According to the work of Rausch (1953) , two species of helminth parasites, Porrocaecum decipiens (Krabbe, 1878) and Microphallus pirum (Afanas'ev, 1941), are pathogenic for the sea otter, Enhydra lutris (L.) , on the Aleutian Island of Amchitka. In continuation of investigations of sea otter mortality on Amchitka during the latter part of May and early June, 1952, the writer made an attempt to
obtain information on the life cycles and developmental characteristics of these parasites. It is the purpose of this paper to report the results of these observations.