Further observations on the fine structure of the development of the interrenal tissue of the chick embryo

Abstract

The interrenal tissue of 8-21 day-old White Leghorn chick embryos and of 1 day-old chicks was studied by means of electron microscope. The interrenal cells in 8-10 day-old embryo are characterized by the presence of numerous free ribosomes, very small amount of endoplasmic reticulum, oval or club-shaped mitochondria with lamellar cristae and of a few small lipid droplets. The fine structural signs for steroid secretion, such as round or oval mitochondria with tubular cristae and smooth endoplasmic reticulum begin to appear in 11-13 day-old embryo, and the interrenal cell of the 16 day-old embryo shows typical morphological characteristics for the steroid-secreting cell. After 16 days, the cytoorganelles of the interrenal cell do not show any qualitative changes. These facts may indicate that the interrenal cell of the domestic fowl is functionally differentiated around 11 days of incubation at latest. The interrenal tissue of 8-9 day-old embryos somewhat resembles a tubular gland, though the zonula occludens is not present. In addition, the interrenal cell shows an incomplete cell polarity, throughout the embryonic days examined. These findings indicate that the interrenal cell of the embryonic domestic fowl, which is derived from a mesothelium, remains slightly an epithelial nature.