174 



Regeneration 



Fig. 28 



erated (Fig. 28) ; but that if a piece acdbhe cut from a 

 Planarian obliquely (Fig. 29) instead of at right angles to 

 the longitudinal axis a tiny head is 

 formed at the foremost corner of the 

 piece a and a tiny tail at the hindmost 

 corner b (Fig. 30) . Why is it that in the 

 oblique piece the head is formed in the 

 corner and not all along the 

 cut surface as is the case when 

 the cut is made at right angles 

 to the longitudinal axis? The 

 writer is inclined to believe that 

 the right answer to this ques- 

 tion has been given by Bar- 

 deen. ' This author has pointed 

 out the apparent r61e that the 

 circulatory (or so-called di- 

 gestive) canals in Planarians 

 play in the localization of the 

 phenomena of regeneration, in- 

 as-much 



as the new head always forms 

 symmetrically at the opening of 

 the circulatory vessel or branch 

 which is situated as much as 

 Fig. 30 possible at the foremost end of the 



Fig. 29 



^Bardeen, C. R^Am. Jour. Physiol., I90i,v., i; Arch. f. Entwcklngs- 

 mech., 1903, xvi., i. 



