REGENERATION IN PARAMECIUM CAUDATUM. 



1 63 



they had separated each cell was isolated in a drop of the cuture 

 fluid. A period of two to five hours was allowed for growth, then 

 the cells were cut and the further development of the nucleated 

 fragments observed. The power of regeneration is present in 

 these cells, but very few recover from the operation. In the 

 actively growing cell the cytoplasm is in a less viscid state than 

 it is in the vegetative cells, and it is for this reason that injury to 

 the ectosarc results, in ninety per cent, of the operations, in the 

 escape of the entire contents of the cell. In successful operations 

 removal of the anterior or the posterior end give the same 

 general results as in the vegetative cells. The most striking 

 fact brought out is that as early as two and a half hours after 

 fission the next division plane is determined. A brief description 

 of a few experiments will demonstrate this. 



R. 28. Two sister cells were isolated two and a half hours 



FIG. 13. Two sister cells cut at the same time, showing the formation of a 

 normal race from the one from which the posterior end was removed, and the 

 irregular cells formed from the cell from which the anterior end was removed. 



after fission ; the anterior end of one and the posterior end of the 

 other were removed (Fig. 13, A and P). On the following day 

 the nucleated fragments were active but had not yet divided. 

 By noon of the same day A had formed two normal cells and P 

 had divided into a small and a large cell. Later the smaller cells 

 grew to the normal size; they were then killed. 



