Observations on the Development of the Miracidium and the Germ Cell Cycle in Heronimus chelydrae MacCallum (Trematoda)

Abstract

Development of the somatic tissues and germinal cells of the miracidium, and a tracing of the germ cell cycle from the 2-cell stage of the miracidium to the genital primordium of the cercaria were studied in the lung fluke of turtles. Most somatic tissues of the miracidium were found to be derived indirectly from the ectodermal cell, while germinal cells were found to be derived indirectly from the propagatory cell of the 2-cell miracidial embryo. After penetration of snail hosts of the genus Physa, miracidia develop into mother-sporocysts. Germinal cells within the miracidium-mother sporocyst divide by mitosis and develop directly into cercarial embryos. No meiotic divisions or fertilization stages were observed in the miracidium-mother sporocyst.