§209. 



THE CEPHALOPIIORA. 



235 



5. With other Apneusta, the oesophageal ring is composed of several 

 contiguous ganglia which closely bind the oesophagus, but have no appar- 

 ent commissures/"^ 



6. The other Gasteropoda, and especially the Pectinibranchia and 

 Pulmonata, have a highly-developed superior and inferior ganglionic mass ; 

 the oesophageal ring is formed by these ganglia, being connected on each 

 side by a cord, which is oftener double than single/**^ The superior mass 

 is composed usually of two ganglia which ai-e connected by a transverse 

 commissure, or are contiguous, and sometimes even blended together. '^^ 



The inferior mass also presents many variations. With some species it 

 consists of a circle of distinct ganglia, connected by commissures;^'"' while 

 with others, it is composed of a group of ganglia more or less fused 

 together.*^'' 



§ 209. 



With many of the Cephalophora,^' there is a Splanchnic nervoivs sij stein. 

 This can be divided into a Plexus splanchnicus anterior and posterior. 

 The first is composed usually of a double Ganglion pharyngeum inferius, 

 connected by a transverse commissure, or contiguous, but rarely blended 

 together. They are situated under the cesophagus and connect with the 

 cerebral mass by two filaments ; they send ofi" nerves principally to the 

 pharynx, to the cesophagus and the salivary glands ; and when the posterior 

 plexus is wanting, they send nerves also to the liver and the genital glands. '^> 



7 This oesophageal ring is composed of eight gan- 

 glia with Tergipes {Nordmann, loc. cit. p. 35, 

 Tab. II.), but with Actaeon, there are only seven, 

 the lower one of which, asymmetrical, sends two 

 very long cords of communication to two large 

 cerebral ganglia, while the two lateral ganglia con- 

 nect by a short commissure passing under the 

 oesophagus (AUman, loc. cit. p. 194, PI. VII. fig. 

 1). According to a communication which Kolliker 

 has made to me, this ring, with Flabellina, has 

 only five ganglia. 



S See Berthold, in Miiller^s Arch. 1835, p. 3Y8. 



9 There is a transversal commissure between the 

 two cerebral ganglia with Patella, Haliotis, Pha- 

 sianella, Janthina, Turbo, Paludina, Lymna- 

 eus, PlaiiorOis, and with many other species having 

 a shell. These two ganglia are contiguous with 

 Helix, Limax, and Cypraea ; but they are fused 

 into one with Buccinum, Murex, Oliva, Harpa, 

 Valuta, and other Pectinibranchia. 



10 Haliotis has two, and Patella four inferior 

 ganglia disposed transversely, which send off 

 from each side a double cord of communication to 

 the brain. With Ancylus, Lymnaeus, Planor- 

 bis, Physa, Succinea, BuUmus, the inferior por- 

 tion is composed of five to seven ganglia, unetiual and 

 disposed asymmetrically, and comiected together by 



off eight pairs of nerves ; Part V. PI. II. fig. 13 

 (Doris), cerebral ganglia, five pairs, and a single 

 ganglion, — the pairs are symmetrically placed 

 with regard to the median line and give off fifteen 

 pairs of nerves ; the single or visceral ganglion 

 gives off four nerves which are distributed to the 

 organs of reproduction, to the stomach, to the two 

 hearts, and to the branchiae, and can be traced 

 into ganglia of the sympathetic system belonging to 

 these several organs ; Part V. PI. XLIII. fig. 10 

 (^Antiopa), cerebral ganglia, six, and give off tea 

 or eleven pairs of nerves. 



commissures ; see Berthold, loc. cit., and my ob- 

 servations in fViegmariri's Arch. 1841, I. p. 153, 

 Taf. VI. fig. 3 {Lymnaeus stagnalis). Judging 

 from the figure of Van Benedcn (Exercices zoot. 

 loc. cit. Fasc. I. Mem. sur le Lymnaeus gluti- 

 nosus, p. 30, PI. I. fig. 12, and Ann. d. Sc. Nat. 

 VII. 1837, p. 112, PI. III. B.), of the oesophageal 

 ring of Amphipeplea, this genus resembles, in this 

 respect, Lymnaeus. With Pneumodermon vio- 

 laceum (Van Beneden, loc. cit. p. 45, PI. I. fig. 2), 

 and with Clio (Eschricht, loc. cit. p. 6, Tab. III. 

 fig. 28), the lower portion appears also to consist 

 of a circle of ganglia. 



11 Helix, Limax, Arion. With Limax (Pou~ 

 chet, Recherch. loc. cit. p. 8), there remains in the 

 middle of the fused ganglia only a small opening, 

 which, with several species ol Helix, entirely disap- 

 pears.* 



1 See Brandt, Ueber der Mundmagennerven der 

 Evertebraten, loc. cit. p. 43. 



2 The two ganglia of the Plexus splanchnicus 

 or Sympathicus anterior, which is situated more 

 or less in front of the inferior portion of the oesoph- 

 ageal ring, have, together with their correspond- 

 ing nervous filaments, already been regarded 

 by Cuvier as a sympathetic system, with several 

 Gasteropoda ; see his Mem. sur le Genre Aply- 



With all these genera, the oesophageal ring is 

 formed by lateral commissures which unite with the 

 sub-oesophageal ganglia which are sometimes two 

 (Dendronotus, Doto, Eumenis), sometimes four 

 {Eolis, Doris, Antiopa). — Ed. 



* [§ 208, note 11.] The nervous system of the 

 terrestrial Gasteropoda has been most carefully 

 described and beautifully figured by Leidy (loc. 

 cit.). The details are so full that I can only indi- 

 cate the work. — Ed. 



