434 KOTIFERA. 



he bases the division of the class into orders. The peculiar movements 

 excited by the vibration of these organs was long a puzzle to the earlier 

 microscopic observers, who, imagining them to be really wheels turning 

 round with great velocity, were utterly unable to conceive what could 

 be the nature of the connexion between such appendages and the body 

 of the animal. The apparent rotation has, however, been long proved to 

 be an optical delusion, and to be produced by the progressive undulations 

 of the cilia placed in the neighbourhood of the mouth. 



(1123.) With respect to the agents employed in producing the ciliary 

 movement in the Rotifera, we are as much in ignorance as we are con- 

 cerning the cause of the same phenomenon in the Polygastrica. Ehren- 

 berg describes the cilia as arising from a series of lobes, as represented 

 in Notommata clavulata (fig. 230, a) ; these he regards as being mus- 

 cular, and capable of producing by their contractions the rapid vibra- 

 tions of the fibrillae attached to them. We confess, however, that such 

 lobes, even were their existence constant, seem very clumsy instruments 

 for effecting the purpose assigned to them ; and it is not easy to conceive 

 how the rapid and consecutive undulations, to which the appearance of 

 rotation is due, can be produced by organs of this description. 



(1124.) The observations of Dr. Arthur Farre* concerning the ciliary 

 movements appear best calculated to throw light upon the nature of the 

 action of these wonderful appendages, and to explain the cause of the 

 apparent rotatory motion of the so-called wheels of the Rotifera. The 

 very accurate observer alluded to remarks that, under high powers, the 

 cilia have the appearance of moving in waves, in the production of each 

 of which from a dozen to twenty cilia are concerned, the highest point 

 of each wave being formed by a cilium extended to its full length, and 

 the lowest point between every two waves by one folded down com- 

 pletely upon itself, the intervening space being completed by others in 

 every degree of extension, so as to present something of the outline of a 

 cone. As the persistence of each cilium in any one of these positions is 

 of the shortest possible duration, and each takes up in regular succession 

 the action of the adjoining one, that cilium which, by being completely 

 folded up, formed the lowest point between any two waves, in its turn 

 by its complete extension forms the highest point of a wave ; and thus, 

 while the cilia are alternately bending and unbending themselves, each 

 in regular succession after the other, the waves only travel onward, 

 whilst the cilia never change their position in this direction, having, in 

 fact, no lateral motion. 



(1125.) The whole of the ciliary movements are so evidently under 

 the control of the animal as to leave not the slightest doubt in the mind 

 of the observer upon this point. The whole fringe of cilia may be 

 instantly set in motion and as instantaneously stopped, or their action 

 regulated to every degree of rapidity. Sometimes one or two only of 

 * Phil. Trans, for 1837. 



