43, 
The vast increase in numbers and weight of midge larvae in the 
muds of Peoria Lake between 1915 and 1920, the comparison being of 
July—September collections for both periods, goes far in some portions 
of the range toward making up the losses in the small Mollusca. While 
the average number of young midges taken to the square yard between 
Chillicothe and the foot of the lake was less than 10 in the summer of, 
1915, in 1920 it had risen for the whole lake to 318; while in the channel 
and 417-ft. zone of the upper lake, between Chillicothe and Spring Bay, 
numbers per yard were 1216 and 554. Again, while in 1915 the greatest 
weight per acre figured for Chironomidae in a subdivision of Peoria Lake 
(the 4—7-it. zone of the middle lake) was only 7 pounds, and the average 
for all zones and all subdivisions in 1915 was only 1.4 pounds, in 1920 the 
average weight had risen in the channel and 4—7-ft. zones of the upper 
lake to 182 and 128 pounds respectively, and for all subdivisions and all 
zones to 83.3 pounds, or 59.5 times the average valuation figure of 1915. 
When we compare the weight of the Chironomidae with the weight of 
the average total haul we find that the largest catches in Peoria Lake in 
1915 ran less than 6 per cent. Chironomidae, most of the collections, in 
fact, running less than 3 per cent. In 1920, on the other hand, we find 
the Chironomidae making up from 21 to 42 per cent. of the average total 
weight of collections in the channel between Chillicothe and Peoria, and 
from 70 to 96 per cent. in the 1—3-ft. and 4—7-ft. zones. 
Mince LAarvAE (CHIRONOMIDAE) OF Bortrom Mups, 
CHILLICOTHE TO Foot or Peoria Lake, 1915 anv 1920 
1. Number and weight per unit of bottom area 
Channel | 4-7-ft. zone 1—3-ft. zone 
1915 1920 | 1915 1920 | 1915 1920 
Upper lake 2 1216 13 554 12 0 
Average No. 
per sq. Middle lake 10 36 21 201 5 84 
yard | 
Lower lake 0 244 | 0 332 0 198 
: | 
Upper lake 0.2 182 | 4.2 128 | 2 0 
Average | 
pounds Middle lake 1 5 | 7 51 3 42 
per acre | 
Lower lake 0 86 | 0 132 0 24 
Average weight per acre, all channel collections, 1920, 89.2 lbs. 
i <3 “« «all 4—7-ft.-zone collections, 1920, 101.0 lbs. 
vs Se « «all 1—3-ft.-zone collections, 1920, 27.6 lbs. 
Average weight per acre, all collections, all zones, 1920, 83.3 lbs. 
Average weight per acre, all collections, all zones, 1915, 1.4 lbs. 
