CHAPTER X 



THE PRIMORDIUM IN RELATION 

 TO THE STRIPE PATTERN 



We return now to the site of the primordium to learn what 

 pecuHarity this region may have that it should serve as the place 

 where the new feeding organelles always normally originate. 



I. Nature of the normal primordium site 



Schuberg in 1890 had already described a special geometry for 

 this area which he called the ramifying zone. There he noted 

 especially that the lateral striping does not run all the way to the 

 posterior pole and his figures clearly and correctly show that in 

 this region the granular stripes are the narrowest of any on the cell 

 and the ciliary rows correspondingly close together. Causin (1931) 

 and others have clearly seen and depicted these differences in the 

 striping but it is not uncommon to find pictures of Stentor which 

 completely ignore this distinction. That the oral primordium 

 always appears at a definite position on the cell was Schuberg's 

 main point. It soon became apparent that the narrow granular 

 stripes are found in the region posterior to the mouth because the 

 wide stripes to the left have been split to permit the interpolation 

 of new clear stripes with their kinetics and attendant structures. 

 The primordium site is thus also the region of stripe multiplication, 

 and indeed both processes run simultaneously during anlage 

 formation 



Morphologically, the ventral area may be characterized as the 

 place where the oldest and broadest granular stripes meet the 

 newest and narrowest in a locus of sharply contrasting stripe 

 widths. This asymmetry of the lateral striping is found in all 

 species of Stentor. That the kinetics are not equidistant in other 

 ciliates, and close together in the region of oral formation, may be 

 the case in some, though this is by no means obvious. In the related 

 Folliculina, Faure-Fremiet (1932) could find no ramifying zone 



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