ALIIMENTAEY CANAL OF VEET^IES. 



161 



The hind-gut follows a constriction of tlie somewhat more deeply- 

 placed pyloric portion^ and, ascending by the side of the fore-gut, is 

 continued into an anus {B a), which is placed close to the mouth, but 

 always below and outside the circlet of tentacles. The hind-gut is 

 sometimes widened (Flustra). 



The ciliated tentacles function as accessory organs of nutrition, 

 food being brought to the fixed animals with the changing water. 



In the Pedicelhnas the same parts can be made out as in the 

 true Bryozoa, but the stomach has no 

 cfficum. 



The enteric canal of the Rotatoria 

 exhibits sometimes agreement with lower 

 conditions, for it may consist of fore- 

 and mid-gut only, the hind-gut being 

 absent (species of Notommata), while on 

 the other hand it is more highly de- 

 veloped, owing to the differentiation of 

 masticatory organs in the most anterior 

 portion. These are formed by chitinous 

 structures, placed at the sides and oppo- 

 site to one another ; they are provided 

 with tooth-like processes, etc. (Fig. 4o, 

 in). The fore-gut commences with the 

 mouth, which lies below the ciliated 

 velum, and is distinguished by its lesser 

 width from the mid-gut (ordinarily called 

 the " stomach "). Where a hind-gut is 

 continued on fi'om the mid-gut, it turns 

 to the dorsal surface of the body, to 

 open into a cavity common to the open- 

 ings of the excretory and sexual systems 

 — the cloaca — a peculiarity not found in 

 other divisions of Vermes. 



§ 131. 



Fig. 72. Enteric caual of 

 Bonellia. The proboscis of 

 the animal is coiled, so that the 

 whole of it cannot be seen. 

 p Front of the iJroboscis. 

 ss ' Groove of the proboscis, ii 

 Enteric canal, in Mesenteric 

 filameuts : they are only drawn 

 in the anterior region, g Ex- 

 cretory organs, c Cloaca, m Ute- 

 rus (after Lacaze-Duthiers). 



In the Gephyrea the three divisions 

 of the enteric canal are, as a rule, distinct 

 in the earlier stages only ; in some, how- 

 ever, for a longer time (Priapulus) ; while in others, as the enteric 

 tube elongates, the separation becomes less noticeable. The enteron 

 then forms a tube, which is generally a good deal longer than the 

 body, and which does not vary much in diameter. It is either dis- 

 posed in several partially- coiled longitudinal loops, when the anus 

 is on the dorsal surface of the animal (Sipunculus, Phascolosoma) ; 

 or the enteron (Fig. 72, i) passes to the posterior end of the body, 

 in numerous shorter coils, without forming large longitudinal loops, 

 and ends in the anus, which is placed there (Echiurus, Bonellia). 

 The latter agree with the majority of the other Vermes in the aboral 



