Printed in Great Britain CIRCUS MOVEMENTS AND BLEBBING LOCOMOTION IN DISSOCIATED EMBRYONIC CELLS OF AN AMPHIBIAN,

Circus movements, which involve the circumferential rotation of a hyaline cytoplasmic protrusion, occur in cells obtained by EDTA dissociation of gastrula-atage Xenopus laevis embryos. Only a few dissociated blastula-stage cells show circus movements, more early gas-trula-stage cells show them, and nearly all late gastrula-stage cells show them. Circus movements cease in cells prior to mitosis and begin again in daughter cells after mitosis is completed. In early gastmlae, only 17 % of prospective endodermal cells show circus movements while 7 9 % of prospective mesodern, archenteric roof, and posterior neural ectoderm do so. Isolated cells as well as groups of cells in vitro are often propelled by circus movements. There is an obvious antagonism between cell contact and circus movements. The morphogenetic significance of circus movements and blebbing locomotion is discussed