No. 



BIOLOGICAL BULLETIN 



THE RELATION BETWEEN REGULATION AND 

 FISSION IN PLANARIA. 



C. M. CHILD. 



The data discussed below were obtained at various times during 

 the last five years from two species of Planaria, P. maculata and 

 an unnamed California!! species differing from P. maculata in 

 color, length of "auricles" and length of pharynx (Fig. 8), but 

 resembling it very closely as regards regulation and fission. 



I. THE POSITION OF THE PHARYNX IN PIECES FROM DIFFER- 

 ENT LEVELS. 



It has been known since Morgan's experiments on Planaria 

 maculata that the position of the newly formed pharynx in a 

 piece differs according to the level of the body from which the 

 piece was taken. According to Morgan the new pharynx arises 

 posterior to the middle of the piece in prepharyngeal pieces, its 

 distance from the middle decreasing as the level of the piece 

 approaches the pharyngeal region of the original animal ; as 

 regards postpharyngeal pieces, however, he states merely that the 

 pharynx arises anterior to or near the middle of the piece. My 

 own observations on prepharyngeal and pharyngeal pieces agree 

 with his. Figs, i and 2, at\ indicate this relation between level 

 and pharyngeal position. The regulation of postpharyngeal 

 pieces, however, presents a number of important features, which 

 Morgan has not, so far as I am aware, described. If the whole 

 postpharyngeal region be cut off as one piece, the new pharynx 

 always arises a considerable distance anterior to the middle 

 (Fig. 3) its position varying somewhat in different cases. If, 

 however, this region be cut into several pieces (Fig. 4, a, />, c, c/) 



