9] UFE HISTORY OF TREMATODES— FAUST 9 



potassium acetate. Some specimens were fixed without any acid fraction in 

 the reagent in order to preserve the excretory granules. These granules, as 

 well as the mucoid cyst membrane of the encysted worm, gave beautiful 

 biuret and xanthoproteic reactions, suggesting a tyrosine compound. 



BIOLOGY OF THE BITTER ROOT VALLEY 



The snails commonly found in the Bitter Root valley are Physa gyrina 

 Say, Lymnaea proxima Lea., and Planorbis irivolvis Say. They have been 

 identified by Mr. Bryant Walker of Detroit, Michigan. All of these snails 

 were collected from the lower part of the valley, but Planorbis trivolvis was 

 not found in the upper reaches of the river. These mollusks are the hosts 

 of the trematodes considered in this paper. 



Two facts stand out predominantly in the study of these parasites: the 

 large munber of species of trematodes in the snails in the limited range of the 

 valley, and the high per cent of infection both among individuals of a species 

 and within the individual of the species. 



There have been found in a single season's collection thirteen trematode 

 species in the snails of the valley, and one larval trematode in the squaw-fish, 

 Ptychocheilus oregonensis Richardson. A total of fifteen collections of snails 

 was made during the fall of 1916 and four collections during May 1917. 

 Seventeen of these collections contained trematode infection. Lymnaea 

 proxima was taken eight times from five different localities, Physa gyrina 

 was taken eleven times from eight different locaHties, and Planorbis trivolvis 

 was taken three times from two localities (Table I, see next page). 



The infection record shows that the host is not specific. In the infection 

 of mollusks with Cercaria pellucida the host around Buckhouse Bridge was 

 Physa, while that up the valley was Lymnaea. Cercaria gracillima was found 

 both in Physa and in Lymnaea in the region of Buckhouse Bridge from 

 different collections. Cercaria trisolenata was found both in Physa and in 

 Lymnaea in the region of Buckhouse Bridge and in the vicinity of Fort 

 Missoula. While no parasite species was found in more than two of the three 

 snails common in the valley, there is reason to beUeve that the third species 

 of snail might be the host under proper conditions. This view is contrasted 

 with that of Thomas (1883:106) who found that only one EngHsh moUusk, 

 Lymnaea trunculata, "could serve as an intermediate host to the liver fluke," 

 altho this writer suggested that other species of snails must serve in other 

 countries as hosts to the worm. This preference for a particular moUusk in a 

 particular locality, coupled with the abihty to select a different molluscan host 

 in another locality, has been found to hold true not only for Fasciola hepatica, 

 but also for Schistosoma haematobium (Leiper, 1916) and S. mansoni (Leiper, 

 1916; Lutz, 1916; Iturbe and Gonzalez, 1917). When two hosts so different 

 structurally as Physa and Planorbis are equally heavily infected, it seems 

 evident that the stimulus to which the miracidium of the fluke responds can 



