. The elements of experimental embryology. Embryology, Experimental; Embryology. 488 APPENDIX gastrulation is not complete, but a portion of the ectoderm has been underlain by endo-mesoderm and has been organised. In such portions, the direction of ciliary beat is regular and normal, while remaining irregular over the rest of the epidermis (fig. 218). This brings us to a more general consideration of partial exo- gastrulation. Total exogastrulation is a comparatively rare occur-. I s. Fig. 218 Induction of polarity in epidermis by underlying organiser. The direction of cilia-beat (indicated by
. The elements of experimental embryology. Embryology, Experimental; Embryology. 488 APPENDIX gastrulation is not complete, but a portion of the ectoderm has been underlain by endo-mesoderm and has been organised. In such portions, the direction of ciliary beat is regular and normal, while remaining irregular over the rest of the epidermis (fig. 218). This brings us to a more general consideration of partial exo- gastrulation. Total exogastrulation is a comparatively rare occur-. I s. Fig. 218 Induction of polarity in epidermis by underlying organiser. The direction of cilia-beat (indicated by arrows) of non-underlain epidermis is irregular and chaotic; that of epidermis underlain by organiser-tissue is regular and polarised. (From Holtfreter, Biol. Zentralbl. Liii, 1933.) rence: in the majority of cases, exogastrulation only proceeds to a certain point, and then the remainder of the endo-mesoderm is invaginated under the ectoderm. All gradations are to be found from a minimal invagination to a normal embryo. The first step is the presence of some blood- and yolk-cells in the ectodermic vesicle. When they are present, they induce a smooth two-layered epithelium, with normal tempo of differentiation, in place of the irregularly folded and wrinkled epidermis derived from wholly. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Huxley, Julian, 1887-1975; De Beer, Gavin, Sir, 1899-1972. New York [Hafner Pub. Co. ]
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Keywords: ., bookcentury1900, bookcollectionbiodiversi, booksubjectembryology
