Monometacercarial infections of the trematode, Leucochloridiomorpha constantiae, in the bursa of Fabricius of the domestic chick produce adults capable of self-insemination and eggs containing miracidia. Observations on worm pairing, cross-copulation, and the absence of autocopulation suggest cross-insemination as the prevalent mode of reproduction in double-worm infections. Eggs containing miracidia were first seen in flukes from 7-day-old doubleand 9-day-old single-infections and the number of such eggs was markedly reduced in the latter. Experiments reviewed by Bacha (1966), Nollen (1968), and Fan and Chiang (1970) indicate that certain species of hermaphroditic digenetic trematodes are capable of producing eggs containing miracidia in situations that preclude cross-insemination, presumably by self-fertilization or parthenogenesis. Using autoradiographic techniques Nollen (1968) demonstrated that although Philophthalmus megalurus adults are capable of self-insemination, the usual mode of reproduction is cross-insemination when more than one worm is present. The purpose of this study was to determine if Leucochloridiomorpha constantiae adults are capable of self-insemination and the production of eggs containing miracidia in situations that preclude cross-insemination, and to examine reproduction in flukes permitted to cross-inseminate. Results of observations on reproduction in singleand double-worm infections of L. constantiae in the domestic chick are presented herein. MATERIALS AND METHODS Metacercariae were dissected from uteri of naturally infected Campeloma decisum snails (Mueller, 1935; Allison, 1943) collected in Jenning's Lake, Camden County, New Jersey. Fresh larvae or those stored for up to 2 days in Ringer's at 10 C with no apparent decrease in viability were used. The cloacal drop method of Allison (1943) was used to expose 121 1to 2-day-old domestic chicks Received for publication 9 February 1971. * Supported in part by a research grant from The Lafayette College Committee on Advanced Study and Research. t Present address: Institute for Pathobiology, Lehigh University, Bethlehem, Pennsylvania 18015. anesthetized with Equi-Thesin (Fried and Berry, 1961) to either 1 or 2 metacercariae per chick (Tables I, II). Chicks were necropsied 7 to 10 days postexposure and the bursa of Fabricius was removed and inverted in Ringer's. Following in situ observations each worm was examined live under light coverslip pressure within 1 to 2 min of its removal. To assess development, each worm's uterus was teased in 1 to 2 ml of Ringer's and 100 to 200 eggs per worm examined at random. Fully developed eggs, i.e., those containing a pear-shaped miracidium (Allison, 1943) were scored and tabulated in percentage per worm (Tables I, II).