REGENERATION IN THE PLANARIAN PHAGO- 



CATA GRACILIS. 



T. H. MORGAN AND ALICE E. SCHIEUT. 



Pliagocata gracilis differs from other planarians in having a 

 number of pharynges in a common pharyngeal chamber. There 

 is a large median anterior pharynx, and 12 or 14 lateral 

 pharynges arranged along the sides of the chamber. The object 

 of the following study was to determine the sequence in the re- 

 generation of the pharynges in pieces from different regions of 

 the body. The particular point that we had in view in beginning 

 the work was to examine the origin of the new pharynges in 

 pieces cut posterior to the region of the old pharynges. It has 

 been shown for other planarians that pieces from this region of 

 the body produce a new pharynx at or near the anterior end, and 

 the question arose as to what would occur in a form like Pliago- 

 cata having several pharynges. Would the median pharynx first 

 appear and new ones be added behind this one ? This would 

 indicate that a growing region was also present behind the first 

 pharynx, while in other planarians the growing region in pieces 

 of this kind appears to be mainly anterior to the new pharynx. 

 It seemed not improbable that a single anterior pharynx alone 

 might develop and produce a mono-pharyngeal worm ! Other 

 similar questions arose in connection with the regeneration of new 

 lateral pharynges in more anterior pieces. 



The regeneration of the pharynges, in cross-pieces from the 

 following regions of the body, was studied : 



A. Worm cut transversely into five pieces. 



1 . Head-piece without any pharynges. 



2. Median piece with old median anterior pharynx. 



3. Middle piece with several lateral pharynges. 



4. Posterior piece with posterior pair or pairs of lateral 

 pharynges. 



5. Tail piece without any pharynges. 



B. Worm cut transversely into ten pieces. 



1 60 



