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ENDOMETRIAL DIFFERENTIATION IN THE PREGNANT SOW AND THE NECROTIC TIPS OF THE ALLANTOCHORION

Hughes (1927) suggested that the degenerate extremities of the pig's allantochorion, the necrotic tips, may discourage the formation of vascular anastomoses between one conceptus and its neighbours and may be important in controlling the incidence of freemartinism in the pig. The gross appearance of the allantochorionic extremities has been described from 39 days' gestation onward (Ashdown & Marrable, 1967) and histologically the necrotic tip has been shown to be an envelope of closely packed collagenous lamellae lacking both trophoblast and allantoic endoderm (Marrable, 1968). The endometrium adjacent to the necrotic tips is very pale, covered with mucus (Lesbre, 1910), contains numerous lymphocytes and plasma cells (Marrable, 1968) and has an epithelium which is rich in glycogen (Lovell & Garm, 1965). The present observations concern the earlier development of the necrotic tips, the associated zones