262 



BIOLOOY OF THE PROTOZOA 



region. Except for mutilations these regenerations and replace- 

 ments occur only at periods antecedent to cell division and indicate 

 some far-reaching change in the constitution of the protoplasmic 

 make up. The ability to undergo such a change furthermore is 

 progressive as shown by experiments in cutting Uronychia (Calkins, 



Fig. 135. — 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 BC; A',B',C", fragments A, B, and C, twenty-four hours after the 

 operation; fragment A regenerated into a normal but amicronucleate individual 

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

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



1911). In these experiments the cell if cut immediately after divi- 

 sion in a plane indicated by the section line (Fig. 135) is divided 

 into two fragments, one of which, the posterior with giant cirri, 

 contains the single micronucleus, while the anterior portion, with 

 peristome, contains a part of the macronucleus but no micronucleus. 



