a 



c 



a. 



6 



p.S, 



PLATE VI. The organiser and its activity, (a) Gastrula of Triton with im- 

 planted organiser (dark pigmentation) opposite the blastopore lip. (b) The 

 same embryo at the neurula stage, (ventral view) ; a secondary neural plate 

 has been induced, (c) The same embryo a few days later. A secondary embryo 

 primordium (right), with head and tail-bud has been formed at the side 

 opposite to the primary primordium. Both embryos have a common anus (a), 

 situated between the primary (p.s.) and secondary (s.s.) tail-buds. After 



Spemann. 



