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 of alterations (unpublished research).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 



