Prof. H. Fol on the Family Tintinnodea. 239 



degree. The undulation is propagated from right to left, the 

 observer being supposed to be placed in the axis of the animal ; 

 so that one would imagine he saw a toothed wheel turning in 

 the direction indicated (PI. XVII. figs. 2, 3, and 4)._ Are 

 these cilia implanted upon a single circular or spiral line, as 

 Stein supposes ? or do they form a broken line ? To solve 

 this question we may begin by examining the arrangement of 

 the other cilia which garnish the upper surface of the disk. 



These cilia are arranged in parallel lines, all curved in the 

 same direction (fig. 3) and running from the margin of 

 the disk, or peristome, towards the mouth. In one species I 

 have counted twenty-four of these rows. The mouth occu- 

 pying an exceutric 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 (see 

 figs. 2 and 3) ; the others are of intermediate length. There 

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

 entrance of the mouth ; and these are precisely the shortest 

 ones. The others stop so as to leave the central part of the 

 disk naked (tig. 3). 



All the rows of which I have just been speaking are formed 

 of thick, short, slightly recurved cilia, scarcely attenuated at 

 their free extremity, and only beating for moments. Their 

 length decreases regularly from the margin of the peristome, 

 which bears the thickest and longest, to the inner extremity 

 of the row, which is formed of much shorter and more slender 

 cilia (see figs. 2 and 3) . The shortest rows, which occupy the 

 buccal margin, are also those the cilia of which are shortest on 

 the average. 



Let us now return to the motor cilia, to ascertain what 

 relation they may present to the cilia of the disk. And, in 

 the first place, if we carefully examine the margin of the 

 peristome from the upper surface, leaving out of consideration 

 the cilia with which it is furnished, we shall notice that this 

 margin is not simply rounded, but rather denticulated. The 

 teeth resemble those of an ordinary saw ; that is to say, each 

 tooth is bounded by two lines, one of which is very long and 

 nearly a tangent to the circumference, while the other is short 

 and nearly follows the direction of a radius. It is unnecessary 

 to say that all the teeth are turned in the same direction. 

 Now this direction is precisely that towards which the rows 

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

 to one of the denticulations of the margin, in such a manner 

 that it terminates at the base of the longer side of the denti- 

 culation, or that which forms a tangent to the margin of the 

 disk. 



