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 motionless, Ave 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 alternate 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 



Q 



