REGENERATION IN PARAMECIUM CAUDATIM. 



161 



The survival of both pieces depends largely on the stage of 

 fission reached at the time of the operation. The nearer the 

 process is to completion the more likely is the recovery of both 

 halves. 



Experiment 2. When the cut was made through the center of 

 the anterior or the posterior half of the dividing cell (Fig. 6, X and 

 Z) the small non-nucleated piece always died, and the large piece 

 continued to divide in the original plane forming a small cell 

 (Fig. 7, C) and a large cell (>). 



Experiment j. When the cut is made in either half of the 

 dividing cell near the plane of division (Fig. 8, X and F) the 



6 78 9 



FIG. 6. Dividing cell showing the region of the cuts. 



FIG. 7. Small and large individual formed by division in the original plane 

 after removal of the anterior end of a cell during the process of fission. 

 FIG. 8. Diagram showing cuts made near the center of a dividing cell. 

 FIG. 9. Cell with fragment of the posterior half still attached. 



small fragment (Fig. 9, B) remains attached to the other half, 

 and is gradually absorbed. In a few r cases division continued in 

 the original plane, but this occurred only in those cells where 

 fission was almost completed at the time of the operation. 



E. The Effect of Cutting Cells During Conjugation. 

 During epidemics of conjugation pairs which had become 

 firmly united were isolated and from these either the anterior 

 or the posterior ends were removed (Fig. 10, X and 7). None 

 of the pairs were cut through the center. The non-nucleated 

 fragments always died shortly after the operation, while the 

 larger ones either remained in contact for several hours or sepa- 

 rated at once. Regeneration in these pieces is exceedingly slow 

 and fission is greatly delayed. Truncated fragments (Fig. n. 



