FIELDS AND GRADIENTS 



291 



r\ 



u 



\J 



E 



17 



D 



Fig. 138 

 Induction by grafts in stems of the hydroid Corymorpha. The grafted fragment 

 is shown stippled. A-C, Distal fragments of stem engrafted at proximal levels in 

 the host stem. A, An early stage. B, C, Two specimens after 48 hours' develop- 

 ment. The graft induces an outgrowth, which it organises to form a complete 

 large hydranth. D-E, Proximal fragments, of stem engrafted at proximal levels 

 in the host stem, after the same length of time as B and C. The resultant hy- 

 dranth is smaller (D) or subnormal and delayed (E). (From Child, Physiol. Zool. 

 II, 1929.) 



19-2 



