Histology of abortive egg sites in the uterus of a viviparous, placentotrophic lizard, the skink Chalcides chalcides

Although abortive uterine eggs are often assumed to be resorbed by females of the viviparous skink Chalcides chalcides , little microscopic evidence of resorption of such eggs is available. Oviducts from pregnant female C. chalcides in which egg resorption was inferred were examined histologically to seek a morphological basis for resorption. Uterine histology at the site of abortive eggs was very similar to that of lizards in early pregnancy. The uterine epithelium consisted of a monolayer of pseudostratifed columnar cells that showed no evidence of yolk phagocytosis. The uterine lamina propria exhibited shell glands and modest vascularity, typical of early gestation, and contained neither yolk droplets nor accumulating leukocytes. Unattenuated regions of the lamina propria contained occasional macrophages and mast cells, some of the latter of which were undergoing degranulation. The abortive eggs often were collapsed with ruptured shell membranes, and some were undergoing extrusion from the incubation chambers down the oviduct. In eggs that had begun developing, extraembryonic ectoderm and endoderm were atypical in location, and had failed to enclose yolk leaking from the eggs. Oviducts sampled from later in the reproductive season were reproductively inactive, and showed no trace of abortive eggs or egg components. We postulate that abortive eggs are extruded from the oviduct by pregnant females under conditions of physiological stress, as a means of enhancing future reproductive effort. J. Morphol. 235: 97–108, 1998. © 1998 Wiley‐Liss, Inc.