Abstract

CASTANOS, Melody et al. Histology of extraembryonic membranes during extended egg retention in Sceloporus aeneus (Squamata: Phrynosomatidae). Acta Zool. Mex [online]. 2009, vol.25, n.2, pp.303-314. ISSN 2448-8445.

Morphology of extraembryonic membranes in the lizard Sceloporus aeneus was described from the modal time of oviposition (30-31) to advanced stages of retention (37) using light microscopy. At the normal stage of oviposition the choriovitelline membrane is present as in other oviparous species, moreover is replaced by the chorioallantoic membrane. At stages 34-37, the allantoic membrane extend beyond the equator of the egg where it contacts the bilaminar onphalopleure. Only in two specimens of stages 34 and 35, this membrane fully encircles the yolk sac. During egg retention, a regionally diversified chorioallantoic membrane was observed, having a thin squamous chorionic epithelia enveloping the embryonic hemisphere, and a cubic or cylindrical epithelia covering the abembryonic one. The bilaminar onphalopleure showed a cubic and cylindrical epithelia in the most advanced embryonic stages (35-37). We suggest that the chorioallantoic membrane plays a role in calcium and water transport towards the embryo, the later not causing any increase in volume of the egg inside the uterus. The persistence of the bilaminar onphalopleure in advanced stages of development may accomplish the same function of water and calcium transport during the interval of uterine egg retention, as it occurs in extraembryonic membranes of viviparous species within Reptilia.

Keywords : Histology; extraembryonic membranes; intrauterine egg retention; Sceloporus aeneus; viviparity.

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