1922] McDonald: On Balantidium coli and Balantidium suis 289 



motorium is a somewhat bilobed mass and lies in the ectoplasm at 

 the anterior end of the organism close to the right anterior corner of 

 the triangular cytostome. From the left end of the motorium five 

 main longitudinal fibers pass posteriorly, diverging slightly, and each 

 joins with one of the five anal cirri. The exact relation of thes^ fibers 

 to the basal plates of anal cirri has been very carefully determined 

 by Taylor (1920). Leaving the right end of the motorium a fiber 

 passes to the membranelles of the adoral zone. Directly connected 

 with this fiber is the "sensory structure" of the anterior lip. Lastly, 

 there are dissociated fibers in connection with the frontal, ventral, and 

 marginal cirri. In Euplotes, as in Diplodinium, all parts of the 

 neuromotor apparatus as well as the micronucleus stain brilliant red 

 with acid fuchsin. 



For facilitating comparison, it might be well to summarize briefly 

 the neuromotor apparatus of Balantidium coli, as described above. 

 It consists in this organism of five distinct divisions. The motorium 

 is a J-shaped mass situated in the thickened ectoplasm of the anterior 

 end of the animal close to the cytostome and oesophagus. From it 

 arises the circumoesophageal fiber, which gives off branches to the 

 oral plug. A second fiber takes its origin from the motorium and 

 connects with the basal granules of the adoral cilia. The adoral ciliary 

 rootlets pass inward from the basal granules of the adoral cilia, and 

 may extend well into the posterior third of the cell. The radial fibers 

 take their origin from enlargements of the adoral ciliary rootlets, 

 at the point where they enter the endoplasm. They pass outward 

 radially, making connection with the ciliary rootlets of the cilia of 

 the apical cone, and at the periphery turn posteriorly and cannot 

 be traced farther in the granular bands of the ectoplasm. As in the 

 previous forms just summarized, the neuromotor apparatus as well as 

 the micronucleus of Balantidium coli is selective for acid fuchsin. 



Of the three examples of neuromotor systems so far fully worked 

 out and described, each represents a different order of the class 

 Ciliata: Diplodinium being of the order Oligotricha; Euplotes being 

 of the order Hypotricha ; and Balantidium being of the order Hetero- 

 tricha. Yet in spite of the diversity of forms there is a remarkable 

 similarity in the neuromotor system. The presence of a motorium is 

 common to all three. In each of the three organisms it is located at 

 the anterior end of the animal and lies wholly within the ectoplasm 

 near the cytostome. By means of fibers it is connected with a part 

 or all of the motor organelles of the animal. Another feature of the 



