ALIMENTARY CANAL 



271 



family; but developmentally they result from modifications of 

 two rows of small, similar pieces. 1 



The intestine is generally straight and cylindrical, and is usually 

 constricted by the septa, if these are present. In the Polynoids 

 the intervening sacculations become so long as to receive the 

 name of " caeca," which, in Aphrodite, become enormously elon- 

 gated (Fig. 142) ; there are eighteen pairs of them (c),each being 



3,4- 



Fia. 141. A, Alimentary canal of Syllid : B, trans- 

 verse section of pharynx of the same ; b, buccal 

 region ; d, oesophageal outgrowth ; g, salivary 

 glands ; i, intestine ; j, tooth ; p, pharynx ; 3, gizzard : 

 C, alimentary canal of Petta (after Wiren) ; t, in- 

 testine ; o, oesophagus ; r, rectum ; , stomach. 



FIG. 142. Alimentary canal 

 of Aphrodite, x 1. (From 

 Gegenbaur.) a, Anus ; b, 

 pharynx ; c, caeca ; o, 

 mouth. 



a slender tube bent upon itself, giving off short branches and 

 dilated distally, where it lies in the base of the parapodium. 



The intestine is looped in a few genera only, as in Trophonia, 

 or coiled, as in Sternaspis, Petta (Amphictenid, Fig. 141, C), and 

 Ammotrypane. In the course of the tube there may be a thick- 

 walled muscular gizzard, with hard chitinous lining, as in certain 

 Terebellids, where it appears to replace, in function, the pharynx 

 of the Nereidiformia ; in the Syllidae the gizzard is present in 

 addition to the pharynx (Fig. 141, A). 



Glandular appendages of the oesophagus are present in many 



1 Korechelt, "Uber Ophryotrocha puerilis," Zeitsckr.f. *><;. Zool. Iv. 1893, p. 224. 



