FISH ENTUZOA FROM YELLOWSTONE PARK. 547 



Tke aclHttirablo r<^s»ear«lies of Dounadieu on tliw liijuhi of tke European 

 tench show tliat the time during- which the parasite lives in the abdom- 

 inal cavity of the fish is variable, but is generally limited to two years. 

 Most frequently it attains its maximum development at the end of the 

 second year. 



The fact that the specii'.ums of L. vatostomi showed comparatively 

 slight difference m apparent age points to the conclusion that the 

 period of infection is brief. It is probable that the final host is one, 

 or possibly more than one, of the migratory aquatic; birds, such as the 

 heron, pelican, larus, merganser, etc., which are summer residents or 

 visitors in this region. The abundance of the parasites is doubtless due 

 to the warm water in the streams fed by thermal springs, which fur- 

 nishes conditions favorable to the development of the embryos from the 

 bgg. If these i;)arasites ever normally make their escape from their 

 intermediate host the fish, as stated by European observers, the 

 chances of their being swallowed by a bird are very few, since they are 

 eaten with avidity by fish, in whose intestine, however, they do not 

 mature. 



On the evening of July 2!) I threw into the lake a large number of 

 these parasites, and on the following day, about noon, caught a chub 

 {Leuciseus atrarim) near the place where the liguhe had been thrown. 

 The alimentary canal of the chub was filled from one end to the other 

 with liguhe in various stages of digestion. In the intestine they were 

 reduced to a white chyle with recognizable fragments, and even in the 

 stomach they were corroded and fragmental. 



DiBOTHiuuJi cop.DiCEi's Leidy. 



A description of this species by Dr. Joseph Leidy was published in 

 the Preliminary Eeport of the U. S. Geological Survey of Montana and 

 adjacent territory (Hayden, 1871, pp. 381, 382). Some account of the 

 anatomy of the larval stage was given in my paper entitled, " On two 

 species of Larval Dibothria from the Yellowstone National Park (Bull. 

 U. S. Fish Commission, ix, for 1889, pp. 72-76, pis. xxv-xxvii); and 

 of the adult stage in "A contribution to the life history of Dlbothrium 

 cordkeps^^'' etc. (Bull. U. S. Fish Commission, ix, for 1889, pp. 337-358, 

 pis. CXVII-CXIX.) 



Larval stage: In the rocky mountain trout {Salmo mykiss), in cysts 

 and free in the abdominal cavity; also often migrating into the flesh 

 of these trout in the Yellowstone Lake. 



Adult stage: Intestine of the American white pelican {Pelecanns 

 crijthrorhynchun). 



