428 MICROSCOPIC FORMS OF ANIMAL LIFE. 



278. Ill considering the internal structure of Rotifera, we shall 

 take as its type the arrangement which it presents in the Rotifer 

 vulgaris (Fig. 101) ; and specify the principal variations exhibited 

 by others. The body of this animal, when fully extended, 

 possesses greater length in proportion to its diameter than that 

 of most others of the class ; and the tail is composed of three 

 joints or segments, which are capable of being drawn up, one 

 within another, like the sliding-tubes of a telescope, each having 

 a pair of prongs or points at its extremity. Within the external 

 integument of the body, are seen a set of longitudinal muscular 

 bands (A), which serve to draw the two extremities towards each 

 other ; and these are crossed by a set of transverse annular bands, 

 which also are probably muscular, and serve to diminish the 

 diameter of the body, and thus to increase its length. Between 

 the wheels is a prominence, bearing two red spots (>), supposed 

 to be rudimentary eyes, and having the mouth (a) at its extre- 

 mity ; this prominence may be considered, therefore, as a true 

 head, notwithstanding that it is not clearly distinguishable from 

 the body. This head also bears upon its under surface a projecting 

 tubular organ (d), which was thought by Professor Ehrenberg to 

 be a siphon for the admission of water to the cavity of the body 

 for the purpose of respiration ; this, however, is certainly not 

 the case, the tube being imperforate at its extremity; and there 

 seems much more probability in the idea of Dujardin, that it re- 

 presents the antennce or palpi of higher Artie ulata, the single 

 organ being replaced in many Rotifera by a pair, of which each 

 is furnished at its extremity with a brush-like tuft of hairs that 

 can be retraced into the tube. The oesophagus, which is narrow 

 in the Rotifer, but which is dilated into a crop in Stephanoceros 

 (Fig. 202) and in some other genera, leads to the masticating 

 apparatus, which in these animals is placed far behind the mouth, 

 and in close proximity to the stomach. It consists of a pair of 

 stirrup-shaped jaws (Fig. 201, e) each having from one to five teeth 

 (in Rotifer, two), which appear to contain mineral matter and to 

 be of harder texture than the rest of the fabric ; these jaws are 

 put in action by powerful muscles, and are so moved that all the 

 food which passes into the stomach is subject to be divided and 

 torn by their teeth. In many Rotifera, the conformation of this 

 masticating apparatus is extremely complicated. The form of 

 the alimentary canal varies; this being sometimes a simple tube, 

 passing without enlargement or constriction from the masticat- 

 ing apparatus to the anal orifice at the posterior part of the body ; 

 whilst in other instances there is a marked distinction between 

 the stomach and intestinal tube, the former being a large globu- 

 lar dilatation immediately below the jaws, whilst the latter is 

 cylindrical and comparatively small. The alimentary canal of 

 Rotifer most resembles the first of these types, but presents a 

 dilatation (Z) close to the anal orifice, which may be considered 

 as a cloaca; that of Brachionus (Fig. 200) is rather formed upon 



