1. The life cycle of Gigantobilharzia huronensis Najim, 1950, was determined experimentally. The snail, Physa gyrina (Say), served as the intermediate host. The natural definitive hosts were goldfinches (Spinus tristis tristis) and the cardinals (Richmondena cardinalis). Chicks and canaries served as susceptible hosts in the laboratory2. The shortest time recorded for the hatching of eggs in water is about 20 min. Cercariae were liberated from the snail as early as 24 days after exposure. Eggs were found in the faeces of the definitive host 31 days after the first exposure to the cercariae.3. Adult worms are elongate and filiform. Females are longer than males, and in both sexes the oral and ventral suckers are absent. The cuticle has no spines. A short gynaecophoric canal is present. Up to 300 testes are present in the male and the cirrus is spiny. Laurer's canal is present and vitelline follicles fill most of the body of the female. Eggs are spherical to very broadly ovoid in shape and averaged 93µ in length by 88µ in width. The uterus contains from one to several eggs at a time, and the genital pore is located shortly posterior to the mouth opening.4. The miracidium has a peculiar wide gap between the second and third rows of epidermal plates. The body covering consists of twenty-two epidermal plates arranged in four rows of 6:9:4:3. The mother sporocyst has an elongate, sac-like body. A birth pore is present in the mature mother sporocysts. The daughter sporocyst also has an elongate body, but the anterior end is covered with spines. A birth pore is present in the mature daughter sporocysts.5. The cercaria is an apharyngeal, furcocercous, brevifurcate, distome with pigmented eyespots; the body averaging 240µ in length by 72·5µ in width; the tail stem averaging 268·5µ in length by 30µ, in width; the furca averaging 146·8µ in length by 15µ in width. The furcae have fin folds. The body and tail are covered with spines. There are five pairs of penetration glands and an oral gland. The excretory system is usually 2[(2) + (2+1)]. The cercaria attaches to the surface film of the water with the body parallel to it and the tail hanging downward at different angles. The cercaria is a dermatitis producer in human skin.
