CILIATE FIBRILLAR SYSTEMS 247 



of the adoral zone, and other fibrils which appear to end bhndly in the 

 endoplasm of the ventral lobe. Anteriorly the fibrils of the frontal field 

 tend to converge and end very obliquely on the adoral fbril. 



No pellicular pattern was demonstrated by any of the silver methods, 

 but they did show the longitudinal fibrils connecting the cilia. 



Methods 



Fixatives: Schaudinn's, Bouin's and Flemming's. 



Stains: Iron-haematoxylin, Mallory's triple. 



Silver method : Yabrotf's modiiication of Da Fane's. 



Metopus circumlahens (Lucas, 1934). — The motorium of Met opus 

 circiiuilabens lies posterior to the cytostome. From its left side it gives rise 

 to a pair of ventral adoral fibrils which follow the peristomal curvature 

 outward to the oral margin and there end in a sort of arborization. Each 

 row of peristomal membranelles arises immediately in contact with a con- 

 nective between these two fibrils. A dorsal adoral fibril extends from the 

 right side of the motorium. At slightly irregular intervals is gives rise 

 to from ten to twenty heavy connectives, which may partially fuse in 

 pairs as they curve beneath the dorsal wall of the peristome to its left 

 side. There they turn ventrad and unite with the ventral adoral fibers. 

 A fibrillar pharyngeal strand arises from the posterior end of the moto- 

 rium. Its course varies in different organisms, but it usually lies along the 

 right lateral wall of the organism to the right of the cytopharynx. Near 

 the posterior end of the latter structure it forms a large spiral coil. 



The entire body surface, except the right lateral margin, is covered 

 with rows of cilia. Longitudinal ciliary fibrils are present, but no com- 

 missural fibrils were observed. Each basal body in the most dorsal of the 

 five rows of the crest cilia gives rise to rootlets which end freely in the 

 cytoplasm. A relation between these peripheral fibrils and the fibrils of 

 the motorium seems to be suggested by the numerous fine branches which 

 arise from the ventral adoral fibrils. These extend indefinitely into the 

 cytoplasm toward the longitudinal ciliary rows of the ventral surface. 



In view of the contrastingly striking and obvious specialization in the 

 fibrillar structure of the neuromotor system about the peristomal, pharyngeal, 

 and central endoplasmic regions of the cell, one is inclined to believe that 

 the neuromotor system of this ciliate is vitally, though not exclusively, con- 

 cerned in the conductile functions related to the metabolic activities of the 

 organism. It is possible that, because they are located within the mobile 



