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Morphogenetic Movements and Fate Maps of Vertebrates

WILLIAM W. BALLARD
DOI: http://dx.doi.org/10.1093/icb/21.2.391 391-399 First published online: 1 May 1981

Abstract

SYNOPSIS. Fate maps are totally lacking for hagfishes, rays, holocephals, dipnoi, holostei and mammals, and for all except two of the thirty or so orders of the huge teleost assemblage. Important errors have been found in earlier studies of the movements by closer control of marking techniques, but there are still major elements in the literature that remain unconfirmed. Recent studies on Salmo, Xenopus and chick suggest that a wider sampling of major vertebrate groups will uncover more unsuspected variations in this phase of embryology. Experimental results on the chondrostean sturgeon Acipenser are here compared and contrasted with those on Salmo and Xenopus. Though chondrostei and teleosts had a relatively recent common ancestry, the morphogenetic movements and fate map of Acipenser give no hint as to how the uniquely teleostean behavior could have arisen. Instead the experiments have shown in new elaborate detail how close the early development of Acipenser is to that of modern amphibia, closer to Xenopus than to Rana, closer to anura than to urodeles. The search for unity in the field of comparative morphogenetic movements is plagued by lack of breadth in the sample of vertebrates hitherto studied but also by a vocabulary too much loaded with ancient homological thinking. It is pointed out that when a group of movements, all called invagination—or all called epiboly, is studied closely it can be discovered that they may be doing quite different things, controlled by different environmental factors. General theory of this part of embryology requires the bringing together of the knowledge of cellular movements from in vitro and non-embryonic systems with the knowledge of the full variety of normal patterns of morphogenetic movements in the vertebrates. Before this can be accomplished, we will need a precise knowledge of what the cells are actually doing in all the sectors of these patterned movements, and in all the major patterns that the phylum has produced.

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