REGENERA TION. 



I 97 



their migration in definite directions. Nevertheless, the assump- 

 tion gave a formal explanation of the phenomena. 



I shall next consider, in the light of the hypothesis of trans- 

 portation of specific stuffs, the results of certain experiments 

 that bear on the question. 



When an oblique piece is cut from a planarian, as indicated 

 in Fig. i, A, I find that the new head develops not from the 

 center of the piece but far up on one side, Fig. I, B\ and 

 always on that side that lay nearer to the head of the plana- 

 rian. The new tail develops out of that part of the posterior 

 side that was originally nearer to the tail of the planarian, Fig. 



D 



FIG. 2. 



i, B, C. The new pharynx appears in the middle of the piece, 

 with its long axis at first in the direction of the old long axis ; 

 but as the old part changes its form to produce the body of the 

 new worm, the pharynx comes to lie symmetrically with respect 

 to the new head and tail, Fig. i, D.^ 



If a piece is cut from the planarian by making two oblique 

 cuts that form an angle with each other, as shown in Fig. 2, 

 A, a new head develops, as before, at the most anterior part of 

 the anterior cut surface, and a tail at the most posterior part, 

 Fig. i, B. In this case, both head and tail lie on the same side 

 of the piece. The new pharynx appears in the middle, but not 

 in line at first with either the new head or tail. 



These experiments show that the position of the new head 



