FORM AND FUNCTION IN STENTOR 7 



In pipetting animals from the sides of a vessel the holdfasts are 

 often torn off because of their firm adherence. Yet stentors can 

 release their hold at will under favorable conditions in order to 

 search for a better environment. Thus in unfed cultures many 

 animals will be found on the move as if searching for food. 



Some stentors form cases and are still more sedentary. Jennings 

 (1902) described how roeseli seemed to explore the substratum with 

 its anterior end and when a likely spot was found the tail bent over 

 and attached. Then mucous was secreted over the posterior half 

 of the body while the animal moved backward and forward on its 

 side for about two minutes as it secreted an elongated cylinder. 

 The tube was later compacted somewhat by subsequent contrac- 

 tions of the stentor. 



In describing the feeding organelles at the anterior end we shall 

 use the simplest and most unambiguous terms. Confusion and 

 synonymy have arisen in the past largely from unjustified attempts 

 to homologize these organelles with the upper parts of the human 

 alimentary canal, with the result that stentor should have both a 

 pharynx and an esophagus. There is said to be a buccal or cheek 

 cavity, yet what is called the mouth or cytostome does not in fact 

 open into this cavity but is homologous with the anterior pyloric 

 sphincter. The membranellar band is usually called the peristome, 

 but it does not encircle the cytostome, and the term "peristome" 

 was originally used to designate a special fold generally running 

 alongside this band (see Johnson, 1893). Regardless of more 

 precise designations, however, it will be convenient at times to 

 refer to the entire set of feeding organelles at the anterior end as 

 the '*head"; to the oral pouch, gullet, and cytostome as the 

 '* mouthparts " ; and to the holdfast as the " foot ". 



The anterior end or frontal field is covered with alternating 

 clear and granular stripes the same as the lateral body wall from 

 which it is derived (Fig. i). Being newly formed, the granular 

 stripes there are narrow and the clear bands with their ciliary rows 

 or kinetics are close together. Bordering and almost completely 

 enclosing the frontal field is a band of membranelles which nor- 

 mally spirals always in one direction as shown in the figure. 

 Fully extended, the frontal field and bordering membranelles 

 take the form of a broad funnel. At the left side, in most stentors 

 the frontal field dips down sharply with its striping into an oral 



