IQO THE BIOLOGY OF STENTOR 



from folding upon itself with resulting stripe distortions (Fig. 50B). 

 The pieces soon pulled apart but not before straight-line healing 

 had occurred. In 4 cases, the narrow fragments did fail to form 

 primordia though they had no mouths, retained sufficient macro- 

 nuclear nodes, and survived and were active for about 5 days. It 

 is therefore possible that in an almost completely symmetrical 

 system there may not be sufficient difference or anisotropy of 

 pattern for oral differentiation. Such specimens presumably were 

 entirely capable of producing primordia, since much smaller 

 fragments do, but apparently failed to do so because of the 

 absence of any guidance in where to produce them. The attempt 

 to produce anisotropic systems by grafting together patches of 

 fine striping from the center of the cell and comparable patches 

 of wide striping, however, was not successful; always sufficient 

 l.s.c. remained and primordia were formed at these places. 



5. Competition among loci of stripe contrast; regeneration 

 and obliteration of primordium sites 



Although the number of primordia is usually equal to the 

 number of loci of stripe contrast, this correspondence is apparently 

 modified by competition among primordium sites. Thus it usually 

 happened that in grafts of two longitudinal aboral halves in which 

 membranellar band remnants remained and delayed the onset of 

 regeneration a primordium was formed in only one of the minor 

 l.s.c. and a single stentor resulted, as if one site became dominant 

 over the other (Tartar, 1956a). This effect could work either way. 

 Two aboral halves were grafted with a complete primordium site 

 and regeneration was delayed; two primordia were produced, 

 instead of one in the major primordium site. This was explained 

 by noting that in tardy regeneration one of the minor l.s.c. had 

 time to regenerate something like a normal primordium site with 

 major stripe contrast. When a number of aboral halves were 

 grafted together with a single normal primordium site, the latter 

 produced the sole initial anlage and only one set of mouthparts 

 was regenerated. In later reorganizations the minor l.s.c. had their 

 effect in multiple oral differentiation, and eventually the original 

 primordium site disappeared (Fig. 51 a). This decline of one 

 primordium site appears to have been by a shifting forward and 

 gradual absorption of the fine-line zone, but in most cases the same 



