^^ 207, 208. 



THE CEPHALOPHORA. 



233 



§ 207. 



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

 fibrous neurolemma containing often 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 off 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 j^harynx, 

 while the opposite portion is occupied by the ganglionic globules. 



§ 208. 



There is a great variety in the form and arrangement of the difi'erent 

 parts of the nervous centre, according to the orders and families, as fol- 

 lows.*^' 



1. The Heteropoda quite resemble the Lamellibranchia 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 [Gaiiglioii 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 portion sends them chiefly to 

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



1 These ganglia are orange-colored with L,ym- 

 ■naeus^ and red with Planorbis, Paludina, Hya- 

 lea, PleuTobranchus. 



- Hannover (Recherch. mlcroscop. sur le Sys- 

 time nerveux, lS-14, p. 69, PI. VIII.) has very well 

 described and figured the ganglion-globules of 

 Helix and Limax. 



3 Judging from Ehrenberg''s figure (Uner- 

 liannt. Struktur &c. Tab. \l. fig. I. 1-.) of the 

 pedunculated gangUon-globules of Arion empiri- 

 corum, he was not aware of the large nuclei wliioh 

 they contained. 



4 See Helmholtz, De fabr. Syst. nerv. evert, loo. 

 cit. p. 10 ; Hannover, loc. cit. and fVill, in Mul- 

 ler^s Arch. 1844, p. 76.* 



1 For the descriptions and figures of the nervous 

 sj'stem of several Cejjhalophora, see Cuvier, Mem. 

 loc. cit. ; Garner, Trans, of the Linn. Soc. XVII. 

 p. 4S8 ; Rymer Jones, Cyclop, of Anat. p. 392, 

 Art. Gasteropoda ; Anderson, Ibid. III. p. 605, 

 Art. A^ervous System ; and Fan Beneden, Exer- 



CISGS ZOOti loc Cit T 



2 See Milne Edwards, Ann. d. Sc. Nat. XVIII. 

 1S42, p. 326, PI. XI., and Delle C/iiaje, Descriz. II. 



* [§207, note 4.] Leidy''s results, after very 

 careful dissection, do not accord with these, for he 

 observed none of the nerve-fibres originate or ter- 

 minate in the gangUonary globules ; see loc. cit. 

 vol. I. p. 243. — Ed. 



t [ § 208, note 1.] See also Alder and Hancock, 

 loc. cit. Part. H. PI. II. fig. 9 (Dendronotus), PI. 

 rV. fig. 16 (Doto) ; Part. III. PI. VIII. fig. 8 

 (Eolis); Part. IV. PI. V. fig. 1, k. {Scyllaea) ; 

 Part V. PI. n. fig. 13 (Doris), PI. XLIU. fig. 10 

 (Antiopa) ; then Leydig, Ueber Paludina vivi- 



20=* 



para, &c., loc. cit. p. 152, Taf. XIII. fig. 49, a. /^. 

 {Paludina) ; Blanchard, Ann. d. So. Nat. XI. 

 1849, p. 78, PI. III. fig. 1, PI. IV. fig. 1 {Janus) ; 

 Middendorff, loc. cit. p. 75, Taf. IX. {Chiton); 

 Leidy, loc. cit. PI. I. fig. I. 11-14 {Umax), PI. 

 IV. fig. V. 15-17 {Faginulus), PI. V. fig. I. 32, 33, 

 34 {Bulimus), PI. VI. fig. II. 25, PI. VH. fig. 

 VIII. 20, PI. IX. fig. rV. 26, 27, PI. X. fig. IV. 

 24, 25, 26 {Helix); PI. XIII. fig. IV. {Helicina), 

 PI. XIV. fig. IV. Pi. XVI. {Glandina). — Ed. 



