Regenerations Indicate Central Zone 61 



ing the entire animal. If a fifth part of the body disc 

 remains regeneration can occur in exceptional cases. If 

 half of the disc is present the absent parts are always 

 reformed. 



If one amputates all five arms of the same animal by 

 five transverse cuts, the first one very near the body, the 

 others at four different distances from it, then after a 

 certain time, the same for all five arms, the regen- 

 erated portion is largest for the first, and proportionately 

 smaller for the other four according as the site of amputa- 

 tion was farther from the central disc. 



This regenerated part which has developed from the 

 amputated arm is much smaller in diameter than the 

 original arm which was cut off. That is an indication 

 that the regeneration is not produced by the cooperation 

 of all the parts immediately adjacent to the surface of 

 amputation. 35 



These experiments thus seem to indicate a distinct 

 zone from which the process of regeneration proceeds 

 and to the activity of which it is due. 



From another side the existence of this formative 

 central zone is almost required by the results of the 

 similar experiments of Roux, which we have mentioned 

 above, on the formation of half embryos of frogs. 



These experiments show, in brief, that each half, right 

 or left, anterior or posterior, can develop independently. 

 If one admits also that this development is always en- 

 tirely epigenetic in nature, that is that it is due entirely to 

 correlative differentiations which the cells produce in one 



35 Helen Dean King: Regeneration in Asteria vulgaris. Arch. f. 

 Entwicklungsmech, d, Org., Band, 7. Heft. 2. and 3. Leipzig, Engel- 

 mann. October 18, 1898. P. 351361. Table VIII, especially 

 Fig. ii. 



