Gametogenesis, Egg-Capsule Formation, and Early Miracidial Development in the Digenetic Trematode Halipegus eccentricus Thomas

Abstract

Observations on H. eccentricus showed that 3 spermatogonial divisions and 2 meiotic divisions result in the formation of 32 spermatids which in turn differentiate into elongate sperms with nuclear heads and cytoplasmic tails, and a residual cytoplasmic mass. Oocytes at the periphery of the ovary have early synaptic stages while those in the center show large nuclei with diffuse chromatin; they retain this appearance until after sperm penetration and encapsulation. Globules of shell material from vitelline cells form an unstratified capsule around the oocyte and vitelline cells in the ootype. Meiotic divisions of the oocytes occur in the uterus. Eleven bivalents were found in spermatocytes and oocytes and 22 chromosomes in zygotes. Glycogen was present in fully developed vitelline cells and sperms. Early differentiation of 2 vitelline membrane cells, epidermal and subepidermal cells, and gland primordia occurs in the development of the miracidium.