Diseases of Fishes 345 



human tape-worm (Bothriocephalus tcenia) has been got from 

 eating the flesh of the European tench (Tinea tinea). 



The Worm of the Yellowstone. The most remarkable case 

 of parasitism of worms of this type is that given by the trout 

 of Yellowstone Lake (Salmo clarki). This is thus described by 

 Dr. Linton: 



" One of the most interesting cases of parasitism in which 

 direct injury results to the host, which has come to my atten- 

 tion, is that afforded by the trout of Yellowstone Lake (Salmo 

 clarki). It was noticed by successive parties who visited the 

 lake in connection with government surveys that the trout 

 with which the lake abounded were, to a large extent, infested 

 with a parasitic worm, which is most commonly in the abdom- 

 inal cavity, in cysts, but which in time escapes from the cyst 

 and tunnels into the flesh of its host. Fish, when thus much 

 afflicted, are found to be lacking in vitality, weak, and often 

 positively emaciated. 



"It was my good fortune, in the summer of 1890, to visit 

 this interesting region for the purpose of investigating the para- 

 sitism of the trout of Yellowstone Lake. The results of this 

 special investigation were published in the Bulletin of the 

 U. S. Fish Commission for 1889, vol. ix., pp. 337-358, under the 

 title' A Contribution to the Life-history of Dibothrium cordi- 

 ceps, a Parasite Infesting the Trout of Yellowstone Lake.' 



"I found the same parasite in the trout of Heart Lake, just 

 across the great continental divide from Yellowstone Lake, but 

 did not find any that had tunneled into the flesh of its host, 

 while a considerable proportion of the trout taken in Yellow- 

 stone Lake had these worms in the flesh. Some of these worms 

 were as much as 30 centimeters in length when first removed; 

 others which had lain in water a few hours after removal before 

 they were measured were much longer, as much as 54 centi- 

 meters. They are rather slender and of nearly uniform size 

 throughout, 2.5 to 3 millimeters being an average breadth of 

 the largest. I found the adult stage in the intestine of the 

 large white pelican (Pelecanus erythrorhynchus) , which is abun- 

 ant on the lake and was found breeding on some small islands 

 near the southern end of the lake. 



" In the paper alluded to above I attempted to account for 



