REGENERATION IN PARAMECIUM CAUDATUM. 169 



through the center should be followed by normal division of the 



surviving half, and this is the case. If the cut is made through 



either of the other planes we should expect division in the original 



plane resulting in a small and a large individual, but if the cut 



were made in front of the most anterior plane or 



back of the most posterior one there would be two 



opposing division areas in the same fragment and 



a reorganization would be necessary; thus both 



planes would disappear and a new one would form 



which would bring about symmetrical division. 



The results of the experiments that I have made 



seem to support this theory, but in order to test Diagram of 



the validity of the suggestion it would be necessary mature cell 



to make careful measurements of each cell used, 



gions of divi- 



and it would scarcely be possible to determine s j on p i an es. 

 with exactness whether or not the cut were made 

 through the region of a division plane or on one side of it. 



The fact that a loss of cytoplasm from such a highly differenti- 

 ated organism as Paramecium does not affect the size of the race 

 is one more proof of the necessity of seeking some way of reaching 

 the nucleus, for if some of the nuclear material could be removed 

 the result might be very different. So far I have found it im- 

 possible to keep a fragment alive after injury to the nucleus. 

 It is possible that after repeated removal of cytoplasm from the 

 same cell a small race size could be established, but the diffi- 

 culties of the operation and the great disturbance produced by 

 it in the cell would render the experiment practically impossible. 



SUMMARY. 



1 . When the anterior end of the cell was removed by a trans- 

 verse cut through the peristome just in front of the macro- 

 nucleus, thirty-four per cent, of the fragments regenerated the 

 lost end and divided normally. When the posterior end was 

 removed by a similar cut, back of the mouth, sixty-two per cent. 

 of the nucleated fragments regenerated the lost end and formed a 

 normal race. 



2. Removal of the anterior end resulted in irregular division 



