Kupffer's vesicle in Fundulus heteroclitus: a scanning and transmission electron microscope study.

Kupffer's vesicle, a transitory organ peculiar to teleost embryos, was investigated in embryos of Fundulus heteroclitus by scanning electron microscopy. The roof of the vesicle is constructed to rather large columnar cells which are in continuity wiht hypoblast cells. Each of the roof cells is adorned with a single long cilium which emerges from a depression in the center of the surface and extends into the cavity of the vesicle. Studies with a transmission electron microscope confirm and extent these observations. The surface of the roof of the vesicle variously exhibits the presence of droplets and viscous and/or filamentous material. The exposed surface, however, sometimes appears clean and somtimes appears to have undergon partial destruction. The periblast floor of the vesicle is characterized by the presence of numerous folds and/or microvillus projections into the cavity of the vesicle. A filamentous precipitate is sometimes present. These observations are discussed in terms of the possible functional significance of this unique evanescent organ of the teleost embryo.