REGENERATION IN URONYCHIA 



99 



for this and for other hypotrichous ciUates, all of the old cirri are 

 absorbed and new growths take their places. The new caudal 

 cirri for the anterior cell are precociously formed, the three dorsal 

 sickle-formed ones appearing first the others not appearing until 

 the division is well advanced (fig. 2). New membranelles are 

 similarly formed for both halves and a shifting of the axes of the 

 two connected cells gives ample room for the further develop- 

 ment of these appendages before complete separation (fig. 3). 



Fig. 3 Final stages in the division of Uronychia (camera drawings from prep- 

 arations). A, a late phase before separation; B, a cell immediately after division; 

 C, a cell fifteen minutes after division; D, a cell one hour after division. 



During these precocious formations, the nucleus gradually 

 prepares for division. The first step is the fusion of the large 

 masses of chromatin into a single band-formed nucleus (fig. 2, 

 A, B). This fusion is not completed until after the new cirri are 

 well advanced in growth. The micronucleus is very minute and 

 partly embedded in the macronucleus, nevertheless it divides by 

 mitosis, a minute spindle being formed. The macronucleus 



