Development of the foetal membranes in the Indian leaf-nosed bat, Hipposideros bicolor pallidus.

Abstract

Some stages of the development of the foetal membrane of Hipposideros bicolor pallidus have been described. During early stages the yolk sac establishes contact with the uterine wall on all the sides except where the embryo intervenes between it and the uterine wall. However, the chorio-vitelline placenta develops only on the lateral sides of the uterus because the splanchnopleure of the yolk sac is separated from the chorion before the abembryonic segment of the yolk sac becomes vascularized. During later stages of development the yolk sac undergoes collapse, its cells hypertrophy, and it ultimately comes to lie as a shrunken gland-like structure adjacent to the placenta. The allantois has a large endodermal vesicle up to about mid-pregnancy, but it becomes reduced to a small rudiment during the final stages. There is a distinct allantoic duct until term. The allantoic placenta is cup-shaped during earlier stages and has a narrow cleft in the center of the base of the cup. As development proceeds this cleft becomes wider and deeper so that the placenta ultimately becomes doublediscoidal and is located on the mesometrial side of the uterus. The finer morphology of the placenta is labyrinthine and endotheliochorial.