162 



OEGANS OF DIGESTION. 



matter, and forming a natural injection of the gastric cavi- 

 ties ; the anus opens at *, from which egesta are often seen 

 exuding. 



[ 314. The Eosphora najas is typical of the rotifera. The 

 body (fig. 1 72) is enclosed in a double 

 elastic tunic, into which the muscles are 

 inserted ; its anterior part is truncated, 

 and furnished with globular bodies armed 

 with vibratile cilia; this rotatory apparatus 

 is moved by muscles inserted into the 

 base of the ciliiferous organs ; the eyes are 

 seen at a, , b ; the pharynx (c) is large 

 and capacious, and the stomach (d} is 

 provided with a triturating apparatus, 

 which in many allied genera is armed with 

 jaws. The intestine terminates in the anus 

 at d; the ovary, with many ova, is seen at/. 

 The posterior extremity of the body is fur- 

 nished with a pair of forceps, by which 

 the rotiferse attach themselves at pleasure. 

 [315. The digestive organs in the ACA- 

 LEPH^; present many phases of develop- 

 Fig. 172. Eosphora ment ; in some, their pendant arms are 

 na J as - traversed by tubes, through which aliments 



pass to reach the gastric cavity. The most remarkable structure 

 of this class exists in the Rhizostoma Cuvieri, of which a longi- 

 tudinal section is seen in fig. 1 73 ; the gastric cavity (b), sur- 

 rounded by four respiratory chambers, occupies the upper part 

 of the disc ; the peduncle, hanging from the centre of the disc, 

 divides into eight arms, four of which are seen terminating in 

 spongy expansions, and perforated with numerous apertures, 

 leading into a common channel (c) ; these vessels traverse the 

 centre of the tentacula; in the middle and upper part of 

 each of the arms are numerous fimbriated folds, in which ves- 

 sels ramify that likewise open into the central canals ; these, 

 uniting two and two, enter the gastric cavity by four principal 

 trunks. The walls of the stomach are divided by delicate 

 septse from the four ovarial sacs (d), which open externally by 

 distinct apertures (a, a) ; from the periphery of the stomach 

 sixteen vessels radiate, which divide and anastomose as they 

 proceed towards the margin of the disc, where they form a net- 



