The fine structure of the placenta of the blue shark, Prionace glauca.

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The fine structure of the placenta of the blue shark, <I>Prionace glauca</I>, was observed.The placenta was divided into distal and proximal portions.In the distal portion, an egg-capsule was not present, and maternal and fetal epithelia lay side by side.In the distal portion, the maternal epithelial cells contained many granules, lipid droplets, mitochondria, and developed RER and Golgi complexes.Fetal epithelial cells were covered with microvilli and possessed many small tubular structures and coated vesicles in the apical region.The space between maternal and fetal epithelia was filled with high electron dense and PAS-positive materials which seemed to be derived from maternal epithelium.In the proximal portion, the epithelium was characterized by expanded intracellular spaces.Many mitochondria were scattered in the basolateral portion of epithelial cells.From these morphological observations, it is thought that the fetus obtains its nutrients including macromolecular materials through the placental tissue and through the exchange of water-solute and gases between the uterine fluid and the epithelium of the proximal portion of the placenta or the gill, at least at full-term.Ovoid cells which seemed to be macrophage cells were observed in the intracellular spaces of the fetal placenta.
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