a 



, m^zW'^ ♦ » * ifg,~ 





^^. 





PLATE VII. Head- and trunk organiser, (a) Part of the blastopore lip 

 of an older gastrula has induced a secondary primordium, of a trunk-like 

 nature, in the trunk of the host. The two embryos are parallel. In both, the 

 notochord is sectioned lengthwise (pr.ch. and s.ch.), whereas the neural tube 

 is sectioned at two places (pr.n. and s.n.). The somites of the two embryos 

 may be seen on both sides of each notochord. (b) Part of the archenteron 

 roof of an older gastrula has induced a piece of fore-brain, with eye-vesicles 

 (S.O.), in the trunk area of the host, (cf. Fig. 47a). After Spemann. 



