. 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. 292 EARLY DETERMINATION IN DEVELOPMENT (1954): vegetalized embryos show a smaller ciliar tuft at the animal pole than the controls; these embryos develop into larvae in which the ectoderm is reduced whereas the entoderm is hyper- developed and in certain instances it p
. 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. 292 EARLY DETERMINATION IN DEVELOPMENT (1954): vegetalized embryos show a smaller ciliar tuft at the animal pole than the controls; these embryos develop into larvae in which the ectoderm is reduced whereas the entoderm is hyper- developed and in certain instances it protrudes (exogastrulae). The animalized embryos develop with a very large ciliar tuft; in these embryos entoderm and mesenchyme are reduced. Vertebrate cyclopic embryos, obtained by Stockard (1907) in Fundulus and by Cotronei (1922) in amphibians through the ac- tion of MgCl2 and LiCl, may be considered as originated from the same causes which induce vegetalized larvae in sea urchins. Adelmann (1934) and Lehmann (1937) showed that LiCl in- duces an inhibition of prechordal plate and of the notochord in. Fig. 2. Animalized sea urchin embryos. (From Lindahl, 1936; Tamini, 1941; Backstrom, 1953.) amphibians (Fig. 3). Therefore the cyclopy originates from a disturbance in the induction process, and the hypodevelopment of the notochord and of the prechordal plate corresponds to the sea urchin vegetalization. Later Backstrom (1953) showed a re- duction in organ development and in the animal half of the Xenopus embryo (therefore small embryo). So far we are unable to state whether this phenomenon can be observed in other am- phibians. An increase of notochord in the amphibians is induced by NaSCN (Ranzi et al, 1946) (Fig. 4). Statistical research carried out by Corti at Milan on Rana esculenta embryos in the tailbud stage showed the following average number of notochordal cell. Please note that these images are extracted from scanned page images that may have been digitally enhanced f
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