SURFACE CONTRACTION AND EXPANSION WAVES CORRELATED WITH DIFFERENTIATION IN AXOLOTL EMBRYOS .2. IN CONTRAST TO URODELES, THE ANURAN XENOPUS-LAEVIS DOES NOT SHOW FURROWING SURFACE CONTRACTION WAVES

We have observed a number of contraction waves traversing the axolotl (Ambystoma mexicanum) embryo (a urodelan amphibian) from the midblastu la transition up to at least neural tube closure, and wished to learn if similar ''differentiation waves'' appear on the popular laboratory anuran amphibian, the South African clawed toad, Xenopus laevis. Time lapse video microscopy showed that no contraction waves are visible on the surface of Xenopus from gastrulation through neurulation. It is p ossible that cell intercalations in the double-layered ectoderm of the Xenopus embryo are homologous to the surface waves in the single laye red ectoderm of the axolotl embryo. In any case, a simple, universal c orrespondence between surface waves and induction phenomena and differ entiation does not exist.