288 CHARLES RUSSELL BARDEEN. 



7. In regeneration the new ectodermal cells arise from the old 

 by direct division. New nerve cells, intestinal cells and muscle 

 cells seem likewise to arise from preexisting cells by direct di- 

 vision. It is possible, however, that they may spring from the 

 large cells of embryonic type situated in the parenchyma. From 

 the latter the other tissues mainly arise. 



8. The new pharynx arises immediately posterior and ventral 

 to the region into which the intestinal contents are forced by gen- 

 eral muscular contraction and in response to stimuli arising from 

 this region. 



9. A new head is regenerated only in tissue produced at a cut 

 surface, and with definite axial relations to the surface. The 

 direct stimulus to head formation arises from an exposed chief 

 coordinating region of the central nervous system. The head is 

 formed with radial symmetry about the tip of the main intestinal 

 branch extending to the cut surface in the vicinity of the exposed 

 nervous system. 



10. After head and pharynx have been differentiated the activi- 

 ties tending to restore the piece to a worm of normal form and 

 proportions become especially marked. 



11. During regeneration highly differentiated tissues are de- 

 stroyed unless they may be directly utilized in the formation of 

 new parts. 



