64 
In Thompson, Dogfish, and Liverpool lakes in September, 1920, not 
only was it true that not a single definitely recognized clean-water chiro- 
nomid of the previous period (1913—1915) was found surviving in the 
larval or pupal stage in the muds, but, as well, the lists both of new en- 
trants and survivals, of whatever habit of preference, showed up very 
meagerly both in variety and abundance as compared with the lists and 
tigures for the Peoria Lake district and the river just above Havana. 
Both in Thompson and Liverpool lakes, however, there did appear last 
year small numbers of one new form of possibly tolerant habit, this 
opinion being based only on its taxonomic nearness to Chironomus 
decorus Joh. In neither of these two lakes nor in Dogfish Lake was there 
any evidence of the recent intrusion of species of distinctly pollutional 
habit, while in the muddier portions of Quiver Lake two of the older 
clean-water Chironomidae (C. ferrugineovittatus Zett., and Palpomyia 
longipennis Lw.) that were formerly present in all the lakes of this group 
were the principal components of the 1920 chironomid population in 
September. 
The changes in total chironomid poundages since 1914—1915 in all 
of these four lakes except Quiver, quite contrary to those in the Illinois 
River opposite, are in the direction of decrease rather than increase, the 
average yields in 1920 (9 pounds per acre in Dogfish, 4 pounds in Thomp- 
son, 2 pounds in Liverpool) being in no case over 50 per cent. of the 
1914—1915 yields, and at the lowest only 5 per cent.; while they are only 
5 to 7 per cent. of the 1920 yields of Chironomidae from the river muds 
between Liverpool and Havana. The discrepancies between lake and 
river figures for immature midges in this portion of the river system, 
contrasting with essentially similar changes both in river and lake in the 
snail group, may be concerned with the fact of the greater ease of spread 
of the eggs and larvae of the midges down stream with the advance of 
pollution than by wing across the timbered ridges that separate the river 
from the lakes. At any rate, two of the principal pollutional or tolerant 
species contributing to last year’s large river poundages of Chironomidae 
just above Havana (C. plumosus Linn., and C. decorus Joh.) did not up 
to that time appear to have been successful in making the trip. 
