Juday-—Quantitative Studies of Fauna in Lake Mendota. 475 
before pupation. In August and in early September the larvae 
have the appearance of being smaller in size than the winter larvae, 
and this is confirmed by the weights. At the height of the pupating 
season the summer larvae pupate when they are distinctly smaller 
than the winter larvae. 
The live weight of the pupa is somewhat greater than that of 
the larva of the same date, but its dry weight is nearly twice as 
much as that of the larva. This marked difference in dry weight 
is probably due to the presence of a larger amount of chitin in the 
pupa. Both the water and the ash content of the pupa are smaller 
than in the larva. 
The adults yielded a much smaller live weight than either the 
larvae or the pupae, but they possessed a much smaller percentage 
of water. Their dry weight was smaller than that of the pupae 
but larger than that of the larvae. The adults were obtained from 
a large swarm on June 29, 1918, when pupation was very active, 
but there was no means of ascertaining their age. Since, presum¬ 
ably, the adults do not take food, their weight will decrease with 
age, and the adults of this form live from three to five days. The 
percentage of ash was about the same in the adults and pupae, but 
in both it was distinctly lower than in the larvae. 
There is more or less overlapping of the summer broods, which 
makes it difficult to estimate the production during this season, 
but the winter crop of larvae may be estimated with some degree 
of accuracy. During this investigation twenty-two different hauls 
were made at the five regular stations during the month of Novem¬ 
ber, and these samples gave an average of 17,350 Corethra larvae 
per square meter. Five samples were also obtained in the month 
of December, and they gave an average of 21,900 individuals per 
square meter; four of these samples, however, were obtained at 
station II, which usually gave a larger yield than the other sta¬ 
tions. On a conservative basis, then, the early winter population 
of Corethra larvae may be estimated as about 18,000 individuals 
per square meter in the deep-water zone of Lake Mendota. Be¬ 
tween October and May the average live weight was 3.1 milligrams 
per larva and the dry weight 0.266 milligram. Applying these 
weights to the above population gives a live weight of 558 kilo¬ 
grams of Corethra larvae per hectare (497 pounds per acre) and 
a dry weight of 47.9 kilograms per hectare (42.7 pounds per acre). 
This estimate does not take into consideration the summer gener¬ 
ations, of which Muttkowski (4) says there may be two. Since 
