STRUCTURE OF INTRA-CHORIONIC BLOOD SINUS IN CHICK-EMBRYO

Abstract

An EM study of portions of the chorio-allantoic membranes from 15 day old chick embryos was conducted. Only sections made parallel to the surface of the membrane were used. The analysis of both 1 .mu.m thick sections stained with toluidine blue and of thin sections stained with uranyl acetate and lead citrate, showed that the lumen of the intraepithelial vascular spaces in the chorion constitutes a single cavity extending over the whole membrane. The vascular arrangement is a single blood sinus and not a network of capillaries or sinusoids. The large lumen of the sinus is interrupted by cylindrical columns. Each column is enveloped in a layer of endothelium, a basal layer intervening. The core of the column is formed by cytoplasm from 2-5 different cells (villus-cavity cells, capillary-covering cells or various combinations of both).