14 THE BIOLOGY OF STENTOR 



When items of considerable size, like small rotifers or hypo- 

 trichs, fall into the oral pouch they are trapped by its partial 

 closure as already indicated by Johnson (1893) and Andrews (1946). 

 As I often observed, the rim of this cavity is independently con- 

 tractile and closes a widely opened pouch until only a narrow 

 orifice is left while the rest of the frontal field remains completely 

 expanded. Cilia from extensions of the ciliary rows in the frontal 

 field into the pouch cause the particles to spin around inside. 

 Schaeffer stated that there was less of this looping if the animals 

 were either hungry or well-fed, as if in the first case they were in 

 a hurry to ingest the food while in the second they would not 

 bother to test it. He therefore thought that the oral pouch is the 

 organ of food selection; but Dierks maintained that selection 

 occurs principally at the opening into the gullet and I am inclined 

 to agree with him from observation that particles are not rejected 

 until after they have reached and spun around for a moment in 

 this region. As Schaeffer noted, particles may be rejected at the 

 same time that others are being ingested, so that selection is indeed 

 precise and implies a fine coordination. Even after particles enter 

 the gullet reversal of the cilia there may eject undesirable items, 

 but once they pass to the lower end the cilia invariably carry them 

 inward, according to Dierks. 



Food is propelled in the gullet not only by specialized body 

 cilia but also by the spiral extension inward of the membranellar 

 band. The entire gullet seems to be formed by invagination and 

 extension of this band and of originally surface ectoplasm lying 

 adjacent, both spiralling inward. An orderly contraction of ecto- 

 plasmic myonemes thus carried into the gullet could therefore 

 produce the peristalsis observed by Dierks, which apparently 

 comes into play when large objects are swallowed. Dierks also 

 confirmed that Stentor is more selective of what it ingests as the 

 cell becomes replete. 



The pouch and gullet, like the cell surface in general, are 

 capable of great extension and contraction. In cannibalization they 

 open wide enough to accommodate a fellow stentor nearly as large 

 as the predator. Gelei (1925) therefore thought that the fine mesh- 

 work surrounding the gullet which he observed in sectioned 

 animals is to prevent tearing of this organelle when greatly 

 stretched. He also found that the force of closure of the oral 



