S. RANZI 293 



nuclei: 1107 ± 24 m the control embryos; 1233 ± 28 in NaSCN 

 embryos; difference in the means is 126; standard error of differ- 

 ence is ±37, i.e., a significant difference. Furthermore SCN~ in- 

 duces chordal differentiation from cells of other organ rudiments 

 (Corti, 1950; Badinez et at, 1954). These authors obtained larvae 

 which, beside the normal notochord, had more or less extended 



Fig. 3. Cross sections of Triton embryos: A, control embryo; B, C, Li- 

 treated embryos; c, notochord; mi, somites. (From Lehmann, 1937.) 



sections of notochord, lateral or dorsal to the brain. Generally, 

 animalizing substances induce notochord formation from cells of 

 other presumptive rudiments; this is also shown by Lallier ( 1955). 

 He showed that sodium thiomalate, an animalizing agent in the 

 sea urchin, induces the formation of notochord in the ventral 

 explants of young amphibian gastrulae in which, therefore, the 



