Light and electron microscopic studies of the morphological features of immature and mature rodlet cells in Catostomus commersoni are presented emphasizing the cells' association with epithelial tissues. The peripheral fibrillar layer is lacking from the apex and from the base of the cell. A cytoplasmic extension from the base may be a feeding mechanism whereby the rodlet cell obtains nutrient at the expense of adjacent cells leaving intercellular spaces often containing myelin figures. RNAase digestion studies demonstrate the presence of RNA in the electron dense rodlet core.The structure and histochemistry of the rodlets which do not appear to disintegrate upon expulsion from the cell are compared to the cytoplasmic inclusions of both normal fish cells and protozoan parasites. The possible association of the rodlet cell with various pathological conditions is briefly reviewed and the authors conclude that it is premature to disregard the possibility that this cell could be a parasite or infective agent.

The life cycle of the brachylaemid trematode Scaphiostomum pancreaticum McIntosh, 1934, was completed experimentally in the laboratory. Eggs were obtained from trematodes removed from naturally infected Tamias striatus. Eggs are mature when laid and hatch naturally only after ingestion by a snail. In vitro hatching and subsequent examination of the miracidium was accomplished in snail gastric juice. Sporocysts developed in Anguispira alternata and cercarial emergence began 129 days after infection. Metacercariae developed in the kidney of A. alternata, Triodopsis albolabris, and Haplotrema concavum and were infective to the chipmunk after 5 months, and ovigerous adults were obtained in 30 days. This is the first description of the life cycle of a member of this genus.

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Four species of trematodes of the family Eucotylidae were collected from birds in British Columbia. Eucotyle castanea n.sp. from Melanitta deglandi (Bonaparte) differs from other members of the genus mainly by the presence, throughout its parenchyma, of a reddish-brown pigment. E. cohni Skrjabin, 1924 was recovered from Podiceps grisegena holböllii Reinhardt, Clangula hyemalis (Linnaeus), Bucephala clanguia (Linneaus), and Padiceps aurittis (Linnaeus). E. warreni Schell, 1967 was collected from Bucephala islandica (Gmelin) and Tanaisia fedtschenkoi Skrjabin, 1924 from Charadrius vociferus Linnaeus. This is the first record of the occurrence of these parasite species in Canada.The structure of the cirrus sac in E. castanea and E. cohni and the excretory system of the latter species are described. The relationship between Eucotyle and Tanaisia is discussed and a key to the species of Eucotyle is included.

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