§$ 188. THE ACEPHALA. 197 
With the Salpinae, the central nervous mass is upon the dotsal surface 
in front of the middle of the body. It consists of many closely-aggre- 
gated, yellowish ganglia, from which nerves pass off 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 cesophagus, it may be concluded that it is analogous to that of the 
Lamellibranchia. © 
3. With the Lamellibranchia, the nervous system is the most distinct.” 
Its very symmetrical arrangement is prominent, except in the unequivalved 
species. 
1 Meyen was the first to describe with care this 
mervous mass with Salpa; for, before him, many 
other parts of the animal had been erroneously 
taken by Savigny (Mém. &c. II. p. 127), and 
Chamisso (De Salpa, &c., p. 5), for the nerves and 
ganglia ; see Meyen, Nov. Act. Acad. Leop. loc. 
cit. p. 394, Tab. XXVII. fig. 5, d. 18 (Salpa pin- 
nata), Tab. XXVIII. fig. 5, hk. 12 (Salpa mucro-~ 
nata). Quoy and Gaimard have also observed a 
central nervous system in the dorsal region of sev- 
eral Salpa; see Voyage de l’Astrolabe, Zool. III. 
p. 559, and the Atlas zoologique of the same, Mol- 
lusques, Pl. LXXXVI.; or Isis, 1886, p. 113, Tab. 
WL 
Eschricht’s description is still more minute ; but 
he has taken for the ventral surface that portion of 
the body in which this lobulated ganglionic mass is 
situated ; see his Memoir, Over Salperne, &c., p. 
12, Tab. IL. fig. 8,10, u,v. (Sadpa cha bila ee 
and Tab. III. fig. 22 (Salpa zonaria). , also, 
Delle Chiaje, Descriz. &e. III. p. 45, Tav. 
LXXVIIL. fig. 8, n. 12 (Salpa marina). I am 
yet undecided whether the nervous ring, which, 
according to Eschricht, is formed by the junction of 
the two nerves surrounding the anterior respiratory 
*orifice, really corresponds to the I J ring. 
2 A very detailed description accompanied with 
figures of the nervous system of the simple Asci- 
diae, may be found in the works of Cuvier (Sur 
les Ascididés, &c., loc. cit. p. 24, Pl. IL. fig. 2 c. 5, 
g. IIL. fig. 2, 3 c. (Cynthia and Phallusia)) ; 
Eschricht (Beskrivelse af Chelyosoma, loc. cit. p. 
8, fig. 4, ¢.); Delle Chiaje (Descriz. &c. IL. p. 
28, Tav. LXXXII. fig. 2, and LXXXIV. fig. 3, 5, 
(Phailusia)) ; and Savigny, who has included also 
the compound Ascidiae (Mém. &c. p. 32, Pl. IX. 
fig. 2% XI. fig. 1. D*. (Phallusia); also Pl. 
XXL. fig. 15. XXII. fig. 14. XXIII. fig. 18. De. ds 
<(Botryllus and Pyrosoma)). 
The principal ganglionic mass is always nearer 
the anal than the oral tube, and does not give off 
branches except at its extremities. The nervous 
wing of the Ascidiae, has been observed by both 
Cuvier, and Delle Chiaje. 
The 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. Rend. XXXIV. 1852, p. 665, and XXXV. 
1852, p.119; also, Frey and Leuckart, loc. cit. 
17* 
regards as the brain ; while he has given the name 
of Ganglion sympathicum to a principal gangli- 
onic mass, lying near the anal tube. 
8 Cuvier (Sur la Lingula, 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 cesopha- 
gus of Orbicula, and one behind it ; and also two 
nerves arising from the two anterior ganglia ate 
tended with two arteries which go to the two hearts, 
4The nervous system of the Lamellibranchia 
was discovered by J. Rathké. In 1797, he had 
well represented the anterior pair of ganglia of An- 
odonta (loc. cit. p. 162, Tab. IX. fig. 10,11). Poli, 
it is true, had already figured the nervous system 
of several species of this order (loc. cit. Tab. 
XXXVI. fig. 1,n. (Pinna); Tab. VIII. fig. 1, i. 
(Pholas) ; Tab. TX. fig. 10, a. (Unio) ; Tab. X. fig. 
“15, Tab. XI. fig. 1, Tab. XIII. fig. 6, (Solen) ; Tab. 
XXV. fig. 1,(Area) ; Tab. XXXII. fig. 18, 1. (My- 
tilus)). But he err ly took it for a lymphati 
system. 
The following works may be consulted upon this 
system: Mangili, Nuove ricerche zoot. sopra 
alcune specie di conchiglie bivalvi, Milano, 1804 
(translated in Reid’s 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, 
Pl. XXIV. (Ostrea, Pecten, Modiola, Mactra, 
Mya, and Pholas); and, On the Anatomy of the 
Lamellibranch. loc. cit. p. 89, Pl. XIX. fig. 5 (Ve- 
nerupis); Keber, De Nervis Concharum, Diss. 
Berolini, 1837 ; Duvernoy, Sur animal de ’On- 
guline, in the Ann. des. Sc. Nat. XVIII. 1842, p. 
118, Pl. V. B. fig. 8 ; and, Sur le Systeme nerveux 
des Mollusques Acéphales bivalves, in the Comp. 
rend. 1844, Nos. 22, 25, 1845, No. 8 ; or in Froriep’s 
neue Not. 1845, No. 731; Blanchard, Observ. sur 
le Systéme nerveux des Mollusques ‘Acéphales testa- 
cés ou Lamellibranches, in the Ann. des Sc. Nat. 
Ii. 1844, p. 321, Pl. XII. and in Froriep’s neue 
Not. No. tal (Solen, Mactra, and Pecten); and 
John Anderson, Art. Nervous System, in the Cy- 
clop. of Anat. IIL. p. 604.* 
p. 46; Deshayes, loc. cit. p. 69, Pl. VIM. IX.; 
and Quatrefages, loc. cit. p. 63, Pl. I. fig. 3, 6 
(Teredo). — Ep. 
