1922] McDonald: On Balantidium coli and Balantidium suis 285 



oesophageal fiber, beginning and ending in the motorium and giving 

 off branches as it passes through the oral plug; (3) a fiber connecting 

 the adoral cilia and the cytostomal membranelles with the motorium ; 

 (4) the adoral ciliary rootlets passing posteriorly from the basal 

 granules of the adoral cilia, each bearing an enlargement where it 

 passes from ectoplasm into endoplasm, and finally ending without 

 attachment in the endoplasm of the cell; (5) the radial fibers taking 

 origin from the enlargements of the adoral ciliary rootlets and passing 

 radially to the ectoplasmic layer where they turn posteriorly into the 

 granular band. 



The motorium (mot., figs. I and J) when viewed in ventral aspect 

 has somewhat the appearance of a reversed letter J. It lies within 

 the ectoplasm of the apical cone, close to the ventral and right walls 

 of the oesophagus. The part of the motorium corresponding to the 

 vertical shaft of the J lies along the right wall of the oesophagus, and 

 its anterior terminus is situated just inside and slightly dorsal from 

 the point of origin of the right lip of the cytostome. The curved end 

 of the J is posterior and passes ventrally and anteriorly around the 

 oesophagus and ends close to the inner termination of the rows of 

 adoral cilia. In the middle region a sharp slit-like constriction is often 

 very conspicuous. It is with the part of the motorium anterior to this 

 constriction, that the circumoesophageal fiber and the adoral ciliary 

 fiber have their origin. The portion posterior to this constriction is 

 quite variable both in size and in stainability. This variation is very 

 suggestive of the behavior of the parabasal body of certain flagellates 

 as described by Kofoid and McCulloch (1916), Swezy (1916), Kofoid 

 and Swezy (1919). These authors have shown that the parabasal body 

 is not kinetic in function but instead is a reserve or reservoir of 

 material easily transformed into energy, which reservoir fluctuates 

 according to the physiological condition of the animal. No direct 

 evidence can here be advanced establishing such a function for this 

 posterior portion of the motorium, but the fact of its fluctuation in 

 volume and its variation in chemical nature (as shown by stains) 

 would lead one to suspect that such an interpretation is correct. 



The oircumoesophag&al fiber (dr. oes. /., figs. I and J) takes origin 

 from the anterior extremity of the motorium and passes into the oral 

 plug. Its course is very close to the inner, i.e., oesophageal, surface 

 of the plug. It encircles the oesophagus completely but in the mem- 

 branellar area it becomes very hard to follow. Certain sections (pi. 27, 

 fig. 3), however, seem to show that it unites again with the motorium. 

 It is not a smooth fiber but bears irregular enlargements from which 



