7] LIFE HISTORY OF TREMATODES— FAUST 



INTRODUCTION 



During a two years' residence at Missoula, Montana, from 1914 to 1916 

 the writer became acquainted with the biology of the inter-mountain region 

 of the Bitter Root valley. The heavy trematode infection of the animals 

 in this locality has led to an investigation of the life history of the trematodes 

 of the region. 



An opportunity is taken at this place to express appreciation to all who 

 have aided in this study, but especially to Professor Henry B. Ward whose 

 kindness and sincere interest have made the work possible. 



METHODS OF INVESTIGATION 



This study is confined to the trematodes infecting moUusks. The majority 

 of the collections were made by Mr. Norbert Sager of Missoula. A sketch 

 map (text-fig. 1) indicates the location of each collection. The snails were 

 shipped in damp green moss and arrived in excellent condition. 



These observations on living material gave data on the stages of develop- 

 ment within the mollusk, on the methods of loconiotion, on encystment, and 

 on the excretory system. 



The worms were removed from the infected tissue and placed in a watch 

 glass in 0.3 per cent saline solution. The change from the host tissue to the 

 sahne medium usually caused rapid movement. 



It is essential that the excretory system be studied in the living material 

 as, aside from the vesicle and the main trunks of this system, very little can 

 be made out in the preserved material. The delicate structure of the flame 

 cells and the finer capillaries makes it necessary that these organs be examined 

 in living specimens, for in fixation they are likely to collapse, even with the 

 most careful technic. 



The organs of the digestive system come out equally well in living and 

 preserved mounts. Some systems, as a rule, can be made out only from pre- 

 served and stained material. The most important of these is the genital com- 

 plex. For all ordinary purposes the material was fixed in Gilson's reagent, 

 altho equally good results were obtained from a corrosive-acetic fixing agent. 

 From the preserved material to to mounts and sections were made, using Dela- 

 field's hematoxylin and Ehrlich's acid hematoxylin as stains. A strong 

 counter-stain of eosin in the sections brought out remarkably well the nerve 

 fibers of the worms. Wax models were made of the mature and immature 

 stages of the nervous system of cercariae and parthenitae. 



Care was taken to keep the mounts acid-free, and for that purpose all 

 reagents except the destaining fluid were made slightly alkaline with dessicated 



