386 



T. H. Morgan. 



of heteromorphosis in regions posterior to the old pharynx. An 

 important side light is thrown on the problem of axial polarity 

 and heteromorphosis by these relations. 



Cross-pieces of Planaria si7nplicissima, that are not too short, 

 from the region between the head and the pharynx-chamber regen- 

 erate a head on the anterior and a tail on the posterior cut surface, 



Fig. 14. The new pharynx is always situated at the posterior 

 edge of the old material. Similar cross-pieces from the region of 

 the pharynx-chamber also produce a head at the anterior end and a 

 tail at the posterior end. The new pharynx develops in the middle 

 of the piece in connection with the old chamber. Cross-pieces 

 from the region behind the old pharynx also regenerate a head at 



