1922] McDonald: On Balantidium coli and Balantidium suis 271 



however, they turn toward the left, that is, in a counter-clockwise 

 direction when the animal is viewed from a point exactly in front. 

 They continue their spiral direction until almost to the posterior end 

 when they again follow a meridional path to their termination. In 

 passing the entire length of the body any single row of cilia twists to 

 the left approximately 120, or one-third the entire circumference. 

 Whether some rows terminate or become continuous with contiguous 

 rows before reaching the posterior tip of the animal, I have been 

 unable to determine, for both basal granules and granular bands 

 become very indistinct in this region even in the best preparations. 

 The number of rows was counted with difficulty in several cross- 

 sections from the equatorial regions of different animals, and it was 

 found to vary from about 60 in small individuals to 120 in larger ones. 

 No correlation between the variation in the number of rows of cilia 

 and the species of the animal could be determined, but this is possibly 

 due to the limitation of observation. 



Basal apparatus. The cilia perforate the pellicle and attach to 

 the basal granules which lie immediately underneath (fig. L). The 

 latter are small and apparently spherical or oval. They stain very 

 deeply black or blue with haematoxylin. In the living animal they 

 are readily emphasized by the use of neutral red, and less so by Janus 

 green. In preparations stained with Mallory's connective tissue stain 

 these granules show brilliantly red with the acid fuchsin, as do the 

 other parts of the neuromotor apparatus and also the micronucleus. 

 Longitudinally the granules are so closely placed that it is impossible 

 to observe whether they are actually connected by a fibre. Cross- 

 sections show that the cilia of one row have no transverse connection 

 by any sort of stainable fiber with those of the next row. The rows 

 of basal granules lie close beneath the depression in the pellicle in 

 the hyaline or bright band of the ectoplasm. A ciliary rootlet (cil. r., 

 figs. I and L) extends from each basal granule centrally toward the 

 endoplasm. It does not proceed in an exact radial line but rather 

 diagonally toward the right until it enters the granular band near 

 the inner surface of the latter. The ciliary rootlets in some cross- 

 sections appear to have an exactly radial direction. In such cases, 

 however, the granular band is somewhat diagonal in the opposite 

 direction. This variation is probably produced either by torsion of 

 the animal or by the direction of the effective beat of the cilia at the 

 instant of fixation. The diagonal direction of the rootlets is readily 

 detected in tangential sections. In focusing down through such a sec- 



