[Fine structure of the septum in twin pregnancy]

The structure of the septum in bigeminal pregnancy was examined via the electron microscope after normal pregnancy. The cellular junctions were desmosomes and "gap junctions" in the amnionic epithelium, whereas in the chorionic epithelium "gap junctions" and "tight junctions" were found occasionally besides desmosomes. The basement membrane was multilayered and discontinuous both in the amnion and in the chorion. Since, physiologically, the desmosomes and the gap junctions cannot be regarded as a diffusion barrier against proteins, and since the rare tight junctions are without any significance for the passage of the proteins through the septum, and, furthermore, since a discontinuous basement membrane cannot exercise any action in the nature of a barrier, these structural peculiarities of the septum seem to indicate that the intercellular spaces and the discontinuous basement membrane of the amnion and of the chorion in the septum may represent a paracellular path for the passage of the proteins between the two amniotic cavities.