MORPHOLOGY AND PHYSIOLOGY OF GENUS URONYCHIA 375 



Cells cut in mid-division 



Summary of table S. Ten individuals of U. setigera were cut 

 at about the middle of the division process. At this time the 

 micronuclei were somewhat separated and a single cut could not 

 destroy both unless it was made in a longitudinal plane. Two 

 individuals were cut in the plane of division. The resulting 

 cells developed to be normal animals just as if the usual division 

 process had been completed. In six cases where either the pos- 

 terior or anterior end of the dividing animal was removed, divi- 

 sion was not disturbed, but was completed before any regenera- 

 tion took place. The small amicronucleate parts were probably 

 injured by the cutting in one or two cases, for no regeneration was 

 recorded for two of them and in the other four only slight regenera- 

 tion was listed. The large pieces completed division in the 

 usual time. Afterwards the injured cells replaced the missing 

 parts. In one case (no. 69) where the cut was in the median 

 longitudinal plane (long. B), division was completed in both 

 fragments, but only those of the left side, the ones with micronu- 

 clei, regenerated. Experiment no. 84 is particularly interesting, 

 for the cut was oblique E. This divided the animal so that when 

 division was completed there was a small and a large cell originat- 

 ing from both the posterior and the anterior half. Neither of the 

 smaU pieces regenerated. Both of the large pieces reformed 

 the missing parts, but only one of them divided. Probably the 

 micronucleus of the anterior half was destroyed, for the cut was 

 about in its region. 



Cells cut in late division 



Summary of table 9. Six individuals of U. setigera were cut 

 in late division stages. In general the results correspond to 

 those obtained from cells cut slightly earlier. When cut trans- 

 versely division proceeded normally and the injured cells re- 

 generated after division. This transverse cut was made in 

 two experiments (nos. 20 and 35). The amicronucleate parts 

 cut off died very soon, in one case without any, in the other with 

 slight regeneration. Two individuals were cut in the median 



