^ 213. THE CEPHALOPHORA. 241 



CHAPTER V 



DIGESTIVE APPARATUS. 



§ 21.3. 



Tlie highly-developed digestive organs of the Cephalophora always com- 

 mence at the anterior extremity of the body, with a round, oral orifice, 

 which is surrounded with tumid lips, but rarely has special prehensile 

 organs.*^' These lips are quite contractile, and can evert and invert the 

 mouth ; with many species, they can be prolonged into a cylindrical pro- 

 boscis.® The walls of the oral cavity are very muscular, and, with the 

 majority of the species, form a round and often very large pharynx. The 

 epithelium of this cavity is frequently developed into collars or callosities 

 which serve as masticatory organs. With some Gasteropoda, this apparatus 

 is composed of two horny, lamelliform jaws, which have a truncate, convex, 

 internal border, and move upon each other in a lateral manner.*''* These 

 jaws are situated, sometimes directly behind the oral orifice, and sometimes 

 at the base of the pharynx. 



Many other Gasteropoda have only an upper jaw enchased in the roof 

 of the oral cavity, and which is easily seen from its deep-brown color. It 

 consists of a transverse, semilunar, horny plate, upon whose anterior surface 

 are several vertical crests, which terminate upon the free border by as 

 many tooth-like processes.*'" 



Nearly all the Cephalophora have a longer or shorter fleshy mass, ad- 

 hering to the base of the pharynx, and which is sometimes grooved longi- 

 tudinally ; it is quite comparable to a Tongue. Sometimes it is very large 

 and contained in a membranous sheath at the base of the pharynx. It is 

 always armed with horny, denticulated spines and plates, which are very deli- 

 cate, and arranged in quite elegant, longitudinal and transverse rows. The 



1 Such are the tentacular appendages which have 147, PI. V. fig. 5, and Nordmann, loo. cit. p. 12, 

 a sucker, of Pteropoda (Clio, Spon^iobranchaea, Tab. I. fig. 7). With £)enZn/i«»i, on the contrary, 

 and Pneumodermon), already mentioned above the jaws are situated at the base of tlie oral cavity 

 (^ 204). {Deshayes, loc. cit. p. 333, PI. XV. fig. 11, b. b. 



2 There is a retractile proboscis with Pneu- 15, 16, or in the Isis, 1832, p. 463, Taf. VI. fig. 15, 

 modermon, Span giobranchaea, Pterotrachea, 19, 20). 



Thetis, Buccinum, Dolium, Cypraea, Murex, 4 Tliis upper jaw is particularly developed with 



Conus, Valuta, and many other Pectinibran- the Limacina and Helicina ; see Cj/Di'er, 5lem. loc. 



chia. cit. Sur la Limace, &c., PI. II. fig. 4 (^Lirnax) ; 



3 The external borders of these jaws are easily Trosckel, in fViegmanii's Arch. 1836, I. p. 267, 

 perceived between the lips, as with Scyllaea (Cu- Taf. IX. fig. 3-9 (Arion, Limax, Helix, Clau- 

 vier, Mem. loc. cit. fig. 6, a. 6, b.), with Tritonia silia, and Succinea), and Erdl, in Mor. JVag- 

 (Savigny, Descript. de I'Egypte, Hist. Nat. II. ner^s Reisen inder Regentsch. Algier. III. p. 263, 

 PI. II. fig. l^-l'o, and Delle Ckiajc, Descriz. loc. Tab. ,XIII. XIV. With Lymnaeu.t, and Planor- 

 cit. Tav. XLII. fig. 1), and with Diphyllidia and bis, there are, beside, two small lateral jaws ; these 

 Bulla. They are found also directly behind the exist also with Valvata, and Paludina, where the 

 \\ys, -with Venilia, Aeolis, Amphorina, and Ter- upper jaw is wanting. With Ze;)Ai/r!na, there are 

 gipes (Alder, Hancock and Embleton, Ann. of also three jaws at the base of the pharynx ; see 

 Nat. Hist. XIII. p. 162, PI. II. fig. 3, 4, XV. p. 4, (^uatre/ages, loc. cit. I. p. 132, PI. V. fig. 1.* 



PI. II. ; also ^uatrefages, Ann. d. So. Nat. I. p. 



* [ § 213, note 4.] For many details upon the die Mundtheile einiger Helicien, in IViegmann's 

 oral organs of the Ilelicina, of an anatomical as Arch. 1849, p. 225). — Ed. 

 well as a zoological import, see Troschel (Ueber 



