. Elements of Comparative Anatomy. 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
. Elements of Comparative Anatomy. 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 § 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
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