Dimensions of the notochord and somites in embryos of Xenopus laevis treated with thiocyanate.

As a result of previous research, Ranzi & Tamini (1939) pointed out that the notochord of Amphibian embryos of several species treated with sodium thiocyanate (NaSCN) solutions is larger than the notochord of control embryos. Later, several substances were identified which cause enlargement of the notochord: full data and a complete review of the literature on this subject are given by Ranzi & Citterio (1954) and Ranzi (1957). A careful statistical study on the number of nuclei in Rana esculenta embryos was carried out by Corti (1950). In embryos which had been treated for 24 hours with 0-05 M NaSCN, from the late blastula stage onwards, she found 1233 + 28 nuclei at the tail-bud stage, whereas the controls reared in spring-water had only 1107 + 24 nuclei: these two sets of data are significantly different (standard error of the difference ±37). Enlargement and induction of notochord by NaSCN treatment have been reported by Badfnez, Carrasco, & Manriquez (1954). Notochord can be obtained from ventral explants and from explants of presumptive mesoderm by means of urea, which acts like NaSCN (Leone, 1952), or by means of NaSCN (Ogi, 1957a). However, Ogi (1957W counted the nuclei of a few embryos of Bufo vulgar is and JR. nigromaculata treated with NaSCN and Nal and was unable to demonstrate an increase. For these reasons we thought it useful to repeat the work of Corti, but on another species, Xenopus laevis (Daudin), which appeared to be very sensitive to substances causing alterations of development (for the effect of LiCl see Backstrom, 1954).