Juday and Wagner—The Distribution of Fishes. 19 
should not hold true for the entire summer. This habit, then, 
of remaining in the cool, lower water during the summer means 
that this region of a lake must be habitable for the trout at this 
period or it cannot be successfully acclimated. The chief factor 
in making this region habitable is dissolved oxygen. If the free 
oxygen entirely disappears from the cool water in summer, or 
if it is reduced to an amount so small that it will not supply 
the needs of the fish, it cannot occupy this region, and there¬ 
fore will not thrive in such a lake. This readily explains why 
the efforts to stock Kawaguesaga Lake with Mackinaw trout 
proved unsuccessful. As stated above, it was found that all the 
cool, lower water of this lake was devoid of free oxygen in 
early September, and this condition doubtless exists for a con¬ 
siderable period each summer. The trout is unable, therefore, 
to occupy the cool water, and this makes conditions so unfavor¬ 
able that it cannot maintain itself in the lake. On the other 
hand, the lower water of Trout Lake contained enough dissolved 
oxygen to supply the trout’s needs, and trout are found here 
in abundance. They are native fish, not the result of artifi¬ 
cial planting. j 
In order to study the effects of such water on active fishes, 
some experiments were performed on perch (Perea flavescens ) 
and crappies ( Pomoxis ), as they are very hardy fishes. Some 
of the lower water in Mendota which was free from dissolved 
oxygen was pumped up into aquaria and specimens of these 
fishes were immediately placed in these aquaria. In every case 
they died in a very short time, the length of time varying some¬ 
what for the different individuals. In general, also, the perch 
lived a little longer than the crappies. These results only con¬ 
firmed what had been taken for granted before performing the 
experiments, that is, that the lower water is uninhabitable for 
fishes when it is devoid of free oxygen. Their inability to oc¬ 
cupy this region means a very considerable restriction in their 
vertical distribution in some lakes. In some of the smaller lakes 
which are well protected from winds and which contain a con¬ 
siderable amount of decaying organic matter, the dissolved oxy¬ 
gen may entirely disappear at a depth of 5 or 6 meters in Au¬ 
gust, so that the fishes would be limited to a warm, upper stra- 
