«^183. 



THE ACEPHALA. 



197 



"With the Salpinae, the central nervous mass is upon the dorsal surface 

 in front of the middle of the body. It consists of many closely-aggre- 

 gated, yellowish ganglia, from which nerves pass oflF in all directions. <'' 



With the Ascidiae, it consists of a single large ganglion, which is easily 

 found within the muscular envelope, in an angle formed by the oral and anal 

 tubes. The nerves which pass off in different directions from this gan- 

 glion, belong chiefly to the muscular envelope. Some of them, however, 

 pass to the organs of sense situated near the two respiratory tubes, and form 

 around the orifice of that one of them which is buccal also, a complete cir- 

 cle which corresponds perhaps to an oesophageal ring.'-' 



2. The nervous system of the Brachiopoda is as yet little known. 

 However, from the presence, in some species, of two or three ganglia about 

 the oesophagus, it may be concluded that it is analogous to that of the 

 Laniellibrauchia. '"' 



o. With the Lamellibranchia, the nervous system is the most distinct.''*' 

 Its verj- symmetrical arrangement is prominent, except in the unequivalved 

 species. 



1 Meyen was the first to describe with care this 

 nervous mass with Salpa ; for, befoi-e him, many 

 other parts of the animal liad been erroneously 

 taken by Savii^ny (Mem. kc. 11. p. 127), and 

 Chamisso (Do Salpa, &c., p. 5), for the nerves and 

 ganglia ; see Meyen, Nov. Act. Acad. Leop. loc. 

 cit. p. 391, Tab. XXVII. fig. 5, d. 18 {Salpa pin- 

 iiala). Tab. XXVIII. fig. 5, h k. 12 {Salpa mucro- 

 nata). ^uoy and Gaimard have also observed a 

 central nervous system in the dorsal region of sev- 

 eral Salpa ; see Voyage de 1' Astrolabe, Zool. III. 

 p. 559, and the Atlas zoologique of the same, Mol- 

 Jusqucs, PI. LXXXVI.; or Isis, 1836, p. 113, Tab. 

 VI. 



EschrichVn description is still more minute ; but 

 lie has taken fur the ventral surface that portion of 

 the body in which this lobulated ganglionic mass is 

 situated ; see his Memou-, Over Salperne, &c., p. 

 12, Tab. II. fig. 8, 10, ii, v. {Salpa cordiformis), 

 and Tab. III. tiy. 22 {Salpa zonarid). See, also, 

 Delle Chiajc, Descriz. &c. III. p. 45, Tav. 

 LXXVIII. fig. 3, n. 12 {Salpa maxima). I am 

 yet undecided whether the nervous ring, which, 

 according to Eschricht, is formed by the junction of 

 the two nerves surrounding the anterior respii'atory 

 orifice, really corresponds to the oesophageal ring. 



2 A verj- detailed description accompanied with 

 figures of the nervous system of the simple Asci- 

 diae, may be found in the works of Cuvier (Sur 

 les Ascidies, &c., loc. cit. p. 24, PI. II. fig. 2 c. 5, 

 g. in. fig. 2, 3 c. {Cynthia and Phalluaia)) ; 

 Eschricht (Bcski-ivelse af Chelyosoma, loc. cit. p. 

 S, fig. 4, c.) ; Delle Chiaje (Descriz. &c. III. p. 

 2S, Tav. LXXXII. fig. 2, and LXXXH'. fig. 3, 5, 

 (Phallusia)) ; and i'aujVny, wlio has included also 

 the compound Ascidiae (Mem. kc. p. 32, PI. IX. 

 tig. 22. XI. fig. 11. D'. {Phallusia); also PI. 

 XXI. fig. li. XXn. fig. 11 XXIII. fig. 18. D-. d-. 

 {Jiotryllus and Pyrosoma)). 



