INTERNAL FACTORS OF REGENERATION IN ANIMALS 



45 



in earthworms (Fig. 20, D\ both for the anterior and posterior ends. 

 I have shown that it also takes place in the tail of a teleostian fish, 

 fundulus (Fig. 20, C\ and have offered the following explanation of 

 the phenomenon. The new material that is first laid down is, to a 

 certain extent, indifferent as regards its axes. A symmetrical struc- 



\ 



FlG. 20. A, A*. After Driesch. A. Piece of stem of tubularia cut off obliquely, showing oblique 

 position of tentacles. A 1 . Same, later stage. D. After Barfurth. Tail of tadpole regenerat- 

 ing from oblique surface. C. Tail of fundulus regenerating from oblique surface. D. After 

 Hescheler. Anterior end of allolobophora regenerating from oblique surface. . Piece of 

 planaria, cut off by two oblique cuts, regenerating new head and tail, f, f l , /' 2 . Three 

 stages in the development of a new head (of a piece of bipalium) at anterior end of oblique 

 surface. 



ture is then formed, with the old edge as a basis. The median 

 point of the cut-edge connected with the median point of the outer 

 surface of the new edge, gives the axis of symmetry of the new tail. 

 The other regions assume corresponding positions. In the tail of 

 the tadpole the position of the new notochord is determined by the 



