Development and placentation of the Indian fruit bat. Pteropus giganteus giganteus (Brünnich).

SUMMARY. The uterus is bicornuate and the two horns of the uterus apparently united are separate for the greater part. Pregnancy occurs only in one horn. The ovary of both sides produces ova but the corpus luteum is present in the ovary of the pregnant side. Copulation takes place early in September and parturition in late January or early February. The embryonic mass is at first lateral but later mesometrial. There is an implantation cavity formed within a protruding mass of nterine endometrium. The implantation is partly interstitial. The trophoblast cells penetrate the uterine endometrium very early in development. The amnion is formed by eavitation. The yolk‐sae is on the antimesometrial side and the allantoic vesicle on the mesometrial side. The bilaminar omphalopleure becomes trilaminar by growth into it of mesoderm cells at the prochordal plate stage. The yolk‐sac placenta is formed at this stage. The primitive trophoblast forms the syneytiotrophoblast by proliferation. It erodes the uterine mucosa, forming in later stages a syneytial shell and later replaces the whole of the protruding uterine endometrium. The basal trophoblast cells form the cytotrophoblastic cords. The wall of the allantoic vesicle provides the vascular mesenhyme tissue. The allanto‐chorionic placenta is formed on the mesometrial side and consists of syncytiotrophoblast, cytotrophoblastic cords and allantoic vascular mesenchyme and large blood spaces containing maternal blood. In early stages, maternal endometrial cells are present but these are lost later. There is no “inversion”. At mid term, the allantoic vesicle extends laterally and sends out villous mesenchymal projections. At the same time, the yolk‐sac wall is withdrawn and is thrown into folds which lie first laterally and later on the mesometrial side. The yolk‐sac forms a gland and persists up to parturition. The foetal blood cells are nucleated up to at least a month prior to parturition. The entire endometrium which protrudes into the uterine lumen is converted into a placenta. On the mesometrial side it is attached to the uterine myometrium by a narrow stalk. Large, round decidual cells are present in this region. The placenta is at first horse‐shoe shaped. Later the loops contract; the middle portion thickens and finally it assumes the form of a dise on the mesometrial side. There is no decidua capsularis. The cytotrophoblastic cords become thin and elongated; they branch and anastomose. The placenta is mesometrial, discoidal, labyrinthine and haemochorial.