Med. I 



Q ; » (« * ^1>''^V sec. Med. 



Fig. 19 



The induction of secondary embryos by organiser grafts, a. Dorsal view showing 

 primary embryo of Triton taeniatiis, b. Side view showing secondary embryo 

 induced by grafting an organiser of T. cristatus (distinguishable by lack of 

 pigment) into the flank of a. c, Dorsal view of secondary embryo, and left side 

 view of primary embryo, at later stage ; note ear- vesicles of secondary embryo in 

 line with that of primary, d. Transverse section through c. Med. neural tube of 

 primary embryo; r. sec.Pron. pronephric duct; r.sec. Uw. mesodermal somite; 

 sec.Ch. grafted notochord; sec. D. gut; sec. A'led. neural tube; of secondary 

 embryo. Note that most of the structures of the secondary embryo have been in- 

 duced from host tissues, but that the graft has contributed to some (distinguishable 

 by lack of pigment). (From Spemann and Mangold, Arch. Mikr. Anat. u. 

 Ejitzvmech. c, 1924.) 



4-2 



