ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 757 



an exceedingly rapid rectilinear movement. In this way it habitually 

 swims, turning on itself during its progress; but it can readily 

 deviate from the direct line when it has to avoid an obstacle. 



The other cilia which garnish the upper surface of the disk are 

 arranged in parallel lines, all curved in the same direction and 

 running from the margin of the peristome towards the mouth. In one 

 species Professor Fol counted twenty-four of these rows. The mouth 

 occupying an eccentric position, the rows which start from the 

 margin nearest to that aperture are of course much shorter than those 

 which start from the more distant margin (Figs. 7 and 8). There 

 are however only a few lines of cilia that reach the mouth, these 

 being the shorter ones, the others stop so as to leave the central part 

 of the disk naked (Fig. 8.) 



The cilia forming these rows are thick, short, slightly recurved, 

 scarcely attenuated at their free extremity, and only beat for moments. 

 Their length decreases regularly from the margin of the peristome 

 to the inner extremity of the row. 



Eetm-ning to the motor cilia and their relation to the cilia of the 

 disk, it is found that the margin of the peristome is not simply 

 rounded but rather denticulated, the teeth resembling those of an 

 ordinary saw, one side of which is very long and nearly a tangent to 

 the circumference, while the other is short and nearly follows the 

 radius. All the teeth are turned in the direction towards which the 

 rows of short thick cilia deviate ; and each of the rows corresponds 

 to one of the denticulations in such manner that it terminates at the 

 base of the longer side of the denticulation. 



The large motor cilia are imj)lanted upon the longer margin of 

 each denticulation. Hence they do not form a continuous cii-cular 

 or spiral line, but a broken line, the segments of which are only 

 simple continuations of the rows of short cilia. 



In other words all the cilia, whatever they may be, which garnish 

 the disk, are implanted in accordance with about twenty parallel 

 spiral lines. Each row commences tangentially to the margin of 

 the disk by a certain number of motor cilia, then curves towards the 

 centre, bearing short thick cilia, gradually diminishing from the 

 periphery towards the centre. 



The entrance to the mouth meets the surface of the disk obliquely, 

 the pharynx being directed towards the left, at the same time 

 gradually contracting (Figs. 7 and 8). By looking at the auimal 

 in profile (Fig. 7) it is easy to see that the pharynx is lodged in a 

 pouch-like lateral projection of the body of the Infusorian. This 

 projection is more strongly marked in certain species, and becomes 

 very striking in meagre individuals when placed exactly in profile. 

 A certain number of the rows of cilia of the disk (those, no doubt, 

 which start from the margin of the peristome nearest to the mouth) 

 may then be seen to descend into the pharynx, and there form a series 

 of nearly straight parallel lines composed of extremely fine cilia. 

 The actual margin of the mouth is furnished with tolerably stout 

 and long cilia which beat energetically ; but Professor Fol has not 

 succeeded in ascertaining precisely what relation may exist between 



