270 University of California Publicaiimis in Zoology [Vol. 20 



each end, which is comparable with the arrangement in Stentor, 

 though in the latter the narrowing must necessarily take place in the 

 posterior direction only. The above author mentions the branching 

 of stripes, but tliis does not occur in Balantidimn so far as I have been 

 able to determine. As the bands pass posteriorly, however, thej' 

 become less distinctly differentiated and are hard to follow, and it 

 might be that further study with more intensive stains would reveal 

 a union in the region of convergence at the posterior end. More recent 

 work has added to the number of Heterotrielia that show this sort of 

 differentiation of ectoplasm. Maier (1903) shows the striped nature 

 of this la.yer in Prorodan- and Spirosiomum, while Neresheimer (1903) 

 confirms the stracture found by Joluison ( 1893 ) in Stentor. Schuberg 

 (1887) also indicates a comparable plan of structure in Bursaria. 

 The granular ridges of ectoplasm between the furrows in which the 

 anal cirri are situated in Eiiplotes patella, discovered by Yocom 

 (1918), may be comparable with the bands which occur in Hetero- 

 tricha. 



Cilia. — The entire surface of Balantidium coli, with the exception 

 of the oral plug, is thickly beset with cilia {cil., ador. c, fig. I). These 

 are of two kinds, viz., those which make up the adoral row of cilia 

 and which measure from 8 to 12/* in length, and those covering the 

 body, which vary from 4 to 6ju. Those covering the apical cone, form 

 an intergradation between the two. On this surface the cilia which 

 occur immediatelj' posterior to the adoral row are only slightlj' shorter 

 and slightlj^ more slender than the adoral cilia themselves. Passing 

 posteriorly they gradually become shorter and less cirrus-like until 

 they reach the base of the apical cone. Thence posteriorly they retain 

 the uniform size. 



The body cilia are comparatively short and veiy slender. So small 

 are they in fact that to observe a single one is nearly impossible. In 

 slides prepared by the usual methods no stain remains in the cilia if 

 destaining is carried sufficiently far to differentiate other structures. 

 Iodine (Weigert's solution) gives a fairly satisfactory' stain for tem- 

 porary mounts. The arrangement of cilia may be determined most 

 readily by using a heavier stain and then observing the distribution 

 of basal granules. Neutral red proves very satisfactory for this pur- 

 pose. The cilia occur in longitudinal, slightly spiral rows, following 

 the grooves between the ridges in the pellicle. These rows originate 

 immediately posterior to the groove in which the adoral cilia are set 

 and for a very short distance pass almost meridionallj' ; very soon. 



