par Brachet, Jean 
Référence Current Topics in Developmental Biology, 11, page (133-186)
Publication Publié, 1977
Référence Current Topics in Developmental Biology, 11, page (133-186)
Publication Publié, 1977
Article révisé par les pairs
| Résumé : | This chapter focuses on the gray crescent of the amphibian eggs. The gray crescent is a “germinal localization” and it is a marker of the dorsal side of the fertilized egg, the future embryo, and the adult. Thus, in the fertilized egg, it is already possible to see, by simple observation with a lens, all the major coordinates of the future adult; the animal pole becomes the head, the vegetal pole the gonads, the gray crescent containing half the dorsal side, with nervous system and notochord, and the opposite side becomes the ventral. The gray crescent is a very useful morphological marker, visible in certain favorable amphibian species, for the prospective dorsal side of the embryo and the adult; the plane that cuts it into two equal halves is the plane of bilateral symmetry that is retained by the adult. Eggs that, for some reason, have not acquired a dorsoventral organization, and have thus neither a visible nor a cryptic gray crescent, develop into anidian embryos, such anidians are occasionally found among frog eggs that have been artificially fertilized and, more frequently, among the xenopus eggs, where the gray crescent has been injured; they remain like ciliated spheres that whirl around at great speed and finally die, perhaps of exhaustion. © 1977 Academic Press, Inc. |
