252 CILIATE FIBRILLAR SYSTEMS 



Diplodinium ruedimn (Rees, 1931). — The structure of D. medium is 

 compared with D. ecaudatum as described by Sharp. The disagreement 

 between Rees's interpretation and the interpretation of Sharp has to do 

 primarily with the ectoplasmic layer directly under the pellicle, except 

 in the region of the adoral lip and the inner boundary layer of the ecto- 

 plasm. In D. medium this layer, according to Rees, is more prominent 

 than in D, ecaudatum and consists, instead of fine alveoli, of an inter- 

 woven network, or complex system of fibrils. Serial cross and longitudi- 

 nal sections, 3 pi. in thickness, made it possible to trace the ectoplasmic 

 layers. 



Cross sections of D. medium show a fold of this middle layer of the 

 ectoplasm which corresponds in its position to Sharp's motorium. Further- 

 more, the esophageal ring described by Sharp is interpreted as section 

 of the inner boundary layer of ectoplasm. The fibers connecting the 

 mortorium with the membranelles and esophagus could not be differ- 

 entiated. 



The ciliary rootlets are attached to membranes composed of sheets of 

 the fused middle and inner layers of ectoplasm, which in turn are at- 

 tached to the fibrillar system of the ectoplasmic layers The structures are 

 membranes, according to Rees, because "one or the other of them occurs 

 in all longitudinal and oblique sections, whether cut with reference to 

 the parasagittal plane or to a plane at right angle or at any other angle 

 to it." The esophageal tractor strands are considered to be a part of the 

 ectoplasmic network of fibrils. The membranes, instead of strands, are 

 believed by Rees to function in the retraction of the adoral and the dorsal 

 cilia. 



The occurrence of fine fibrillae in the non-ciliated ectoplasm of Diplodinium 

 is of interest in connection with other papers on the neuromotor system. It is 

 obvious that in the latter ciliate the fibrillae of the ectoplasmic layers have no 

 relationship to a neuromotor system. 



Methods 



Fixatives: Not listed. 



Stains: Iron-haematoxylin, Zirkle's N-butyl alcohol method of dehydration. 



Diplodinium Schbg. (Kofoid and MacLennan, 1932). — In addition 

 to the neuromotor apparatus as described by Sharp (1914) for D. ecauda- 

 tum and incidentally confirmed in this systematic investigation, a fibrillar 



