Slide showing two microscopic photographs of the 'Embyro of Triton Taeniatus with closed neural tube and optic vesicles.' Slide shows two microscopic photographs of the 'Embyro of Triton Taeniatus with closed neural tube and optic vesicles.' Title below images reads: 'Fig. 134, a and b. Embyro of Triton Taeniatus with closed neural tube and optic vesicles. On its ventral side a secondary embryo has developed: its anterior end is fused with that of the primary embryo and takes part in the formation of the optic vesicles. This secondary embryo has been induced by a piece of upper blastopore lip of a late gastrula ("Trunk organiser") which had been implanted at the level of the head. (After Spemann, 1931a.)' Late 19th to early 20th century