The fine structure of the placenta and chorionic vesicles of the bush baby, Galago crassicaudata.

The fine structure of the placental villi and the chorionic vesicles of the bush baby, Galago crassicaudata, were examined. The placenta was of the diffuse epitheliochorial type. The trophoblastic epithelium of the placental villi consisted of cells joined by tight junctions and desmosomes. The apical borders of these cells interdigitated with corresponding processes on the uterine epithelial cells. The fetal capillaries indented the trophoblastic cells later in gestation, and the trophoblast over the capillaries was correspondingly thinner with advancing gestation. The trophoblast of the villi was characterized by numerous lipid droplets and moderate amounts of granular endoplasmic reticulum (ER). The apical cytoplasm often had many mitochondria as well as small electron-dense vesicles and tubules. Uterine epithelial cells contained agranular ER and a well-developed Golgi apparatus. The apical cytoplasm contained numerous granules often with an electron-dense content. The uterine epithelial cells appeared to be secretory, contributing to the electron-dense material found between the fetal and maternal cells. Fetal capillaries were of the continuous type, whereas occasional fenestrae were observed in maternal capillaries. Recesses in the trophoblastic epithelium occurred at the tips, sides, and bases of the villi. These areas had taller trophoblastic cells that appeared to be more active in phagocytosing uterine content. The chorionic vesicles are invaginations of the chorion opposite the mouths of uterine glands. A layer of columnar trophoblastic cells covered the villi of the vesicles. These cells had abundant vacuoles and coated pits and vesicles. The mesodermal component of the chorionic vesicles included a capillary network and a layer of smooth muscle cells in the wall of the vesicle. It was concluded that the trophoblast of the placental villi is engaged in both hemotrophic and histotrophic nourishment of the embryo. The specialized chorionic vesicles are particularly important in providing histotrophic nutrients to the embryo, especially the secretions of the uterine glands. The similarity of the chorionic vesicles to the areolae of other species suggests they may be the pathway by which iron is transported from mother to fetus, perhaps by receptor-mediated endocytosis of macromolecules derived from uterine gland secretions.