ULTRASTRUCTURE OF PLACENTAL LABYRINTH IN KANGAROO RAT DIPODOMYS

Representative pieces of labyrinth of near‐term chorioallantoic placentas from three species of Dipodomys and one species of Microdipodops were fixed in glutaraldehyde and osmium tetroxide and examined with the electron microscope. The barrier separating the fetal and maternal blood streams in the labyrinth was found to consist of (1) the fetal endothelium and its associated basal lamina (basement membrane), (2) a single layer of trophoblast which is cellular rather than syncytial, and (3) the maternal endothelium and its associated basal lamina. Thus the chorioallantoic placenta appears to be of the endotheliochorial type in these rodents rather than hemochorial or hemoendothelial as previously suggested. Copyright © 1969 Wiley‐Liss, Inc.