352 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
insect larvae. Plainly, therefore, the presence of falls on Lewis Eiver, insurmountable 
by fish, must be regarded as the real reason why there are no fish in these lakes. 
In Heart Lake, on the other hand, there are three or four species of fish, viz, the 
trout (8almo myldss), the chub {Leuciscus atrarius), the sucker {Catostomus ardens), 
and iirobably the blob {Gottus bairdi), all common species in the Eocky Mountain 
waters. This fish fauna is therefore what we might expect to find in thedake. 
In Yellowstone Lake there is but one species of fish, viz, the trout {Salmo mykiss), 
identical with the trout of the waters on the western side of the continental divide. 
The lake was found teeming with this species of fish and no other by the first explorers 
of the region. It is not at all probable that the lake was stocked by the aborigines, 
and the explanation given by Dr. Jordan is doubtless the correct one, namely, that 
the trout gained access to the waters of the Upper Yellowstone through Two-Ocean 
Pass, where the waters of the Yellowstone and the Snake arise from the same swampy 
meadow on the great continental divide. Prof. F. V. Hayden has shown (Bull. U. S. 
Geological Survey, vol. v, No. 2, “The so-called Two-Ocean Pass”) that during times 
of high water caused by the melting snows, there is actual connection between Atlantic 
Creek, a tributary of the Yellowstone, and Pacific Creek, a tributary of the Snake. 
It seems reasonable, therefore, that the trout, an active and somewhat gamy fish and 
fond of the colder streams, should make its way over the divide, while it would be 
exceedingly unlikely that the more logy sucker and chub should, under the circum- 
stances, attain a like distribution. 
Since there are no fish in Lewis and Shoshone Lakes it is obviously necessary to 
make a comparison here only between Heart and Yellowstone Lakes. 
The invertebrate life oP these lakes, while aifording one or two interesting con- 
trasts, presents no differences that would have any bearing on the presence or absence, 
abundance or scarcity of parasites. There is but little difference in elevation. Heart 
Lake being 7,469 and Yellowstone 7,741 feet above ocean level. The depth, so far as 
known, is much the same, although the Yellowstone, being much the larger body of 
water, will probably be found to have the greater depth. A depth of 146 feet was 
obtained at a distance of about 800 feet from the west shore of Heart Lake, where the 
bottom temperature was 40° F. A depth of 159 feet was obtained on the west arm of 
Yellowstone Lake at a distance of 2,000 feet from the shore, the temperature at bottom 
being 42° F. A depth of 195 feet was found at a distance of about a mile from shore at 
the north end of the lake. The temperature of the surface water varied with the 
time of day, but was practically the same in the two lakes. Near shore, at our camp 
on the west arm of the Yellowstone, on August 2, at 9 a. m., the surface tempeijature 
was 54° F. So far as the temperature of the lake water is concerned and the inverte- 
brate life of the two lakes, the fish in Heart Lake and those in Yellowstone Lake are 
living under substantially similar conditions. Whatever influence the presence of 
warm water from hot springs and geysers exerts, the conditions are practically the 
same, since each has geyser and hot spring regions on its borders and each receives 
warm tributaries from such regions. 
I think it likely that after all the only difference between the two lakes, that 
touches this question, lies in the fact that, while in Heart Lake the trout are associ- 
ated with the chub and the sucker, and consequently suffer or profit as the case may 
be by the mutual reaction which this association implies, in the Yellowstone they are 
alone and neither profit by the presence of another species, which they might use for 
