Ultrastructural studies of the placenta of the ewe: phagocytosis of erythrocytes by the chorionic epithelium at the central depression of the cotyledon.

Extravasated maternal blood, which escapes from capillaries and larger blood vessels within the tips of the maternal septa, is responsible for the characteristic pigmentation of the central depression of the ovine cotyledon in the last third of pregnancy. The chorionic epithelium of this region is actively engaged in the uptake and subsequent breakdown of maternal erythrocytes, which may represent an important source of iron for the foetus during the period of maximum intra-uterine growth.