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The cell movements and contacts in somite formation in Xenopus are unusual. The vertebrate somite as seen in section is traditionally described as a rosette and is formed by pinching off a group of cells from the paraxial meso-derm; these cells then increase intercellular contacts. Typical rosettes with cells radiating from the myocoel may be seen in the Axolotl (Fig. 1 A). Not all the cells of a rosette have the same fate. The lateral ones become dermis and spread out under the epidermis forming a continuous sheet with their counterparts from neighbouring somites. The majority of the somitic cells, which are myo-tomal, will elongate antero-posteriorly and fuse end to end with other cells of the same somite (Przybylski & Blumberg, 1966; Riabova, 1966). In this way myo-tubes are formed which stretch from one end of the somite to the other and obliterate the myocoel. Somites are formed in an orderly anterior-posterior succession. In a pre-hatching Xenopus larva of stage 28 (Nieuwkoop & Faber, 1956) it can be observed that the myotomal cells are already elongated antero-posteriorl