Juday—Quantitative Studies of Fauna in Lake Mendota. 471 
just a little more than five times as much as the small ones. For 
the dry weights, however, the ratio was appreciably less than five 
to one in both instances. It will be noted that the percentage of 
water was highest in the large individuals and lowest in the small 
ones; the same was true of the ash. 
By using the average number of larvae per square meter, 
namely, 593, the percentages of the different sizes, and their aver¬ 
age weights, we may calculate the live and dry weights of the 
chironomid population of the deep-water zone. The results of such 
a calculation are shown in table 9. While the small individuals 
were almost five times as numerous as the large ones, their live 
weight was less than one fifth as great, but their dry weight was 
slightly more than one fifth as much as that of the large ones. 
The live weight for all sizes averages a little more than 75 kilo¬ 
grams per hectare, or slightly more than 67 pounds per acre, while 
the dry weight is a little in excess of 12 kilograms per hectare (10.8 
pounds per acre). 
The larvae of Chironomus tentans are regarded as an important 
source of food for fishes, and chemical analyses were made for the 
purpose of obtaining some idea of their food value. The material 
which was used for these analyses consisted of 1,552 individuals 
ranging from 20 millimeters to 25 millimeters in length. The re¬ 
sults obtained in the analyses are shown in table 10. 
The percentage of nitrogen given in this table is exclusive of that 
in the crude fiber or chitin, namely, 0.23 per cent.; that is, the 
total nitrogen amounted to 7.59 per cent, of the dry material. 
While the percentage of nitrogen is not as high as in the larvae of 
Corethra, nevertheless it is high enough to make these chironomid 
larvae an excellent source of protein material. That is, about 46 
per cent, of the dry weight of the larvae may be regarded as crude 
protein. The fat content is rather low, namely, only 8 per cent. 
The ash in these specimens is distinctly higher than that indicated 
in table 8; this is probably accounted for by the fact that the ash 
content depends, in large measure, upon the character of the food 
that is present in the alimentary canal. 
Corethra pnnctipennis Say 
The larvae of Corethra punctipennis may be regarded as bottom 
dwellers, in part at least, since the larger ones desert the water 
entirely during the daylight hours and remain concealed in the 
