rotifera: — melicerta; hydatixa. 479 



protected by a most curious cylindrical tube, composed of little 

 rounded pellets agglutinated together; this is obviously an artificial 

 construction, and Mr. Gosse has been fortunate enough to have 

 an opportunity of watching the animal whilst engaged in building 

 it up. Beneath a projection on its head, which he terms the chin, 

 there is observed a small disk-like organ, in which, when the 

 wheels are at work, a movement is seen very much resembling 

 that of a revolving ventilator. Towards the disk the greater 

 proportion of the solid particles that may be drawn from the 

 surrounding liquid into the vortex of the wheel-organs, are driven 

 by their ciliary movement, a small part only being taken into the 

 alimentary canal ; and there they accumulate until the aggrega- 

 tion (probably cemented by a glutinous secretion furnished by 

 the organ itself) acquires the size and form of one of the globular 

 pellets of the case ; the time ordinarily required being about 

 three minutes. The head of the animal then bends itself down, 

 the pellet-disk is applied to the edge of the tube, the newly- 

 formed pellet is left attached there, and, the head being lifted 

 into its former position, the formation of a new pellet at once 

 commences. 



ii. The next of M. Dujardin's primary groups (ranged by him, 

 however, as the third) consists of the ordinary Rotifer and its 

 allies, which pass their lives in a state of alternation between the 

 conditions of those attached by a pedicle, of those which habitually 

 swim freely through the water, and of those which creep or crawl 

 over hard surfaces. — As these have already been fully described, 

 it is not requisite to dwell longer upon them. 



in. The next group consists of those Rotifers which seldom or 

 never attach themselves by the loot, but habitually swim freely 

 through the water ; and putting aside the peculiar aberrant form 

 Albertia, which has only been found as a parasite in the intestines 

 of Worms, it may be divided into two families, the Brachioniaas 

 and the Furcularians. The former are for the most part dis- 

 tinguished by the short, broad, and flattened form of the body 

 (Figs. 243, 247); which is, moreover, enclosed in a sort of cuirass, 

 formed by the consolidation of the external integument. This 

 cuirass is often very beautifully marked on its surface, and may be 

 prolonged into extensions of various forms, which are sometimes 

 of very considerable length. The latter (corresponding almost 

 exactly with the Hydatinece of Prof. Ehrenberg) derive their name 

 from the bifurcation of the foot into a sort of two-bladed forceps ; 

 their bodies are ovoidal or cylindrical, and are enclosed in a flexible 

 integument, which is often seen to wrinkle itself into longitudinal 

 and transverse folds at equidistant lines. To this family belongs 

 the Hydatina senta, one of the largest of the Rotifera, which was 

 employed by Prof. Ehrenberg as the chief subject of his examina- 

 tion of the internal structure of this group ; as does also the 

 Asplanchna, the curious condition of whose male has been already 

 referred-to (§ 360). 



