^^ 152j 153. THE ANNELIDES. 163 



CHAPTEH V. 



DIGESTIVE APPARATUS. 



§ 152. 



The digestive canal of the Annelides, which is organized after very dif- 

 ferent types, opens always at the anterior part of the body by a mouth, and 

 at the posterior part by an anus. It is situated upon the axis of the body, 

 and is usually straight, rarely having convolutions. Often it is divided 

 into many sections, to which the names of pharynx, oesophagus, stomach, and 

 intestine, may be given. The mouth is usually surrounded with thick lips, 

 and, with many Capitibranchiati, it has very erectile tentacles and cirri, 

 which may be not only tactile but prehensile organs, ^^^ With others of 

 this group, the food is taken in by the action in the water of the ciliated 

 branchial rays which surround the mouth in an infundibuliform or spiral man- 

 Der.'-> But usually the food, both soft and solid, is seized by the protube- 

 rant lips, and swallowed by the very muscular pharynx. Many Annelides can 

 also suck in liquid food through their organs of deglutition. ^•■'> The stomach 

 and intestine is lined with ciliated epithelium. The intestinal canal, whose 

 walls are in general very thin, is either closely embraced by the parenchy- 

 ma of the body,'*' or, when there is a cavity of the body, is supported and 

 constricted by numerous muscular septa.'''* 



/. Organs of 'Deglutition and Mastication. 



§ 153. 



The mouth of the Nemertini is situated upon the ventral surface, and 

 usually at some distance from the cephalic extremity. It is a longitudinal 

 «rifice opening into a long, muscular and very spacious pharyngeal tube.<^' 

 This tube is intimately united with the parenchyma of the body, and after 

 passing a short distance backward, joins directly with the intestinal canal. <-> 

 AVith many Hirudinei, the mouth is at the anterior extremity. Its ante- 

 rior border projects so as to form a kind of lip, which the animal can vol- 

 untarily change into a sucker. Other species have a complete oral sucker, 



1 Terebella, Amphi .rite, and Siphonostomum. Thus Dus;6s, with Polystemma (Prostoma) arma- 



2 Sabella, and Serpula. tinn (Ann. d. Sc. Nat. XXI. 1830, p. 74, PI. II. 



3 Many Hii;udinei. fii;. 5), and Quatrefag'es, with Nemertes man- 



4 This is true of the Hirudinei, and many Nemer- dilla (Icon, du Rögne anim. de Cuvier, Zooph. PI. 

 tini. XXXIV. fig. 2), regard the long canal wliich opens 



5 With the Chaetopodes. at the cephalic extremity, as the pharyngeal tube, 

 1 See Delle Chiaje, Memorie loc. cit. Tav. and the spines at its base as masticatory organs ; 



JjXXVIll. &g.S.h.(Potiaireniculata) ; Husch/ie, while OrsZed (Beschreib, d. Plattwürmer, p. 22, 



Isis, 1830, Taf. VII. fig. 2 {Notofspermus drepa- Tat'. III. fig. 41, 49, 50) regards this wliole appa- 



«ensz«),- Gr«*e, Aktinien, Echinud. und W^iirmer, ratus with Tetrastemma as a copulatory organ 



&c., loc. cit. fig. 7, a. {Meckelia annulata) ; Rath- (see below). In my opinion, the animals here cited 



A-<?, Danzig. Schrift, loc. cit. Taf. VI. fig. 8. b. {ßor- do not belong even to the Nemertini. 



lasia fttriata); and Ehrenbers, Symbol. Physic. ü Borlasia (Rtithke, loc. cit. p. 96, Taf. VI. fig. 



Phytozoa Turbellaria, Tab. IV. fig. 4. g. {Micrura 10, 11) and Polia {Delle Chiaje, loc. cit. II. p. 



Jasciolata). Ehreuberg, moreover, was deceived 407, Tav. XXVIII. fig. 3, j., or Isis 1832, p. 648, 



in regarding this mouth as the opening of the gen- Taf. X. fig. II. 3, j.). With Meckelia annulata, I 



ital organs, and in taking the proboscideal organ of have found the pharyngeal tube arranged in tha 



this species, for the true mouth. There is yet in same way. 

 this respect much contradiction among naturalists. 



