparency Corethra is eaten in large numbers 
by the fish of the lake, especially by the bottom feeders of the 
deeper waters. One frequently finds specimens of perch which 
have gorged themselves on Corethra larvae. 
Corethra is unique in its system of respiration. At each end 
of the body are found two twisted air-chambers, which are en¬ 
tirely detached from the surface. Their structure is tracheal, 
and they function primarily as static organs, and possibly as 
storage organs for oxygen used in respiration. The general 
tracheation is very meager and appears insufficient. In res¬ 
piration the oxygen must be taken from the water through the 
skin and carried in the blood wherever needed. In contrast 
