|Title||Postharmostomum helicis (Leidy, 1847) Robinson 1949, (Trematoda), its life history and a revision of the subfamily Brachylaeminae|
|Year of Publication||1950|
|Degree||Doctor of Philosophy|
|Number of Pages||150 pp.|
|University||University of Michigan|
|City||Ann Arbor, MI|
Trematodes belonging to the family Brachylaemidae have attracted the attention of investigators for more than a century. Early workers, limiting their studies to adult and metacercarial, placed little or no emphasis on sporocyst or cercarial stages. Not only have complete life history studies been few, but the taxonomy of the group, because of this conspicuous lack of information regarding early developmental stages, has suffered accordingly. When, in 1946, a survey of terrestrial snails in the vicinity of Ann Arbor, Michigan revealed a remarkably high percentage of infestation with brachylaemid metacercariae, my interest was sufficiently aroused to undertake the study of a life cycle with particular emphasis on those developmental stages hertofore largely neglected. The abundance of Anguispira alternata, one of the most commonly found terretrial molluscs in this area, from which large numbers of metacercariae could be recovered, aided greatly in the completion of the life cycle in the laboratory. The comparative ease in the maintenance of laboratory-reared snails helped to make available for study cercariae and sporocysts in all stages of development. Particular attention has been given to the development of the sporocyst generations. Evidence has been secured concerning the production of both mother and daughter sporocysts, thus giving further confirmation to the the generally accepted view that cercariae are produced by a second generation of so-called parthenitae. The new facts are contrary to the commonly-held view of many investigators that cercariae in Brachylaeminae are produced directly by the first-generation sporocyst.