Slide showing five diagrammatic drawings of embryo experiments on a newt's egg Slide shows five diagrammatic drawings of embryo experiments on a newt's egg. The diagrams are labelled 'a' to 'e'. Title below images reads: 'Fig. 20. The presence of the organiser region is essential for development. a, A newt's egg constricted into two in the transverse plane, thus separating dorsal and ventral halves. b, The result of isolation of a dorsal half (Containing the organiser region); a perfect embryo. c, The result of isolating a ventral half (lacking the organiser region): a blastula-like ball of cells which develops no further. d, A newt's egg constricted in the plane of symmetry, thus separating lateral halves, each of which contains a portion of the organiser region, and, e, develops into a perfect embryo. (From Spemann, Naturwiss, IV, 1924)'. Late 19th to early 20th Century