. The beginnings of embryonic development : A symposium organized by the Section on Zoological Sciences of the American Association for the Advancement of Science, cosponsored by the American Society of Zoologists and the Association of Southeastern Biologists, and presented at the Atlanta meeting, December 27, 1955. Embryology. S. RANZI 295 presumptive rudiment of the notochord is not present. The same phenomena, although with small notochord sections (Fig. 5), were observed by Leone working with urea, when it was recog- nized that proteins are denatured by animalizing substances. On the othe
. The beginnings of embryonic development : A symposium organized by the Section on Zoological Sciences of the American Association for the Advancement of Science, cosponsored by the American Society of Zoologists and the Association of Southeastern Biologists, and presented at the Atlanta meeting, December 27, 1955. Embryology. S. RANZI 295 presumptive rudiment of the notochord is not present. The same phenomena, although with small notochord sections (Fig. 5), were observed by Leone working with urea, when it was recog- nized that proteins are denatured by animalizing substances. On the other hand, notochordal sections appear in the whole embryo treated with urea (Jenkinson, 1906; Fautrez, 1951; Leone, 1953). Leone recognized in these embryos the same developmental al- terations which are induced by SCN" and I~. The alterations shown by older embryos with larger notochords are described by Ranzi et al. (1946). These alterations (Fig. 4) are: an increase in hindbrain dimensions, the formation of ganglia from the roof of. Fig. 5. Section through ventral explantate of Rana esculenta gastrula treated with urea: c, notochord; 1, lentoid. (From Leone, 1952.) the hindbrain, the epiphysis duplication, the hyperdevelopment of lateral line organs, the formation of epithelial vesicles from the epidermis, the abnormal proliferation of epidermis. Rana escu- lenta embryos treated with iodosobenzoate show the same kind of alterations (unpublished research). Whether the alterations in the nervous system are induced by the enlargement of the notochord or by an excess of active evocat- ing substances is a problem which seems to be solved by the presence of nervous rudiments in axolotl ventral explants treated with NaSCN (Ranzi and Tamini, 1941). In this instance the notochordal rudiment is absent and evocating substances must. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance o
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