The role of the cellular envelope in the morphogenetic movements of teleost embryos

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Abstract
Nile blue sulfate solutions can be applied to teleost blastoderms in dosages sufficient to stain only the cellular envelope, or to penetrate uniformly from the surface to desired depths among the interior cells. Surface cells, if overstained, break loose from the cellular envelope and migrate to the interior, with subsequent failure of epiboly and differentiation. Less dosage slows down epiboly but does not disrupt organogenesis. The cellular envelope does not contribute any substantial number of cells to the terminal node or any at all to the inner germ ring. The hypoblast is not invaginated from it, nor does it contribute to the notochord, the mesoderm, or the endoderm sheet. Its fate is exclusively epidermal, and it is at all times separable from the inner blastomeres and embryonic tissues. Previously published “fate maps” of the teleost blastodisc must be understood as relating to the internal cells, not the cellular envelope. No conclusive evidence yet exists that the morphogenetic movements of teleosts include either an invagination or an inturning movement, at or inside the blastodisc rim.

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