Muttkowski—The Fauna of Lake Mendota. 417 
of stones. For respiration they have branched abdominal gills, 
which, however, unlike the trilobitic Parnid sp. just mentioned, 
are not retractile (the other also possesses a retractile anal tuft 
of tracheae). 
In late July the larvae emerge in enormous numbers from the 
lake and pupate in the moist soil 'under the rocks near the wa¬ 
ter margin. In 1915 pupation took place immediately before 
a rise of 17-20 cm. in the lake level, which resulted in the 
death of great numbers of the pupae, since the latter, like the 
adults, are terrestrial. If it were not for the fact that the 
year-old larvae remained in the lake—the species has a biennial 
cycle—the lake population of the form would be considerably 
diminished. 
The adults are terrestrial. Copulation takes place on land. 
Oviposition may take place at the water ’s edge, on stones in 
the water, or the female may descend some distance into the 
water to lay her eggs. 
Locally the larvae may be exceedingly abundant. On one 
occasion, in July, 1915, I found over 800 specimens in an area 
of one square meter at Parwell’s Point. Yet curious to say, 
I have no records of their being eaten by fish. Whether this is 
due to their excellent protective adaptation or to some other 
factor remains to be seen; I have, however, on several occa¬ 
sions, found small leeches attached to the underside of the lar¬ 
vae. 
A problem of distribution was revealed during some dredg¬ 
ings made on the shallow reefs in the eastern portion of the 
lake. Bach of the reefs is over half a mile from the nearest 
shore, hence it is unlikely that larvae might migrate to them. 
But the dredge contents showed that the larvae were quite 
abundant on one of the reefs. Since the reefs are covered 
with at least 3 meters of water at their highest points, the 
assumption of drift as an explanation for the distributional 
“island” is out of the range of probability. How the larvae 
got there, how they pupate (pupae being terrestrial), etc., re¬ 
mains a riddle for the present. 
27—S. A. L. 
