WHEEL-BEARERS. 225 



and this approximation increases the farther the flexure 

 proceeds, it follows that at the bottom of each wave the 

 tips of the cilia overlap their successors, while the spaces 

 perpendicularly above their bases are left more open by 

 the removal of their points. 



Hence, in microscopical observation of ciliated animals, 

 though the individual cilia are too minute to be discerned 

 while stilj., we can readily discern the increased density 

 (and therefore opacity) of the bottom of a wave, contrasted 

 with the increased openness (and therefore clearness) of 

 the summit. So that the optical effect is that of an alter- 

 nate succession of dark and light spots blending into each 

 other. 



But as no cilium in the series is for two successive 

 moments in the same degree of flexure, and as both it and 

 all its predecessors and successors are ever urging on their 

 perfectly timed and regulated course, the waves are never 

 fixed, but always gliding on with a swift but beautifully 

 even rapidity. And as it is with the waves, so it is with 

 their optical effect upon the eye ; the black and white 

 spots, or rather the black spots with blank intervals, 

 appear to be constantly chasing each other in ceaseless 

 race. 



You are then prepared to take a peep at this beautiful 

 Brachionus pala. A cup of elegant form, swelling at the 

 sides and narrowing a little at the mouth, has one side of 

 its rim furnished with four spines, the middle pair of 

 which are very slender, sharp, and needle-like; the other 

 side of the rim is undulated, but not toothed. The bottom 

 of the cup terminates in two broad, blunted points — when 

 seen directly in front ; but a lateral view considerably 

 modifies the whole form. Then you see that the back of 

 the cup is much more swollen, the belly-edge being nearly 

 straight, and that this latter descends much lower than 

 the dorsal line, the bottom being as it were cut away 

 obliquely and slightly hollowed. Between the two bottom 



Q 



