^>§. 207, 208. THE CEPHALOPHORA. 233 



§207. 



The nervous system of tVie Cephalophora is enveloped by a very distinct 

 fibrous neurolemma containing otten various pigments, which, in some 

 species, give it, and especially the ganglia, a well-marked color/*' The 

 neurolemma enters the ganglia and forms there numerous septa which 

 separate the ganglionic globules into groups. These are very distinct, 

 and although of variable size, always contain a very large nucleus 

 composed of obscure granules in the midst of which are seen usually two 

 to four transparent nucleoli of unequal size.^-* 



These ganglionic globules are very often pedunculated, '''> and then their 

 very slender peduncles or processes usually extend far into the nerves 

 -which are given ofi' from the ganglion, thus leading one to infer that these 

 globules are the origin or termination of the nervous fibres.*^* Moreover, 

 these primitive fibres which traverse the ganglia, are always situated in 

 that portion of them which is contiguous to the oesophagus or pharynx, 

 while the opposite portion is occupied by the ganglionic globules. 



§ 208. 



There is a great variety in the form and arrangement of the different 

 j)arts of the nervous centre, according to the orders and families, as fol- 

 lows.^*' 



1. The Heteropoda quite resemble the Lamellibranehia by their 

 •widely-separated ganglia connected by very long commissures. At the 

 anterior extremity of their body, and above the oesophagus, there is a 

 •cerebral mass which sends backwards two long nervous cords, which, after 

 passing along each side of the intestinal canal, terminate by entering the 

 inferior ganglionic portion [Ganglion pedale), situated near the ventral 

 surface. The cerebral portion furnishes nerves to the organs of sense, to 

 the skin, and to the lips, while the posterior jjortion sends them chiefly to 

 the foot, and to the muscles of the tail.'-' 



1 These ganglia are orange-colored with Lym- < See HelmhoUz, De fabr. Syst. nerv, evert, loc. 

 naeu.i, and red with Planorbis, Paludina, Hya- cit. p. 10 ; Hannover, loc. cit. and Will, in Mill' 

 lea, Pleurobranchus. ler's Arch. 1844, p. 76.* 



2 Hannover (Recherch. microscop. sur le Sys- 1 For the descriptions and figures of the nervous 

 teme nerveu.K, 184-1, p. 69, PI. VIII.) has very well system of several Cephalophora, see Cuvier, Mem. 

 ■described and figured the ganglion-globules of loc. cit. ; Garner, Trans, of tlie Linn. Soc. XVII. 

 Helix and Liniax. p. 488 ; Ryvier Jones, Cyclop, of Anat. p. 392, 



3 Judging from Ehrenberg^s figure (Uner- Art. Gasteropoda; Anderson, Ibid. III. p. 605, 

 kannt. Struljtur &c. Tab. VI. fig. I. 1-.) of the Art. Nervous System ; and Fan Beneden, Exer- 

 pedunculated ganglion-globules of Avion empiri- cises zoot. loc. cit.f 



coram, lie was not aware of the large nuclei which ^ See Milne Edwards, Ann. d. Sc. Nat. XVIII. 

 they contained. 1842, p. 326, PI. XI., and Delle Chiaje, Descriz. II. 



* [§ 207, note 4.] Leidy^s results, after very para, &c., loc. cit. p. 152, Taf. XIII. fig. 49, a. ß. 



■careful dissection, do not accord with these, for he {Paludina); Blanchard, Ann. d. Sc. Nat. XI. 



observed none of the nerve-fibres originate or ter- 1849, p. 78, PI. III. fig. 1, PI. IV. fig. 1 (Janus) ; 



tninate in the ganglionary globules; see loc. cit. Middendorff, loc. cit. p. 75, Taf. IX. (Chiton); 



vol. I. p. 243. — Ed. Leidy, loc. cit. PI. I. fig. I. 11-14 (Limax), PI. 



t [ § 208, note ].] See also Alder and Hancock, IV. fig. V. 15-17 (Faginulus), PI. V. fig. I. 32, 33, 



loc. cit. Part. II. PI. II. fig. 9 (Dendronotus), PI. 34 (Bulimus), PI. VI. fig. II. 25, PI. VII. fig. 



IV. fig. 16 (Doto) ; Part. III. PI. VIII. fig. 8 VIII. 20, PI. IX. fig. IV. 26, -It, PI. X. fig. IV. 



iEolis); Part. IV. PI. V. fig. 1, k. (Scyllaea) ; 24, 25, 26 (Helix); PI. XIII. fig. IV. (Helicina), 



Part V. PI. II. fig. 13 (Doris), PI. XLIII. fig. 10 PI. XIV. fig. IV. PI. XVI. (Glandina). — 'E.v. 

 {Antiopa) ; then Leydig, Ueber Paludina vivi- 



2i)* 



