112 



INDUCTION AND ORGANISATION 



Fig-. 40. Organiser activity in amphibians, (a) neurula of Triton 

 taeniatus, with (b) a secondary neural plate at the ventral side, 

 induced by a piece of dorsal marginal zone material from T. crista- 

 tus, part of which is still visible as a narrow white band in the 

 neural plate; (c) embryo of T. taeniatus with a secondary embryo 

 primordium (with neural tube, somites, ear-vesicles, and protruding 

 tail-bud) in its left side; (d) cross section of the embryo of fig. (c), 

 showing primary embryo primordium on the left, secondary pri- 

 mordium on the right; the latter consists partly of the light tissues 

 of the organiser, partly of the dark material of the host. After 



Spemann and H. Mangold. 



