354 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
ally exposed to the source of coutagion or parasitism with no respite, with no seasons 
of relief except what may be incident to the nature of the germs. It follows, therefore, 
from the peculiar conditions surrounding the trout of Yellowstone Lake, that if there 
is a cause of parasitism present in successive years the trout are more liable to become ' 
infested than they would, be in waters where they had a more varied range. Trout 
would become infested earlier and in greater relative numbers, and the life of the 
parasites themselves, that is, their residence as encysted worms, must be of longer 
duration than would be the rule where the natural conditions are less exceptional. 
Again, in such cases of parasitism as that under corisideratiou, where the parasite 
is a larval cestod and the intermediate host the only animal of its kind in this region, 
the final host is more likely to partake of parasitized food than he would be if part of 
his food consisted of other species of fish not harboring this parasite. For example, 
it may be supposed that pelicans, when in tbe vicinity of Heart Lake, feed indiffer- 
ently on trout, chubs, and suckers. Even if the trout stood an equal chance with the 
others of being eaten, which is hardly to be supposed since it is a more active fish than 
they, it would then constitute but one- third of the food of the pelican. The chances 
of the pelican’s becoming parasitized would therefore be diminished to one-third what 
they would be from its diet on Yellowstone Lake. But with this diminished parasit- 
ism in the final host would go a smaller amount of eggs from the adult parasites to be 
disseminated where the fish are likely to get them. 
As a matter of fact there can not be this diiference between the parasitism of the 
trout of Yellowstone and of Heart Lake, as these bodies of water are so near together 
that the pelicans found on the one are the same individuals which visit the other. 
While in camp on Heart Lake, and also on the west arm of the Yellowstone, we 
saw several pelicans, but secured no specimens. After we reached the hotel on Yellow- 
stone Lake I made an excursion to the southeast arm of the lake for the purpose of 
securing specimens of these birds. The southern end of the lake is as yet almost never 
visited, and we discovered that the pelicans not only roost, as was known, but also 
breed on the small islands there. Four pelicans were obtained on Molly Island in 
a deep bay on the west side of the southeast arm of the lake. Our party were in 
two rowboats, Mr. F. D. Booth, with our only shot-gun, in company with Messrs. 
Thompson and Coughlin, visited the island and shot the birds for me. As we had found 
the pelicans thus far rather shy, I and my companion, Mr. Curl, did not approach the 
island, but rowed across to the northern shore, keeping well outside of the island for 
fear of frightening any birds which might be there. I thus, much to my subsequent 
regret, missed seeing the breeding- place of these interesting birds. Mr. Booth reported 
that they could easily have secured a boat load of the birds if it had been deemed 
necessary. He estimated that there were at least five hundred pelicans, young and old, 
on the island, less than one hundred of which were young. The young were large 
enough to take care of themselves by running and swimming, but could not fly much. 
The old birds refused to leave the neighborhood of their young and so could readily be 
shot. The specimens secured were all adults and measured 92, 96, 97, and 98 inches, 
respectively, from tip to tip of the wings. They had an exceedingly rank, fishy smell, 
and the gentlemen who visited the breeding-place bore testimony in a variety of select 
epithets that the smell of the place was horribly bad. The result of an examination 
of these birds has already been given. Many gulls were also found breeding on this 
island. 
