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.®® 
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 
*5Helen Dean King: Regeneration in Asteria vulgaris. Arch. f. 
Entwicklungsmech, d, Org., Band, 7. Heft. 2. and 3. Leipzig, Engel- 
mann. October 18, 1898. P. 351—361. Table VIII, especially 
Fig. 11. 
