348 Diseases of Fishes 



It may be inferred from the foregoing statements that the rea- 

 son why the parasite of the trout of Yellowstone Lake migrates 

 into the muscular tissue of its host must be found in the fact 

 that the life of the parasite within the fish is much more pro- 

 longed than is the case where the conditions of life are less 

 exceptional. 



" The case just cited is probably the most signal one of 

 direct injury to the host from the presence of parasites that 

 I have seen. I shall enumerate more briefly a few additional 

 cases out of a great number that I have encountered in my 

 special investigations on the entozoa of fishes for the U. S. Fish 

 Commission." 



Many worms of this type abound in codfishes, bluefishes, 

 striped bass, and other marine fishes, rendering them lean and 

 unfit for food. 



The Heart Lake Tape-worm. Another very interesting case 

 of parasitism is that of the large tape-worm (Ligula catostomi) 

 infecting the suckers, Catostomus ardens, in the warm waters 



FIG. 230. Sucker, Catostomus ardens (Jordan & Gilbert), from Heart Lake, Yellow- 

 stone Park, infested by a flatworm, Ligula catostomi Linton, itself probably a 

 larva of Dibothrium. (After Linton.) 



of Witch Creek, near Heart Lake, in the Yellowstone Park. Of 

 this Dr. Linton gives the following account : 



"In the autumn of 1889 Dr. David Starr Jordan found an 

 interesting case of parasitism in some young suckers (Catos- 

 tomus ardens} which he had collected in Witch Creek, a small 

 stream which flows into Heart Lake, in the Yellowstone National 

 Park. Specimens of these parasites were sent to me for identi- 

 fication. They proved to be a species of ligula, probably iden- 

 tical with the European Ligula simplicissima Rud., which is 



