1922] McDonald: On Balantidium coli and Balantidiutn siois 277 



clearlj' the ventral lip of the peristome; the seeoud line was identical 

 with the deep staining motoriuni (fig. I) in the forms which I studied, 

 and the most posterior line seemed identical with the ring of enlarge- 

 ments on the rootlets of the adoral cilia which lie close about the 

 oesophagus. The margin of the peristome is slightlj- raised, forming 

 a ridge or lip. This ridge is most pronounced from the midventral 

 point, dorsal along the right margin of the eytostome, but as it pro- 

 ceeds around it becomes rather inconspicuous and wholly disappears 

 on the left side. Thus the cj-tostome has the appearance of opening 

 under a ledge, the ledge formed by the lip of the right side. 



The peristome is delimited by an almost complete spiral circlet of 

 cilia, the adoral cilia {ad. cil., fig. I). The exact point of origin of 

 the row is hard to determine but it is approximately at the ventral 

 edge of the peristome, i.e., on the ventral lip of the eytostome. From 

 here it proceeds in a sort of gi'oove, along the right margin, around 

 the dorsal margin, and down the left margin of the peristome. A 

 short distance in advance of the ventral point, the row of adoral cilia 

 turns into the eytostome and continues in a spiral course down the 

 oesophagus ; entering at the left dorsal side and ending in the ventral 

 wall about halfway down. Thus these cilia in their entire course make 

 one complete left-hand spiral, beginning on the ventral lip, passing 

 around the peristome and down the oesophagus, terminating in its 

 ventral wall. 



Over the lip of the eytostome between the point where the adoral 

 cilia turn into the oesophagus and the midventral point where this 

 row of cilia has its origin, the longitudinal rows of body cilia turn in. 

 Each of these rows, of which there are ten or twelve altogether, con- 

 tinues down the oesophagus until it meets the row of adoral cilia. 

 Since this latter enters spirally, there is a ciliated patch on the ventral 

 wall of the funnel-shaped oesophagus which is roughly the shape of a 

 right triangle, the base of which is the lip of the eytostome. The 

 hypotenuse is the row of adoral cilia which makes an acute angle with 

 the longitudinal row of bodj' cilia which enters in the mid line and 

 which represents the third side of the triangle. 



The adoral cilia, except where they lie within the oesophagus, are 

 completely separate each from the other. This is easily verified by 

 watching their action especially in a disintegrating animal, or one 

 cooled to slow up ciliary movement, under which condition coordina- 

 tion is frequently interrupted, and a single cilium will be seen acting 

 independently of its neighbor. Additional evidence is to be found in 



