Abstract
The California gull Larus californicus, has been reported as a host for Diphyllobothrium cordiceps from cutthroat trout, Salmo clarki, (Post, 1971) . A comparison of development and of morphological forms of D. cordiceps in young gulls and hamsters which had previously been proven to be susceptible to infection was considered desirable. Previous experimental exposures of cutthroat trout and grayling, Thymallus arcticus, to plerocercoids naturally infected from cutthroat trout had given mixed results with transfer of plerocercoids from cutthroat to cutthroat but not from cutthroat to grayling (Kingston et al., 1980) though grayling have been cited as a natural host for the tapeworm (Post, 1971). Work in 1980 was directed towards the elucidation of these aspects of the life cycle of D. cordiceps.