290 University of California Publications in Zoology [VOL. 20 



fibrillar portion of the apparatus common to all three forms is the 

 strand connecting the motorium with all of the* adoral cilia or mem- 

 branelles, as the case may be. Finally, the system, in all cases, shows 

 an affinity for acid fuchsin. 



The circumoesophageal ring present in Diplodinium is represented 

 in Balanticbium by the circumoesophageal fiber running through the 

 oral plug. The oral plug forms the wall of the greater part of the 

 oesophagus, and the fiber lies very close to the oesophageal surface. 

 From this fiber there are given off fibers which pass both anteriorly 

 and posteriorly in the mass of the oral plug. These fibers are strik- 

 ingly similar in location to the oesophageal fibers, described by Sharp 

 (1914) in the wall of the oesophagus of Diplodinium and believed by 

 him to arise from the circumoesophageal ring. Sharp points out that 

 these fibers approach very close to the micronucleus though there was 

 no demonstrable connection with it. In Balantidium this possibility 

 is precluded by the shortness of the oesophagus which in no case 

 extends inward to a point anywhere near the micronucleus. At times 

 when the organism is viewed from the proper angle, the ciliary root- 

 lets of the adoral cilia may have the appearance of ending in the 

 proximity of the micronucleus and suggesting a connection with it. 

 No such connection exists, however, as may be readily demonstrated 

 in large numbers of whole mounts and still better in sections where 

 these rootlets may be traced far posterior to the micronucleus, passing 

 it some considerable distance away. In the vegetative phase, it is 

 certain that no structural connection exists between any part of the 

 neuromotor apparatus and the micronucleus. 



Of the three neuromotor systems of ciliates here considered, that 

 of Balantidium is clearly the least centralized, though none the less 

 a unified structure. In Diplodinium all motor organelles connect 

 directly with the motorium, and in Euplotes the same is true of all 

 except the marginal cirri which have no connection whatever, whereas 

 in Balantidium only the adoral cilia have direct connection with the 

 motorium while the cilia of the apical cone (and those of the body, 

 too, if they have any connection whatever) are connected with it only 

 indirectly through the radial fibers and the rootlets of the adoral cilia. 

 This lesser degree of centralization of the neuromotor apparatus may 

 perhaps be explained by the lesser degree of specialization of locomotor 

 organelles. Whereas in Diplodinium the body is devoid of cilia and 

 the dorsal and adoral zones of membranelles are the sole motor organ- 

 elles, and in Euplotes the locomotor organelles are restricted to the 

 cytostomal membranelles and a few cirri on the ventral surface, in 



