VITALITY 



485 



ten lioiirs old after division (Fig. 202). At this time the normal 

 individual is fully grown and active. At the age of sixteen to eigh- 

 teen hours different results are obtained. If a number of individuals 

 are cut at this age a small percentage of the anterior parts without 

 micronuclei will regenerate into perfect indi^■iduals save for absence 



Fig. 202. — Uronychia transfuga, merotomy and regeneration. 1, cells immediately 

 after division, cut as indicated; 2, fragment A of 1, three days after the operation, 

 no regeneration; .3, cell cut five hours after division; 4, fragment A of .3, three days 

 after operation, no regeneration; 5, cell cut at beginning of division as indicated, into 

 fragments A and B, C: A',B',C', fragments A, B, and C, twenty-four hours after the 

 operation; fragment A regenerated into a normal but emicronucleate individual 

 A', B, C, divided in the original division plane forming a normal individual C", 

 and a minute but normal individual B'. (After Calkins.) 



of the micronuclei; the posterior parts always regenerate. This 

 percentage rises to 100 per cent of cases w^hen individuals tw^enty- 

 four hours old are cut. Under the conditions at the time the 

 ex])eriments were made divisions occurred in normal animals at 

 inter\als of twenty-six hours. Older cells when cut frequently 



