436 EOTIFEEA. 



(1127.) Such being, as we conceive, the nature of the ciliary motion, 

 we will proceed to examine the uses to which it is made subservient in 

 the class of animals under consideration. A very slight examination of 

 one of these creatures under the microscope will show that the cilia 

 answer a double purpose : if the Rotifer fixes itself to some stationary 

 object by means of the anal forceps, the ciliary action, by producing 

 currents in the water all directed towards the oral orifice, ensures a 

 copious supply of food, by hurrying to the mouth whatever minute 

 aliment may be brought within the range of the vortex thus caused ; or, 

 on the other hand, if the animal disengages itself from the substance 

 to which it held by its curious anchor, the wheels, acting upon the 

 principle of the paddles of a steamboat, carry it rapidly along with an 

 equable and gliding movement. 



(1128.) The whole ciliary apparatus, when not in use, is retracted 

 within the orifice of the shell, and lodged in a kind of sheath formed 

 for it by the inversion of the tegumentary membrane. The muscular 

 fasciculi by which this is effected are very conspicuous; they arise 

 from the lining membrane of the shell, and run in distinct fasciculi in 

 a longitudinal direction, to be inserted into the lobules whereon the cilia 

 are arranged (fig. 230, m m). 



(1129.) But, besides these retractor muscles, other fasciculi of mus- 

 cular fibres are distinctly seen to run transversely, crossing the former 

 at right angles : these are, most probably, the agents provided for the 

 extrusion of the wheel-like apparatus ; for, arising, as they do, from the 

 inner membrane of the hard integument, they will, by their contraction, 

 compress the fluid in which the viscera float, and, forcing it outward 



then returning with the same rapidity of motion to its first condition, A B, repeating 

 continually similar movements in both directions. Now, as the other cilia of the 

 series only commence this movement one after the other, each being in advance of 

 the preceding one on the left hand by a fourteenth part of the space occupied by the 

 entire wave, and the same distance from that which succeeds it on the right hand, at 

 every fourteenth interval the cilia present themselves in the same state of flexure, 

 and a row of cilia in motion presents, for the instant, the appearance represented in 

 the figure, in which, at spaces of from fourteen to fifteen cilia, there is a shaded inter- 

 section, which advances with a uniform movement from left to right as each cilium 

 successively assumes the position of that which follows it on the right-hand side. 



Suppose, now, the duration of each oscillation divided into fourteen instants, a 

 given cilium will occupy successively the positions A B, or A o, A n, A m, A I, A Jk, A i, 

 Ah, AC, in the space B A c, during the first half of the oscillation, the movement 

 taking place from left to right. The other positions during the second half of the 

 oscillation, the movement being from right to left, are, Aff, Af, Ae, A d, A c, A b, A a, 

 the position A a' being the same as A B, or A o, constituting the limit of the second 

 half of that oscillation and the commencement of a new one. 



In this manner the intersections, having the appearance of the teeth of a saw, will 

 appear to advance with a uniform motion in the direction of the movement of oscil- 

 lation, giving the appearance of a chain or row of pearls in motion in the case of a 



rectilinear row of cilia, or of a toothed wheel if the cilia are disposed in a circle. 



Vide Dujardin, Hist. nat. des Infusoires. 



