EMBRYONIC INDUCTORS AND ORGANIZERS 



457 



The earlier experiments were on urodeles, chiefly Triton; but work with 

 anura and heteroplastic and xenoplastic transplantations between dif- 

 ferent urodele species, between anuran species, and even between urodeles 

 and anura have shown beyond question that the presumptive chorda- 

 mesoderm acts as inductor in amphibians generally and that its action is 

 not species-, genus-, or even order-specific; but tissues and even embry- 



FiG. 157, A-C. — Induction of a secondary neural plate and embryonic axis in ectoderm by 

 implantation of dorsal lip material. A, B, two views of Triton taeniatns neurula with secondary 

 neural plate induced by heteroplastic implant from dorsal lip of T. cristatns; C, later stage of 

 same embryo with secondary embryo on left side (from Spemann und H. Mangold, 1924). 



onic extracts of some forms are toxic for some other species.'" Since ac- 

 tion of the living dorsal inductor, is, to such an extent, independent of 

 species, the question at once arises as to the nature of its action, whether 

 material or dynamic. This question has been raised and discussed by 



" Geinitz, igasa; Bytinski-Salz, 1929a, b, c; H. Mangold, 19296; O. Mangold, 1929&; 

 Schotte, 1930; Raven, 1931, i933&,- G. A. Schmidt, 1933, 1936a, b; Holtfreter, 1935a, 6, 1936. 

 See also Twitty, 1937, "Experiments on the phenomenon of paralysis produced by a toxin 

 occurring in Tritiints embryos," Jour. Exp. ZooL, 76; Horsburgh, Tatum, and Hall, 1940, 

 "Chemical properties and physiological actions of Trikirtis embryonic toxin," Jour. Pharmacol. 

 E.xp. Therapeutics, 68. 



