434 MICROSCOPIC FORMS OF ANIMAL LIFE. 



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 habitu- 

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

 crawl over hard surfaces. As these have already been fully de- 

 scribed, it is not requisite to dwell longer upon them. 



III. The next group consists of those Eotifers which seldom or 

 never attach themselves by the foot, 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 Brachionians 

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

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

 (Figs. 200, 203) ; which is, moreover, enclosed in a sort of cuirass, 



Fia. 203. 



Noteus quadricornis ; A, dorsal view; B, side view. 



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 some- 

 times 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, which is one of the 

 largest of the Rotifera, and which was employed by Prof. Ehren- 

 berg as the chief subject of his examination of the internal struc- 

 ture of this group ; as does also the Notommata, the curious con- 

 dition of whose male has been already referred to ( 279). 



