462 GARY N. CALKINS 



Finally, a word as to the effect of cutting individuals which 

 are ready for conjugation. Selecting a conjugation test in which 

 conjugation was just beginning, a number of individuals were 

 removed and cut. Some of these were preparing for fusion, as 

 indicated by characteristic maneuvers, and undoubtedly would 

 have conjugated had they been left together. Forty-three 

 individuals were successfully cut through the anterior end, after 

 which they were treated in the same manner as cut conjugants. 

 All regenerated, but not one showed the slightest evidence of 

 reorganization, as shown by the formation and development of 

 the macronuclear vesicle. Traumatic conditions were ineffective 

 in starting up the series of changes characteristic of conjugation. 



DISCUSSION 



Although there is nothing in the literature nor in the history 

 of Uroleptus to furnish a basis for specific expectations of any 

 kind, the behavior of the cut conjugants was entirely unexpected. 

 It was highly surprising to find that the course of events followed 

 by the cut fragments was exactly the same as that of a normal 

 ex-conjugant, despite the fact that no interchange of nuclei had 

 taken place, and protoplasmic fusion had lasted for only a frac- 

 tion of the usual time. The results indicate an 'all or none' 

 reaction of the cells following upon fusion of two individuals at 

 the anterior ends and involving the entire sequence of matura- 

 tion phenomena. 



The full history of the nuclei during conjugation and during 

 the period of reorganization following conjugation was de- 

 scribed in the first of these studies on Uroleptus. ^ The conjugat- 

 ing individuals separate shortly after nuclear interchange and 

 fusion and the subsequent reorganization processes take place in 

 the separated ex-conjugants. The latter processes require from 

 five to six days for completion, and the general course of events 

 may be followed from day to day by characteristic changes 

 of the newly formed macronucleus, which is easily visible in the 

 living animal. Twenty-four hours after separation, this new 



^Calkins, Uroleptus mobilis, I, loc. cit. 



