The blastomere periphery ofXenopus laevis, with special reference to intercellular relationships.

The peripheral region of theXenopus laevis blastomere is considered to be comprised of the extracellular material, the plasma membrane and the subsurface cytoplasm. These regions were examined with the electron microscope during cleavage and blastula stages (stages one to seven, Nieuwkoop and Faber, 1967). The cell contact relationships varied according to the location of the cell in the embryo. Superficially, a dense terminal junction occurred, possessing point contacts where the membranes approached to within 30 Å. More deeply, a variety of relationships appeared: wide intercellular spaces bridged by pseudopodia, long regions of unbridged parallel membrane or complex interdigitation. Tight junctions were found in limited numbers and developed at about stage seven. Extracellular material was examined using histochemical techniques on dissociated andin situ cells. The latter had appreciable amounts of such material, but dissociated cells reacted inconsistently to different techniques. The cytoplasm subjacent to the membrane possessed a filamentous network at all stages examined, but extensive microfilament tracts and microtubules appeared only at gastrulation.