74 



GROWTH AND MORPHOGENESIS 





Fig. 27. The organizer of a gastrula blocked by a heat shock has been grafted 



into a normal host: it has differentiated into chorda and intestinal lumen 



and it has induced somites and neural masses (Brachet, 1957). 





-'^i 



'K<: 



Fig, 28. RNA-rich, basophilic crescents forming in ectoderm cells which have 

 been exposed to an alkaline shock (Brachet, 1957). 



