REGENERA TION 



Another experiment shows even more satisfactorily that the 

 material over an anterior cut-edge may produce one or more new heads 

 according to the conditions, and that the result is not connected with 

 the region from which the new material is derived. If the anterior 

 end of a planarian is cut off and then an oblong piece is removed from 

 the middle of the worm, as shown in Fig. 24, A, it will be found, if 



FIG. 24. Planaria lugubrls. A. Showing where a piece, 4, was removed from middle of a 

 worm, a, b. Regeneration of a single head, c , c 1 . Regeneration of two heads. D, E, F. Re- 

 generation of small piece, 4, that was cut out. 



the side parts are kept from fusing together in the middle line, that a 

 new head develops at the anterior end of each part, as shown in Fig. 

 24, c, c l . If, on the other hand, the two sides come together and fuse 

 in the middle line, as shown in Fig. 24, a, b, the new material that 

 appears over their anterior ends becomes continuous and produces 

 a single head. In this case, although the middle part of the old 

 tissue has been removed, a single head develops that is normal in all 

 respects, and the eyes are not nearer together than when the middle 

 part is present, as when regeneration takes place from an anterior 

 cross-cut surface. 



The assumption that the lateral position of the head on an oblique 

 surface is connected with the more anterior region of the old material 

 that is found at that side, can be made at least more intelligible by 

 the following experiment : If the head of a planarian is cut off 

 obliquely, as indicated in Fig. 21, B, so that one of the " ears " is left 

 at one side, the new head arises at the side in connection with the 

 part of the old head that lies at that side. The new head does not 

 extend over the entire cut-surface, which is longer of course than a 

 cross-cut would be, but lies at one side, as in the other cases just 

 described. In this case we can see that if the new head cannot, on 

 account of certain conditions, extend over the entire cut-surface, one 

 side of it may be determined by the presence of a part of the old head, 



