l8o THE BIOLOGY OF STENTOR 



and described the pigmented stripes as not being graded in width. 

 Yet in Paramecium the oral anlage does appear near the junction 

 of two differently patterned areas (Ehret and Powers, 1959). 



2. Production of supernumerary primordia 



If the crucial feature of the primordium site lies in something 

 correlated with the visible appearance of contrast between wide 

 and narrow granular stripes, then it should be possible to elicit 

 primordium formations in atypical loci by creating such areas of 

 contrast by operative manipulation. This has proved to be the case, 

 for a wide spectrum of experiments has shown that primordia 

 appear wherever and however wide- and narrow-stripe areas of 

 the ectoplasm come together to create a locus of sharp contrast in 

 stripe widths (Tartar, 1956a, b, c). 



First it was shown that the primordium site need not be in the 

 normal position in order to produce an anlage and that a single 

 animal or simple coeruleus graft complex can produce and develop 

 more than one oral primordium. Thus when an extra primordium 

 site cut from one stentor, and not necessarily carrying any macro- 

 nuclear nodes, was grafted into the back of another animal and 

 regeneration induced by excising the mouthparts, anlagen appeared 

 simultaneously in both normal and ectopic sites and a doublet or 

 bistomial stentor was always produced (Fig. 46A). It was then 

 found that when only the sector characterized by fine pigment 

 stripes in which the primordium first appears at stage i is 

 implanted, an extra primordium still appears and it forms on the 

 side of the graft where the narrowest stripes of the implant lie 

 adjacent to wide stripes of the host (b). If such a patch was reversed 

 and implanted heteropolar the extra primordium then appeared 

 on the other side where the contrast in stripe widths was now the 

 greatest (c). This anlage soon assumed the polarity of the host, but 

 on forming the gullet the posterior end curled to the left instead 

 of the right and an incompletely developed set of mouthparts of 

 reversed asymmetry was produced. In the controls in which sectors 

 bearing wide stripes were grafted into the back, or wide stripe 

 area, no extra primordium formation occurred. 



Taken together, these experiments are enlightening. The suture 

 as such, produced by grafting, is not the cause of anlagen forma- 

 tion. Instead oral differentiation occurs onlv if and where an area 



