>§.§ 152, 153. THE ANNELIDES. 163 



CHAPTER 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 phar3Mix, 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- 

 ner. ^-^ But usually the food, both soft and solid, is seized by the protube- 

 rant lips, and swallowed by the ver}' muscular pharynx. Many Annelides can 

 also suck in liipiid 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 Deglutitio7i 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 

 orifice 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. <^ 

 With 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, Amphitrite, and Siphonostomxtm. Thus Dus;is, with Polystemma (Prostoma) arma- 



a Sal/elld, iinsi Serpu/a. tinn (Anil. d. Sc. Nat. XXI. 1S30, p. 74, PI. II. 



3 Many Hirudinei. fi;r. 5), and Quatrefa^ea, with Nemertes man- 



4 This is true of the Hirudinei, and many Nemer- dilla (Ic:)n. du K^gne anim. de Cuvier, Zooph. PI. 

 tini. XXXIV. tig. 2), regard the long canal which opens 



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

 1 See Delle Chiaje, Memoria be. cit. Tav. and the spines at its base as masticatory urg;uis } 



JjXXXlll. fi'^.S.b.(Polia S'enicu/ata) ; HiiacUe, while Or.s^ed (Beschreib. d. Plattwuimer, p. 22, 



Isis, 1830, T.if. VII. fig. 2 {Noto'ipermu^ drepa- Taf. III. fig. 41, 49, 50) regards this whole appa- 



nenxU) ; Grube, Aktinien, Echinod. u:id Wurmer, ratus with Tetraslemma as a copulatory organ 



&c., loc. cit. fig. 7, a. (^Mecketia annulata) ; Rath- (see below). lu my opinion, the animals herecited 



i-^, Danzig. Schrift. loc. cit. Taf. VI. fig. 8. 1). {Hot- do not belong even Ui th j Nemertini. 

 tafia striata); and Ehrenbersr, Symbol. Physic. 'i Borlasia {Rnthki, loc. cit. p. 96, Taf. VI. flg. 



Phytozoa Turl^ellaria, Tab. IV. fig. 4. g. {Micriira 10, 11) and Polia {Delle Chiaje, loc. cit. II. p. 



fasciolata). Ehrenbers, moreover, was deceived 407, Tav. XXVIII. fig. 3, j., or Isis, 1S32, p. (US, 



in regarding tliis mouth as the opening of the gen- Taf. X. fig. II. 3, j ). With Aleckelia annulata, i 



ital organs, and in taking the proboscideal organ of have found the pharyngeal tube arran„"j 1 \n the 



this si>ecies, fn- th.; truii mouth. There is yet in same way. 

 this respect much cjntraJiction among naturalists. 



