Characteristics of Rotifers. 289 



them as " animals with club-shaped bodies, able to contract 

 themselves into a ball, and capable, when extended, of 

 drawing in their anterior extremity, or protruding in its 

 place a double lobe with cilia, presenting the aspect of 

 two wheels in motion; terminating posteriorly by a many- 

 jointed tail, the last joint carrying a pair of fleshy fin- 

 gers or styles. Swimming by means of vibratile cilia, or 

 crawling like leeches by alternately fixing the two extremities 

 of the elongated body. Jaws stirrup-like. Two or more red eye 

 points." We shall presently see the real nature of the jaws so 

 described ; but with the mention of the aspect of this family 

 we conclude our brief review of some of the leading varieties 

 of rotifer forms. 



Let us now revert to the trochal disks and adjacent ciliary 

 apparatus. 



In the first place it may be generally remarked that the 

 ciliary organs of rotifers are more complicated than they may 

 appear at first sight, or than they are sometimes described. An 

 immense difficulty in the way of understanding their real struc- 

 ture and action arises from the awkward perspective in which 

 we usually see them. It is but rarely that we can look straight 

 down upon them so as to see their ground plan at one glance. 

 Ordinarily, we see an imperfect sectional view, as if we saw a 

 perpendicular slice of a house exhibiting in section the front 

 set of rooms, and with imperfect glimpses of other rooms 

 behind. We have also to do with objects so minute, and with 

 parts so transparent, that only the most careful focussing and 

 illumination, conjoined with much thought, can enable us even 

 approximately to ascertain the exact superposition of different 

 structures and the way in which they co-operate with each 

 other. Mr. Huxley's paper on Lacinularia socialis, in the 

 " Transactions of the Microscopical Society " for Dec. 1851, 

 will give us valuable help in this matter. The trochal, or 

 wheel-disk of the Lacinularia is, according to his description, 

 (C wide, and horse-shoe shaped. . . . The edge of the disk 

 has a considerable thickness, and presents two always distinct 

 margins, an upper and a lower, of which the former is thicker 

 and extends beyond the latter. The large cilia are entirely 

 confined to the upper margin and seated upon it ; they form a 

 continuous horse-shoe shaped band, which, upon the oral side, 

 passes entirely above the mouth. The lower margin is smaller, 

 and less defined than the upper, its cilia are fine and small, not 

 more than one-fourth the size of those of the upper margin. 

 On the oral side this lower band of cilia forms a V-shaped 

 loop. About the middle of this margin, on each side, there is 

 a small prominence, from which a lateral ciliated arch runs 

 upwards into the buccal cavity, and below becomes lost in the 

 VOL. XII. — NO. iv. u 



