Ultrastructural observations on the chorioallantoic placenta of the golden-rumped elephant shrew, Rhynchocyon chrysopygus

Abstract

The chorioallantoic placenta of the elephant shrew (Rhynchocyon) was studied at the ultrastructural level. The placenta is haemonochorial with an appparent lack of microvilli on the syncytiotrophoblastic surface. There is, however, an unusual development of subsurface bays which are covered only by an ectoplasmic layer of trophoblast. The contents of the bays is PAS-negative and is similar in both texture and appearance to the maternal blood plasma. The basal trophoblastic cells are exceptionally tall and are held together by numerous desmosomes. Their basal lamina, which is on the trophospongial side, it unusually thick. At the fetomaternal junction the basal trophoblastic cells are coated with a finely granular electron-dense precipitate of unknown nature.

Electron-dense particles resembling iron deposits are demonstrable in the fetal mesenchyme of the labyrinthine zone.