236 



THE CEPHALOrUORA. 



§210. 



The posterior plexus is composed of a single mass, rarely of two separate 

 ganglia. It is situated under the digestive canal or between its coils, and 

 from it pass off nerves to the intestine, the liver, and the genital glands, 

 beside two cords of communication with the lower portion of the oesophageal 

 ring.''' 



CHAPTER IV, 



ORGANS OF SENSE. 



§210. 



The Tactile organs of the Cephalophora consist of two to four contractile 

 tentacles situated upon the heud, or the anterior part of the back.''* They 

 receive nerves of considerable size from the cerebral mass, which have some- 

 times a ganglionic enlargement in the extremity of the tentacle.'-' With 

 some Gasteropoda these tentacles are hollow and button-like at their ex- 

 tremity, and can be inverted like the finger of a glove. '^' But with the 



sia, p. 23, PI. IV. fig. 1, c. ; sur la Lymnee, p. 

 9, PI. I. fig. 11, u. ; sur rOncliidie, p. 14, PI. I. 

 fig. 6, o. Brandt (.Mt-d. Zool. II. p. 328, Tab. 

 XXXIV. fig. 11, 13) has described it with Helix 

 pomatia ; Fan Beneden (loc. cit.), with Amphi- 

 pep/ea, and Treviranus (Beobacht. au.s. d. Zoot. 

 und Pliysiul. p. 42, Taf. IX. fig. 60), with Umax. 

 See also the researches of Schlemm (Dissert, de lie- 

 pate ac bile crustaceorum et molluscorum quorun- 

 dara, Berol. 1844, p. 22, Tab. I. fig. 2, 3), upon the 

 hepatic nerves of Gasteropoda. Delle C/iiaje aho, 

 h;is seen tliis plexus with Doridinm. and Pleuro- 

 branckm (Memor. II. p. 123, Tav. X. fig. 7, p. 

 and III. p. 153, Tav. XLI. fig. 8, p.). According 

 til Garner (loc. cit.), there is a double Ganglion 

 pharynseum inferius with, also, Scyllaea, Doris, 

 and Ei)lis. With Patella, on the contrary, he 

 found this anterior Plexus splanchnicus couipused 

 of three ganglia, two upon the sides, and the third 

 median and a little behind. 



According to Fan Beneden (Exercices zoot. 

 Faso. I. p. 30, PI. I. fig. 12, c), there is a similar 

 disposition with Amphipeplea. AVith the Iletero- 

 p'lila, this plexus is highly developed, composed of 

 two ganglia, from which pass off long cords of com- 

 munication to the cerebral mass ; see Milne Ed- 

 wards, Ann. d. Sc. Nat. XVIII. p. 327, PI. XI. 

 fig. 1, s. X. and fig. 2, e. f. ; and Delle Chiaje, 

 Descriz. &c. loc. cit. Tav. LXIII. fig 14, 1. and 

 LXIV. fig. 11, d. {Carinaria and Pterotrachea). 

 The Pteropoda also have this plexus ; but its two 

 ganglia are more or less intimately fused, and as 

 the cerebral mass is here replaced by a simple col- 

 lar, it does not connect with it, but with the infe- 

 rior portion of tlie oBsojihageal ring ; see Van Be- 

 neden, Exercices zoot. Fasc. II. p. 11, et seq. I'l. I. 

 fig. 9, 10, li. fig. 8, 10, III. fig. 6, 9, and V. fig. 



* [ § 209, note 2.] For the splanchnic nervous 

 system of the terrestrial Gaslero|)iKla, see Leidy, 

 loc. cit. PI. XIII. fig. IV. 2 {Utlicinä), PI XIV. 

 fig. IV. 3 {Glandina), and PI. XVI. fig. II. 2 

 (//erta-). 



See also for that of the Nudibranchia, Alder 



13 (Cymbulia, Tiedemannia, Hyalea and Lima- 

 cina.)* 



3 The Plexus splanchnicus posterior with its 

 two long cords of communication is ([uite apparent 

 with Aplysia (see Cuiner, loc. cit. p. 23, PI. IV. 

 fig. 1, R.). Delle Chiaje (Memor. Tav. V. fig. 1, 

 m, X. fig. 7, o. and XLI. fig. 8, y. y.), has observed 

 it with Doridium, and Pleurobranchus, be- 

 side the genus just mentioned , and in Pleura- 

 branchtis, he found it composed of two entirely 

 separated ganglia. Fan Beneden (Exerc. zoot. 

 Fasc. I. p. 46, PI. I. fig. 3-5) has found it com- 

 posed of only a single ganglion with Pneumoder- 

 mon. Milne Edwards (loc. cit. p. 329, PI. XI. 

 fig. 1, u. V. 6), has observed in the visceral sac of 

 Carinaria, first, a double Ganglion abdominale, 

 which receives two long cords of communicatiou 

 from the cerebral mass and from the Ganglion 

 pedale, and then a Ganglion anale, communi- 

 cating with the two abdominal ganglia. 



1 There are most usually two tentacles. But with 

 Limax, Arion, Helix, Achatina, Clausilia, and 

 other Helicina, there are four. They are wholly 

 wanting with Sagitta, Cleodora, Cuvieria, Hya- 

 lea, Pterotrachea, Lissosoma, Rhodope, Phyl- 

 lidia, and Dentaliuin. 



'■i This swelling exists not only with the inferi- 

 or and eyeless tentacles, but also the superior ones 

 bearing eyes, with several Liniacina and Helicina. 

 However, no ganglionic glolmles are seen in it, and 

 only a finely-granular substance Ues interposed be- 

 tween the primitive fibres. 



3 With the Liniacina and Helicina, these organs 

 are invested by a muscle which arises upon the 

 columnella or upon the internal surface of the 

 mantle, and is inserted at the extremity of each 

 tentacle. 



and Hancock, loc. cit. (Eolis, Doris, Antio- 

 pa, &c.). 



According to Middendorff (loc. cit. p. 76), Chi- 

 ton has a complex sjilaiichnic nervous system 

 which is widely distributed over the digestive or- 

 gans and their auxiliary glands. — Ed. 



