^213. 



THE CEPHALOPHORA. 



241 



CHAPTER V 



DIGESTIVE APPARATUS. 



§ 213. 



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 spec'al prehensile 

 organs. ''' These lips are quite contractile, and can evert and invert Ü\& 

 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 uf two horny, lamellifoim 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 

 consistsof 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 

 a sucker, of Pteropoda (CLio, Spongiobranchaea, 

 and Pneumodermon), ah'eady mentioned above 

 (§ 201). 



^ There is a retractile proboscis with Pneu- 

 modermon, Sjiongiobranchaea, Pterotrachea, 

 Thetis, B'lccinum, Doliam, Cijpraea, Murex, 

 Conus, Voluta, and many other Pectinibrau- 

 chia. 



3 The external borders of these jaws are easily 

 perceived between the lips, as with Scyllaea (Cu- 

 vier, Mem. loc. cit. fig. 6, a. 6, b.), with Tritonia 

 (^Savigny, Descript. de I'Egypte, Hist. Nat. II. 

 i?l. II. ÜK. 1-1'", and Delle Ciiiaje, Descriz. loc. 

 cit. Tav. XLII. fig. 1), and with Diphyllidia and 

 Bulla. They are found also directly behind the 

 lips with Veniiia, Aeolis, Amphorina, and Ter- 

 gipes {Alder, Hancock and Embleton, Ann. of 

 Nat. Hist. XIII. p. 162, PI. II. fig. 3, 4, XV. p. 4, 

 Pi. II. ; also (^uatre/ages, Ann. d. Sc. Nat. I. p. 



* [ § 213, note 4.] For many details upon the 

 oral organs of the Helicina, of an anatomical as 

 well as a zoological import, see Troschel (lieber 



21 



147, PI. V. fig. 5, and Nordmann, loc. cit. p. 12, 

 Tab. I. fig. 7). With /)en<a/i«»(, on the contrary, 

 the jaws are situated at the base of the oral cavity 

 (Desliai/es, loc. cit. p. 333, PI. XV. fig. 11, b. b. 

 15, 16, or in the Isis, 1832, p. 463, Taf. VI. fig. 15, 

 19, 20). 



4 This upper jaw is particularly developed with 

 the Limacina and Helicina ; see Cuvier, Mem. loc. 

 cit. Sur la Limace, &c., PI. II. fig. 4 {Limax) } 

 Troschel, in fViegmann^s Arch. 1836, I. p. 257, 

 Taf. IX. fig. 3-9 (Arion, Limax, Helix, Clau 

 silia, and Succinea), and Erdl, in Mar. fVag- 

 ner's Reisen in der Regentsch. Algier. III. p. 268, 

 Tab. XIII. XIV. With Lymnaens, and Planor- 

 bis, there are, beside, two small lateral jaws ; these 

 exist also with Valvata, and Palndina, where the 

 upper jaw is wanting. With Zephyrina, there are 

 also three jaws at the base of the pharynx ; see 

 Quatrefages, loc. cit. I. p. 132, PI. V. fig. 1.* 



die Mundtheile einiger Helicien, in jyiegTnann'» 

 Arch. 1849, p. 225). — Ed. 



