421 
especially into the branches of the Kaskaskia where these come near- 
est to the Embarras, and into those of the Big Vermilion of the IIli- 
nois which are nearest to the Little Vermilion of the Wabash. Some 
species, however, remain carefully within the tributaries of the Wa- 
bash system. 
It seems possible that this appearance of an approach to the state 
and entrance upon its territory from opposite directions is not alto- 
gether deceptive, and that the annual movements of the fishes of the 
state, up the streams at the time of the spring floods, downwards 
with the recession of the waters, and still farther downwards, for 
many species, into deeper water in the winter, may take these two 
contingents of our fish population in opposite directions, from and 
towards local centers of population for the species, situated on oppo- 
site sides of the state. Whether and where such local centers of 
population actually exist, is a question which can not be answered 
definitely for lack of numerical or statistical data in the faunal 
lists and other literature of geographical distribution for the sur- 
rounding states. If they exist, the Wabash fishes would constitute 
one such system, and those of the Mississippi and its tributaries, 
another. 
If we may speculate still further upon this subject, we may per- 
haps surmise that a general critical analysis of the fish population of 
the larger area of which Illinois forms the central part, would enable 
us to distinguish fairly well-defined districts, each with its charac- 
teristic assemblage of prevalent species, so associated and ecologic- 
ally related as to form a balanced assemblage of species, all so ad- 
justed to each other and so advantageously placed in their environ- 
ment as to constitute a closed system, which the characteristic 
species of adjacent areas can not enter, or in which they can not 
permanently remain. 
DISTRIBUTION CHIEFLY IN THE OHIO DRAINAGE 
Brindled stonecat Pirate-perch 
Green-sided darter Notropts illecebrosus 
Boleichthys fusiformts Ericymba buccata 
Chub-sucker Long-eared sunfish 
DISTRIBUTION CHIEFLY IN THE Mississtpp1 DRAINAGE 
Short-nosed gar White bass 
Stonecat Yellow bass 
Lake carp Common bullhead 
Notropis cayuga Short-headed red-horse 
