1914] Sharp: Diplodinium ecaudatum 87 



4. Every mobile territory is supplied by strands from the central 

 mass (motorium) and especially are the bases of the membranelles, 

 both dorsal and adoral, well supplied by these fibers. 



5. All parts connected by this neuromotor system act in perfect 

 co-ordination. For example, on being surrounded by an irritating 

 medium, mouth, oesophagus, and oral disk are retracted, not in the 

 direction of the motor strands, but posteriorly into the body, the 

 inner adoral and inner dorsal lips are shot forward completely en- 

 closing the adoral and dorsal membranelles (fig. D), the motion of 

 these membranelles and of the oral cilia is suspended, and for the 

 time being, the animal remains in an apparently inactive condition. 

 On being again surrounded by a favorable medium, however, the 

 cilia once more take up their activity, even while retracted within the 

 body. Finally the oral region is protruded, the inner adoral and 

 inner dorsal lips return to their original position, and the animal 

 exhibits all its former liveliness of motion. Not only do the two zones 

 of membranelles act in unison when the animal is swimming freely, 

 but during semi-quiescent periods as when the animal is feeding on 

 a mass of bacteria, the adoral membranelles and oral cilia may be 

 particularly active while the dorsal membranelles remain motionless 

 or only slightly active. Or again only a few of these membranelles 

 may be active while the others are entirely motionless, thus suggesting 

 the innervation of each single membranelle by a separate fiber. 



Not least in significance for this conception, is the fact that this 

 neuromotor apparatus is located in the most advantageous position 

 possible to function as a center of motor co-ordination in an animal 

 which is exceedingly active, exceedingly sensitive, and exceedingly 

 responsive to external stimuli, and one, moreover, which exhibits a high 

 degree of selective feeding. Also in this connection it is to be noted 

 that that portion of the animal which first comes in contact with new 

 media, viz., the operculum, is the most richly supplied with fibers 

 radiating from the motorium {op. f., figs. B, C, D ; pi. 6, figs. 13-15). 



A consideration of the location and the distribution of the opercular 

 fibers suggests the interesting question of the possibility of these 

 fibers having a sensory function. Such a view is not advanced to the 

 exclusion of other possible functions. If, however, these opercular 

 fibers do serve as conductors of sensory impulses, then their location 

 in the most anterior, most exposed portion of the body, is one of 

 advantage, especially when the membranelle zones are enclosed. Such 



