InChaerephon plicata the definitive amnion is formed by the development of folds. The yolk-sac splanchnopleure undergoes progressive collapse and folding until it ultimately remains as a free gland-like structure with hypertrophied endodermal and mesodermal cells. It acts as an active haemophagous organ after limb-bud stage. An extensive chorio-vitelline placenta, which is formed during early gestation is progressively abolished and replaced by the chorio-allantoic placenta. Two kinds of chorio-allantoic placenta are formed—a diffuse endotheliochorial placenta, which persists until about midpregnancy, and a definitive discoid placenta which is mesometrically located, labyrinthine and haemomonochorial.