CHAPTER XIV 



ANALYSIS OF STENTOR THROUGH ITS 

 RESPONSE TO EXTERNAL AGENTS 



Various chemical and physical treatments of living stentors have 

 been used to reveal and analyze otherwise inaccessible aspects of 

 their structure and behavior. These studies are classified according 

 to objectives of the investigation, types of eflFects produced, or the 

 agent used. 



I. Action of the membranellar band 



To immediate observation, the most impressive activity of 

 attached stentors is the orderly beating of the large membranelles 

 in beautiful waves of metachronal rhythm. For the membranelles 

 do not all beat together in the same phase but in succession, so 

 that at any one instant membranelles in the eflFective beating stroke 

 are followed by others successively relaxed in the recovery stroke 

 and these are again followed by organelles in the effective stroke, 

 giving the impression of waves originating in the gullet and passing 

 along the membranellar band to its terminus. Hydrodynamically, 

 this type of beating is probably the most efficient, because groups 

 of cilia work together to move the water toward the mouth but this 

 action is distributed so that there is a continuous flow, whereas if 

 all membranelles beat in the same phase the medium would move 

 by starts and stops. 



The types of action of which the membranelles are capable and 

 the variables involved are shown diagrammatically in Fig. 67. 

 First, the membranelles may all be stopped and pointed forward 

 and somewhat inward, when stentor is swimming backward or 

 has momentarily ceased feeding (b). When they resume beating 

 they do so at first individually and at random, soon falling into 

 metachronal rhythm. Hence each membranelle is capable of 

 independent beating. The number of strokes per second is the 

 frequency of beating. Presumably the amplitude of the eflFective 



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