164 T. H. MORGAN AND ALICE E. SCHIEDT. 



(/) Two of the tenth pieces have not formed new pharynges, 

 the third has a new central and two new lateral pharynges. 



In another series (C) the planarians were cut into the three 

 regions of the body --head, pharyngeal and tail parts and then 

 each of these were cut into very small cross-pieces ; they were 

 kept nineteen days and then killed. In the head pieces a new 

 central and from three to five new lateral pharynges have devel- 

 oped. 



The pieces from the pharyngeal region give no results as the 

 pharynges are too advanced for one to be able to determine 

 which of the pharynges are old and which are new. 



One of the tail pieces had no pharynges developed. The 

 others had a central and from four to six new lateral pharynges 

 regenerated. 



The only other study that has been made of the regeneration 

 of Phagocata gracUis is that of Lillie in iQOi. 1 He showed that 

 "the power of regeneration of this genus is equal to that of 

 Planaria." He also pointed out that in cross-pieces several 

 pharynges regenerate simultaneously, although the more anterior 

 ones are the most advanced. Each pharynx develops at first in 

 a separate cavity of its own and the cavities fuse together to form 

 a common pharyngeal cavity. We have also observed this mode 

 of development. Lillie found that in lateral pieces new pha- 

 rynges first arise on the old side of the piece and the new ones on 

 the opposite, regenerating side do not appear until a branch of 

 the intestine has extended into this region. The new pharynges 

 connect at one end with this branch. 



CONCLUSIONS. 



The regeneration of cross-pieces from different levels shows 

 the following relations. 



1. Pieces anterior to the old pharyngeal chamber produce in 

 the new tissue at the posterior end a new median pharynx and 

 lateral pharynges that increase in number from before backwards. 



2. Pieces containing only the old median pharynx develop 

 new lateral ones from the sides of the pharyngeal chamber. 



'Lillie, F. R., " Notes on Regeneration and Regulation in Planarians," Amer. 

 Joitr. Physiology, VI., 1901. 



