FORM AND FUNCTION IN STENTOR 9 



of a new food vacuole and then close behind it as the vacuole is 

 pinched off into the interior. But vacuolar walls can arise de novo 

 as is seen when active rotifers are ingested and thrash around 

 inside the cell but are later re-encapsulated and digested. 



In feeding, the membranellar band by coordinated beating 

 creates a powerful vortex which draws in particulate food organ- 

 isms, large or small. Impinging on the frontal field, particles are 

 moved by its cilia toward the oral pouch in which they are trapped 

 and concentrated, whirling around within the cavity. In this region 

 the food is apparently tested. If undesirable or in excess, particles 

 are then ejected over the outer rim of the oral pouch and carried 

 toward the base of the animal, away from the feeding vortex, by 

 the backward-beating lateral body cilia. If to be ingested, the food 

 is passed down the gullet by reason of its ciliated lining and is 

 further concentrated while peristalsis of the gullet forces the 

 material into the interior. 



After digestion the residue in the food vacuole is cast out 

 through the left anterior wall of the cell below the pulsating con- 

 tractile vacuole. Especially when the stentor has been feeding on 

 tiny flagellates, many exhausted vacuoles accumulate and fuse in 

 this region, forming a very large bolas which requires about one 

 minute to be voided. Whether there is a permanent anal opening 

 or cytopyge may still be questioned. 



On the other hand, the exit of the contractile vacuole is visibly 

 persistent. Moxon (1869) observed openings in the broad granular 

 stripes exterior to the contractile vacuole which is always located 

 in the anterior left side of the cell. These openings are evident in 

 pigmented coeruleus as clear spots. One, at least, of these openings 

 expands noticeably when the contractile vacuole is voided, 

 assuring their identification. 



Larger species of Stentor have a moniliform macronucleus 

 composed of many nodes lying within a common nuclear mem- 

 brane. This nucleus lies underneath the ectoplasm and is deployed 

 in a characteristic way as shown in the illustration. Adherent to 

 the macronuclear nodes or nearby are many micronuclei. Smaller 

 species show a single compact macronucleus; and micronuclei, 

 which are very tiny in stentors, have not been seen in all species. 



Endoplasm fills the interior of the cell and is in irregular 

 cyclosis, possibly because extension and contraction itself pro- 



