30 THE BIOLOGY OF STENTOR 



field, forming what Johnson called the buccal fold. Oralward the 

 wall of the pouch lies against the body ectoplasm, forming a thin 

 wall which is apparently what Johnson called the " velum ". 

 The membranellar margin of this wall bends inward, producing 

 the groove which Schuberg emphasized, and is capable, by 

 independent contraction, of increasing this over-hang or nearly 

 closing off the cavity below. It was Schuberg who first pointed out 

 that the oral or buccal pouch is not a part of the gullet but only a 

 modification of the frontal field, which later experiments confirmed 

 (see p. 172). 



(c) Membranellar band 



On first inspection membranelles appear to be merely large cilia, 

 and so they seemed to Stein (1867) and Simroth (1876); but Sterki 

 (1878) first noted that they are flat plates. Each lamella is formed 

 by many cilia clinging together in a sheet, presumably by the inter- 

 locking, as in the barbules of a feather, of lateral spurs recently 

 demonstrated through electron microscopy by Randall and 

 Jackson (1958). The same occurs in the formation of cirri in hypo- 

 trichs (Roth, 1956). All students had agreed that each membranelle 

 in stentors was made up of 2 rows of cilia and I found the same 

 in silver-stained polymorphus. It is therefore surprising that 

 Randall and Jackson describe from clear photographs triple rows 

 for the same species, except in the mouth region. This discrepancy 

 will have to be resolved. It is possible that strains could differ in 

 this respect and if so the number of rows could be an important 

 genetic character. In the ciliate Oxytricha membranelles are com- 

 posed of 3 rows of cilia (E. E. Lund, 1935). 



The row of membranelles is held together by some sort of band 

 or fibers at the level of the ciliary bases, and when shed in salt 

 solutions the membranelles do not fall apart but come off as a 

 continuous ribbon (Tartar, 1957a). Schuberg thought this union 

 was accomplished by thickened pellicle; Schroder by a special 

 meshwork or membrane. Dierks saw a fiber (of coordinating 

 function he supposed) connecting the membranelles at this level, 

 and such connectives are clear in the electronmicrographs of 

 Randall and Jackson but afford no indication of whether the 

 fibers are supportive, contractile, or coordinating. If isolated by 

 crushing, Moxon (1869) saw in the membranellar band "tremulous 



