Plate 15

Copyright © 1995
to the
"Frontiers in Bioscience"

Onset of Gastrulation

Radial intercalation has led to a thinning out of the blastocoel roof, which now consists of two layers: the outer, epithelial layer and the inner, sensorial layer. The expansion of the blastocoel roof by epibolic movement is more advanced on the dorsal side, where animal material is con-stantly shifted vegetally (arrow'). Bottle cells have formed at the blastopore and have begun to move inwards. The subepithelial suprablastopor-al cells involute internally and move animal-wards. The cells of the deep zone move animal-wards, approaching the blastocoel roof (arrow'). These processes have not yet begun on the ven-tral side. The boundary between NTMZ and IMZ is not easy to locate; the drawing indicates this border only approximately. (Staining: BCB)