CHAPTER IV 



FINE STRUCTURE 



Bearing in mind our general survey of the morphology of Stentor, 

 we can now probe the intimate construction of its parts as the 

 structural basis of its living functions and behaviour. Every detail 

 we learn only increases our wonder that stentors are capable of 

 such remarkable feats of regeneration and reconstruction after the 

 cutting needle comes crashing through these complex and highly 

 organized cell differentiations. 



I. Feeding organelles 



The differentiations at the anterior end of stentor are formed 

 in a few hours from an oral primordium in the most dramatic act 

 of cytoplasmic elaboration shown by this animal. A band of 

 membranelles develops on the side of the cell and carves out an 

 area of the ventral striping to the right which it carries forward to 

 the anterior end, as the posterior terminus of the band invaginates 

 to form the gullet and the adjacent part of the isolated striping 

 indents to produce the oral pouch. An important consideration 

 is whether all growth and elaboration of oral parts occurs only 

 through primordium development. If so, the size and number of 

 membranelles should not increase thereafter, the gullet would not 

 increase in resting diameter or length, and the number of stripes 

 in the frontal field should remain the same after oral differentiation 

 regardless of increase in cell volume through growth. Indications 

 that this may be the case are found in the fact that adoral bands 

 and gullets abbreviated by cutting do not grow out again in situ 

 but initiate regeneration of a whole new set of feeding organelles. 

 But in regard to decrease in these structures through dedifferentia- 

 tion and resorption the situation is entirely different, for the 

 membranellar band and gullet can shorten in situ (see p. 125). 



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