. 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 299 Raven (1952) carried out extensive research on Limnaea stag- nalis (gasteropod). LiCl-treated embryos develop as exogas- trulae (Fig. 9) in which, as in those of ascidians, no entodermiza- tion occurs, but the animal pole organs are reduced just as the cil
. 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 299 Raven (1952) carried out extensive research on Limnaea stag- nalis (gasteropod). LiCl-treated embryos develop as exogas- trulae (Fig. 9) in which, as in those of ascidians, no entodermiza- tion occurs, but the animal pole organs are reduced just as the ciliar tuft of the sea urchin. Monsters with convergent eyes, cyclopy, and anophthalmia have been described. Arendsen de Wolff-Exalto (1947) did not notice any change in determination due to NaSCN action. A comparison between the alterations noted in the two mol- luscs has not been made. However, an outstanding fact is the. Fig. 9. Topographical relationship in Limnaea exogastrulae: A, nor- mally developed organ rudiments; B,C, reduced organ rudiments at the animal pole; , large-celled ectodeiTn; en., entoderm; m., marginal zone; s. ect. small-celled ectoderm; st, stomodaeum. (From Raven, 1952.) identity of the series of cyclopic monsters induced by LiCl in both. It is difficult to carry out a comparati\'e analysis based on egg organization. LiCl inhibits rudiment development at the animal half in sea urchins and Limnaea. This does not occur in amphib- ians and in Ciona in which LiCl affects the notochord that is a rudiment on the equatorial level of the egg. As a result, an inter- pretation on the basis of comparative morphology does not seem possible. Differences in Proteins from Embryos Showing Different Malformations Research carried out in our laboratory many years ago showed that ions inducing colloid precipitation also induce vegetalization in sea urchins (Tamini, 1943b) and cyclopic monsters in Am- phibia (Tamini, 1943a). Conversely "swelling" ions induce sea
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