1922] McDonald: On Balantidium coli and Balantidium suis 269 



the ectoplasm. As one follows these bands (or "stripes," as they are 

 named by Johnson (1893, in his work on 8 tent or) anteriorly they seem 

 to lose their distinctness when they become continuous with the apical 

 cone. In some individuals, however, one can follow them some distance 

 into this cone, but never is there the same degree of differentiation of 

 the two areas in this region. 



In the living animals, which are often quite opaque due to inclu- 

 sions, it is nearly impossible to distinguish these longitudinal light and 

 dark bands. With neutral red the dark or granular band stains 

 faintly. With the haematoxylin stains used in thin sections of fixed 

 material the dark band seemed to be finely granular in fundamental 

 structure. The granularity in this case must be determined largely 

 by the general appearance and stainability, for the individual granules 

 are so small as to defy identification. There is no indication, however, 

 of alveolar structure, so that the term granular is probably the more 

 applicable and will be used to distinguish this from the light band. 

 The latter takes only faintly the stains used and seems hyaline in 

 structure. The granular bands lie directly beneath the ridges in the 

 cuticle which occur between the rows of cilia. Or more correctly, 

 the ridges on the surface of the animal are produced by the projection 

 of these granular bands outwardly beyond the hyaline bands. These 

 latter are directly beneath the grooves of the surface where the cilia 

 pass through the cuticle and attach with the basal granules which lie 

 in longitudinal rows; a single row in each hyaline band. The ciliary 

 rootlets (cil. r., figs. I and L) extending in from the basal granules 

 proceed diagonally inward and pass into the interior margin of the 

 granular band. 



Stein as early as 1876 pointed out these alternating dark and light 

 stripes in Stentor. To the granular and bright stripes, Biitschli 

 (1889) gave the names ' ' Riffenstreif en " and " Zwischenstreif en, " 

 respectively. Johnson (1893) gives a careful description of these 

 bands as they occur in Stentor coeruleus. He notes that they vary 

 greatly in width, and this is true in Balantidium; but both bands are 

 much narrower than in Stentor, the combined width of the two not 

 exceeding two microns. In Stentor coeruleus Johnson (1893) gives 

 the width of the granular band as 22/x and that of the bright band 

 as 7/x, these measurements being taken just under the adoral zone. It 

 is interesting to note that in Balantidium coli the granular band is also 

 slightly wider than the bright band. These bands become narrower 

 from the region of the greatest circumference of the animals toward 