The principal gangUonic mass is always nearer 

 the anal than the oral tube, and does not give off 

 branches except at its e.xtremitics. The nervous 

 ring of the Ascidiae, has been observed by both 

 C'?/i ier, and Delle Chiaje. 



Tlie last of these authors has also mentioned a 

 particular ganglion which he has observed with 

 Phallusia mamillaris, in this ring, and which he 



* [ § 183, note 4.] See, also, Duvernoy (suite) 

 Compt. Kend. XXXIV. 1852, p. 66.5, and XXXV. 

 1852, p. 119 ; also, Frey and Leuckart, loc. cit. 



17# 



regards as the brain ; while he has given the nama 

 of Ganglion sympathicum to a principal gangli- 

 onic mass, lying near the anal tul>e. 



3 Cuvier (Sur la liugula, loc. cit. p. 8) thinks 

 he has observed two ganglia at the base of the 

 arms, but which give off no nerves. Owen (loc. 

 cit.) has found two ganglia in front of the oesopha- 

 gus of Orbicula, and one behind it ; and also two 

 nerves arising from the two anterior ganglia at- 

 tended with two arteries which go to the two hearts. 



i The nervous system of the Lamellibi-anchia 

 was discovered by J. Rathke. In 1797, he had 

 well represented the anterior pair of ganglia of An- 

 odonta (loc. cit. p. 162, Tab. IX. fig.'lO, 11). Poll, 

 it is true, had already figm-ed the nervous system 

 of several species of this order (Ifx;. cit. Tab. 

 XXXVI. fig. 1, n. {Pinna); Tab. VIII. fig. 1, i. 

 (Pholas) ; Tab. IX. fig. 10, a. {Unio) ; Tab. X. fig. 

 15, Tab. XI. fig. 1, Tab. XIII. tig. 6, {Soleii) ; Tab. 

 XXV. fig. 1, {Area) ; Tab. XXXII. tig. 18, r. {3Iy- 

 tilus)). But he erroneously took it for a lymphatic 

 system. 



The following works may be consulted upon this 

 system : Mangili, Nuove ricerche zoot. sopra 

 alcune specie di conchiglie bivalvi. Milano, 1804 

 (translated in ReiCs Arch. IX. 1809, p. 213, Taf. 

 xb. {Anodonta)); Brandt, Medizin.Zool. II. p. 310, 

 Taf. XXXVI. fig. 10,-12 (of the Oyster) ; Garner. 

 On the Nervous System of Molluscous Animals, in 

 the Trans, of the Linn. Soc. XVII. 1837, p. 485, 

 PI. X.XIV. {Ostrea, Pecten, Modiola, Mactra, 

 Mya, and Pholas); and, On the Anatomy of the 

 Lamellibranch. loc. cit. p. 80, PI. XIX. fig. 5 {Ve- 

 nerupis); Keber, De Nervis Concharum, Diss. 

 Berolini, 1837 ; Duvernoy, Sur I'animal de TOn- 

 guline, in the Ann. des. Sc. Nat. XVIII. 1842, p. 

 118, PI. V. B. fig. 8 ; and, Sur le Syst^me nerveux 

 des Mollusques Acephales bivalves, in the Comp. 

 rend. 1844, Nos. 22, 25, 1845, No. 8 ; or in Froriep'i 

 neue Not. 1845, No. 731 ; Blanchard, Observ. sur 

 le Systeme nerveux des Mollusques Acephales testa- 

 ces ou Lamellibranches, in the Ann. des Sc. Nat. 

 III. 1844, p. 321, PI. XII. and in Froriep's neue 

 Not. No. 741 {Solen, Mactra, and Pecten) ; aad 

 John Anderson yAvt. Nervous System, iu>the Cy- 

 clop, of Anat. lU. p. 604.* 



p. 46; Deskayes, loc. cit. p. 69, PI. VIII. IX.; 

 and (^uatrefages, loc. cit. p. 63, PI. I. fig. 3, 6 

 {Teredo). — Ed. 



