268 University of California Publications in Zoology [VOL. 20 



tion. According to his interpretation this "Querlinie" separates the 

 protoplasm of the cell body into two regions, the * * apical zone, ' ' which 

 I have described above as a thickening of the ectoplasm, and the rest 

 of the cell protoplasm. The extent of this * * Zwischenmembran " he 

 does not note, but his text figures (1 and 2) do not show it as extending 

 quite to the pellicle, but instead as stopping short of the pellicle at a 

 distance about equivalent to the thickness of the ectoplasm at that 

 point. This is significant in my interpretation of this region, namely, 

 that what appears as a continuous line or plane when viewed from 

 the side is in reality, as shown in cross-sections (pi. 27, figs. 6 and 7), 

 a set of diverging fibers. These fibers take origin from dark-staining 



oil 



cil. r. 



end. 



Fig. L. Portion of the peripheral region of a cross-section of Balantidium coli, 

 showing the structure of the ectoplasm and arrangement of cilia, somewhat dia- 

 grammatic. X 1500. b. ff., basal granule; oil., body-cilia; oil.r., ciliary rootlet; 

 end., endoplasm; gr. &., granular band of ectoplasm; hy. &., hyaline band of ecto- 

 plasm; pel., pellicle. 



enlargements on the longitudinal fibers in the wall of the gullet and, 

 diverging, pass peripherally until they turn posteriorly at the very 

 inner edge of the thin layer of ectoplasm which covers the remainder 

 of the body (pi. 28, figs. 9-12). Even in lateral view careful focusing 

 will often show that the apparent ' ' membrane ' ' is really discontinuous, 

 showing breaks and irregularities as one focuses on different levels 

 and hence can not be considered as a true membrane. The arrange- 

 ment of these fibers will be described more exactly under the discussion 

 of the neuromotor apparatus. 



The ectoplasm which constitutes a layer less than 3 microns in 

 thickness around the remainder of the periphery of the cell shows 

 a definite and somewhat complex structure. In tangential sections 

 of the surface, which are so thin that they do not include much of the 

 underlying endoplasm, one detects alternating light and dark longi- 

 tudinal spiral bands (gr.b., hy.b., fig. N). These bands are parallel 

 to the rows of cilia and very nearly equal in width. In cross-sections 

 (fig. L) they are seen to extend nearly, if not quite the full depth of 



