The culture of Diplostomum spathaceum metacercariae on the chick chorioallantois.

Metacercariae (2,828) obtained from the lens of naturally infected Aplodinotus grunniens were transplanted onto chorioallantoic membranes (CAM's) of 94 eggs (means 30/egg) 5 to 12 days old. Membranes were examined 2 to 8 days later and 381 flukes were recovered. Two hundred fifty-nine chorioallantoic-grown worms were transferred to 28 additional embryos 3 to 8 days after the initial inoculation. These eggs were examined 3 to 11 days later. Fifty-three serially transferred worms were recovered after 7 to 14 days on CAM's. Six stages of development were recognized: stage 1, immature; stage 2, genital rudiment; stage 3, testes; stage 4, follicular ovary; stage 5, vitellaria; stage 6, ovigerous. The intestinal ceca of many worms (except stage 1) contained ingested blood. Trematode eggs oviposited on CAM's were embryonated in tap water, and viable miracidia were observed in 15. No previous study has achieved gonadal development in Diplostomum spathaceum on the CAM. Furthermore, inasmuch as metacercaria matured and produced fertile eggs, this form is shown to be a useful model for the study of trematode differentiation. The development of metacercariae to ovigerous adults capable of producing viable miracidia suggests that the CAM shares characteristics with the intestine of the definitive host, a piscivorous bird.