114 



GARY N. CALKINS 



cleus. A similar result was obtained in no. 35. In no. 62 the 

 dividing cell was cut longitudinally; division was continued and 

 each fragment divided in the original plane thus forming four 

 fragments, not one of which regenerated. 



Of the four cases cut at the end period of division, only one 

 formed three perfect cells. All of the others behaved like cells 

 cut immediately after division. 



Of the eight cases of dividing forms in which the cell was cut 

 twice the results conformed with those of the dividing period 

 generally, although smaller pieces failed to regenerate and even 

 larger pieces including the original plane of division and much 

 macronuclear material failed to regenerate (see no. 19). 



Further evidence of the limitation of the maximum regenerative 

 power is given by the comparison of cells cut in exactly the same 

 relative portions of the cell, but at different periods of vegetative 

 life. Double regeneration occurred only when the cells were at 

 or near the beginning of the division period, never after division. 



One general result obtained from these experiments is that Uro- 

 nychia when cut does not divide as soon as the cell would have 

 divided had it not been cut. The average division rate of these 

 organisms under normal conditions is two divisions in three days; 

 in the cut forms the usual period required to divide is never less 

 than three days, or more than twice as long as the normal. Only 

 a few controlled experiments were undertaken with this point in 

 view and these are tabulated below: 



