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FISH ENTOZOA FROM YELLOWSTONE PARK. 5AT 
The admirable researches of Donnadieu on the ligula of the European 
tench show that 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 specimens of L. catostomi showed comparatively 
slight difference in apparent age points to the conclusion that the 
period of infection is brief. Itis 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 thisregion. 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 
egg. If these parasites 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 29 I threw into the lake a large number of 
these parasites, and on the following day, about noon, caught a chub 
(Leuciscus atrarius) near the place where: the ligule had been thrown. 
The alimentary canal of the chub was filled from one end to the other 
with ligule 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. 
DIBOTHRIUM CORDICEPS Leidy. 
A description of this species by Dr. Joseph Leidy was published in 
the Preliminary Report 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, pls. XXV-XXVII); and 
of the adult stage in ‘“‘A contribution to the life history of Dibothrium 
_cordiceps,” etc. (Bull. U. 8. Fish Commission, 1x, for 1889, pp. 337-358, 
pls. 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 (Pelecanus 
erythrorhynchius), 
