REGENERATION IN URONYCHIA 113 



regeneration of both parts, and in one of these (no, 37, the smaller 

 one died in 48 hours, so that only one (no. 21) gave two cells that 

 continued to live and in this case the organism was 24 hours old 

 when cut and probably about ready to divide. In all of the other 

 cases one part only regenerated normally. It is almost impossible 

 to cut these normal vegetative cells in such a way that no macro- 

 nucleus is retained, but the micronucleus, being single, is invari- 

 ably absent in one of the fragments. The power to regenerate 

 therefore, is only feebly developed during the vegetative period. 

 Out of 24 cases cut after the division period, only two gave com- 

 plete regeneration of both parts. 



In striking contrast to this result are the results of cutting dur- 

 ing the period of division, counting as the period of division the 

 time from the first external evidence (precocious formation of the 

 new cirri) until final separation. In all there were 37 experiments 

 on cells at this time, 7 of which were in the early stages, 14 in 

 the mid stages, 8 in the last stages, while 8 were multiple cuts. 



Analyzing these separately we find that of the seven cases cut 

 immediately before division, six continued the division in the origi- 

 nal plane forming two perfect cells in each case while the third 

 part, or portion cut off, formed a perfect cell in five cases. In the 

 majority of cases therefore, the original cell was made to form three 

 perfect cells so far as general form and motile apparatus are con- 

 cerned, and one of these parts in each case was without a micro- 

 nucleus and must have regenerated with only a portion of the 

 macronucleus. 



Of the fourteen cases cut during the mid phase of division, only 

 six formed three perfect cells each. Of the others, sometimes one, 

 sometimes the other fragment failed to regenerate, although macro- 

 nucleus material was present (in three cases the cut was directly 

 through the plane of division so that three cells were not formed; 

 in each of these two perfect organisms resulted.) 



No general rule was observed in regard to the regeneration of 

 cells cut during the late phases of division. When regeneration 

 occurred, vitality of the regenerated parts seemed low and the 

 life of the organism was short. Thus in experiment 10 both cells 

 were perfect in 4 hours, but one portion {B) soon became abnormal 

 and when killed after 72 hours showed a degenerated macronu- 



