Thesis (Ph. D.)--University of Michigan, 1928. / Reprinted from Transactions of the American Microscopical Society, vol. XLVIII, no. 3, July, 1929, vol. XLIX, no. 1, January, 1930 and vol. L, no. 3, July, 1931. Includes bibliographical references.

The family Bucephalidae is unique in the class Trematoda by virtue of the mouth being situated near the mid-ventral portion of the body. Other characteristics of the family include: haptor near the anterior extremity; a simple, sac-like gut with pharynx and esophagus; genital pore ventral, just anterior to the posterior extremity; gonads posterior and vitellaria species live in the gut of marine and fresh-water fishes. The metacercariae are found encysted beneath the skin or in the nervous system of other fishes serving as second intermediate hosts. Sporocysts and cercariae have been recovered from a variety of lamellibranchs. A generalized life cycle of the bucephalids can be stated as follows: eggs discharged from the intestine of the definitive host produce free swimming miracidia which enter the mantle cavity of a lamellibranch; branching sporocysts develop within the gonads and, allegedly, other organs (although the writer observed them only in the gonads); cercariae are produced directly in the sporocysts or daughter sporocysts, and when mature are discharged through the excurrent siphon of the host. Woodhead (1931) described rediae in the sporocysts of Bucephalus elegans and Rhipidocotyle papillosum although Knickern (1950) and Ciorda (1956), working with Rhipidocotyle septpapillata and Rhipidocotyle papillosum respectively, failed to note a redial stage. The writer, too, has seen no rediae. The cercariae, when coming in contact with an appropriate fish, attach to it by means of long, filamentous tall appendages and finally bore into a suitable site for encystment, losing their tails on the way (Woodhead, 1927). The metacercariae reach the definitive host when the smaller fish is devoured. It is not uncommon for the same species of fish to act as both second intermediate and definitive hosts.