EMBRYONIC RECONSTITUTIONS 



533 



tion (pp. 282-85). The map of Figure 170 shows in a different way regions 



from which tissues of certain organs differentiate in chorio-allantoic grafts. 



The results of grafting and explantation show a very considerable 



capacity for reconstitution in many of the isolated parts and a general but 



thyroid 

 liver 



respiratory tract 



aaterior gut 



5tomacH 



epltf^ellal tubules 



liver 



n;5pinitory tract 



anterior gut 



stomach 



epittielial tutniles 



thyroid 



resp tract 



anterior gut 



stcmacK 



epith tubules 



epithelial tubules 



thyroid 



Uver 



respiratory tract 



aaterior gut 



stomach 



epithelial tubules 



Uver 



respiratory tract 



anterior gut 



stomach 



epithelial tubules 



Fig. 169.— Regional distribution of development of entodermal structures in chorio-al- 

 lantoic grafts of head-process blastoderm of chick; circles at margin indicate pieces from which 

 "primordial germ cells" were obtained; measurements as in Fig. 167 (from Rawles, 1936, pre- 

 pared by Willier and Rawles). 



definite relation of character of reconstitution to a spatial pattern of some 

 sort. It seems evident that neural tissue can develop without induction 

 and that in earher stages the primitive streak may reconstitute from re- 

 gions lateral to those in which it normally originates; this is perhaps large- 

 ly a matter of continuation of the cell movements concerned in formation 



