Notes on the Cercariae of the Bitter Root Valley, Montana

Abstract

Before the work of Cort (1915) only isolated accounts of North American Cercariae had been published.Most of these lacked the detail necessary to distinguish species of the same groups which bear a superficial resemblance to one another.The general idea which Charles Sedgwick Minot voiced is just as true for larval trematodes as for any other larvae, when he said "It is not true that embryos are alike ; on the contrary, they show class, ordinal, and generic differences from one another.''This has been the case with the trematode forms that have come under the observation and consideration of the writer.Some details of difference are visible from a study of the living animals.Other points of differentiation require a specific, altho not unusual technic.During a two-years residence at Missoula, Montana, the writer became acquainted with the fauna of the Bitter Root Valley.One of the striking features of its fauna is the small number of species, altho the number of individuals of each species is large.In contrast with this fact is the large number of parasites found in the aquatic fauna of the region.Thru the courtesy of Mr. Bryant Walker of Detroit, Michigan, who has identified shells from some fifteen collections, the writer has ascertained that the gasteropod fauna of the vicinity consists of three species, Lymnaea proxima Lea, Physa gyrina Say, and Planorbis trivolis Say.Thirteen species of cercariae have been secured from these snails, species embracing three groups of Digenea.In addition, a fourteenth species, a Diplostomulum, has been found in the squawfish, Ptychocheilus oregonensis Richardson.Of these fourteen, two are Monostomata, two are Holostomata, and the remaining ten belong to the Distomata.The writer wishes to take this opportunity to thank Professor Henry B. Ward for many valuable suggestions, and to express his gratitude to Mr. Norbert Sager for faithful collection of material