INTERNAL FACTORS OF REGENERATION IN ANIMALS 



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the anterior surface of a short posterior piece, correspond to a differ- 

 ent part of the worm from that which would be expected to develop, 

 if the polarity of the piece is taken into account. Another reversed 

 head develops on the posterior cut-surface of the anterior piece, and 



FlG. 16. A. Head of Planar ia lugubris with line indicating level at which A 1 was cut off. 

 A 1 . Head of last regenerating a new head at its posterior end. B. Piece of P. maculata re- 

 generating head at each end. C. Posterior end of Allolobophora faetida regenerating a new 

 tail at its anterior end. C 1 . Enlarged anterior end of last with new tail. C*. Tip of new tail. 

 D. Anterior end of one individual of A. fastida, grafted to anterior end of another worm, 

 leaving posterior end of piece exposed. This has begun to regenerate. E. After Hazen. 

 Similar experiment in which a new head regenerated at posterior end of grafted piece. 

 F. Two longer pieces of A. fxtida united by anterior ends. One end was subsequently cut 

 off and a new tail regenerated. G. End of a developing piece of Tubular ia mesembryanthe- 

 mum that had been cut off; it has regenerated, at its proximal end, another proboscis. 



another tail on the anterior end of the posterior piece. The polarity 

 of the new part is in this case reversed, as compared with that of 

 the piece from which it arises. In the earthworm there is a marked 

 delay in the regeneration of these heteromorphic parts. Even in 

 tubularia in which heteromorphosis takes place, there is usually a 



