CHAPTER II 



FORM AND FUNCTION IN STENTOR 



To BECOME acquainted with Stentor we begin with an account of 

 those features of the organism which are open to simple observa- 

 tion, emphasizing S. coeruleus which, because of its commonness 

 and reveahng pigmentation, has been the favored type for study; 

 but there is no reason to beheve that even httle-known species 

 differ fundamentally in basic Bauplan or manner of living. 



Several of the early investigators were impressed by what 

 seemed to them to be the great variability in form of stentors, as 

 the species name polymorphus and multiformis imply ; but the form 

 of Stentor is no more indefinite than that of an earthworm merely 

 because it extends and contracts. The shape of Stentor is simply 

 that of a cone capable of extension or of contraction into a sphere. 

 Attachment is by the point of the cone, a small enough area to 

 permit voluntary release; while the feeding organelles are at the 

 broad end where they can most effectively produce a vortex 

 bringing particulate food to the animal from a large region of the 

 medium which lies beyond it like an imaginary extension of the 

 cone. Set free and swimming, the shape of the cell under what 

 seems to be minimum tension is, as Merton (1932) remarked, 

 that of a gently rounded cone. Shortening of contractile elements 

 pulls the cone into a sphere, and extension is the result of elasticity, 

 pulling by the feeding membranelles, and possibly transverse 

 contraction. 



The surface is covered by alternating longitudinal stripes of 

 two kinds: bands of granules, often colored, forming stripes which 

 increase in width in an orderly way around the cell and, between 

 these, clear stripes of relatively constant width which bear the 

 rows of body cilia as well as a complex of fibers probably respon- 

 sible for longitudinal contraction and ciliary coordination (Fig. i). 

 To accommodate for the decreasing cross-section of the cone the 

 granular stripes taper near the apex and some of both kinds of 



