236 THE CEPHALOPHORA. $ 210. 
The posterior plexus is composed of a single mass, rarely of two separate 
ganglia. It is situated under the digestive canal or between its coils, and 
from it pass off nerves to the intestine, the liver, and the genital glands, 
beside two cords of communication with the lower portion of the oesophageal 
ring. 
CHAPTER IV. 
ORGANS OF SENSE. 
§ 210. 
The Tactile organs of the Cephalophora consist of two to four contractile 
tentacles situated upon the head, or the anterior part of the back. They 
receive nerves of considerable size from the cerebral mass, which have some- 
times a ganglionic enlargement in the extremity of the tentacle. With 
some Gasteropoda these tentacles are hollow and button-like at their ex- 
tremity, and can be inverted like the finger of a glove.” 
sia, p. 23, Pl. IV. fig. 1, c.; sur la Lymnée, p. 
9, Pl. I. fig. 11, u.; sur ’Onchidie, p. 14, Pl. I. 
fig. 6,0. Brandt (Med. Zool. II. p. 328, Tab. 
XXXIV. fig. 11, 18) has described it with Helix 
pomatia ; Van Beneden (loc. cit.), with Amphi- 
peplea, and T'reviranus (Beobacht. aus. d. Zoot. 
und Physiol. p. 42, Taf. IX. fig. 60), with Limaw. 
See also the researches of Schlemm (Dissert. de he- 
pate ac bile crust um et ‘um quorun- 
dam, Berol. 1844, p. 22, Tab. I. fig. 2, 3), upon the 
hepatic nerves of Gasteropoda. Delle Chiaje also, 
has seen this plexus with Doridium and Pleuro- 
branchus (Memor. II. p. 123, Tav. X. fig. 7, p. 
and III. p. 158, Tav. XLL. fig. 8, p.). According 
to Garner (loc. cit.), there is a double Ganglion 
pharyngeum inferius with, also, Scyllaea, Doris, 
and Eolis. With Patelia, on the contrary, he 
found this anterior Plexus splanchnicus composed 
of three ganglia, two upon the sides, and the third 
median and a little behind. : 
According to Van Beneden (Exercices zoot. 
Fasc. I. p. 30, Pl. I. fig. 12, ¢.), there is a similar 
disposition with Amphipeplea. With the Hetero- 
poda, this plexus is highly developed, composed of 
two ganglia, from which pass off long cords of com- 
munication to the cerebral mass ; see Milne Ed- 
wards, Ann. d. Sc. Nat. XVIII. p. 327, Pl. XI. 
fig. 1,8. x. and fig. 2, e.f.; and Delle Chiaje, 
Descriz. &c. loc. cit. Tav. LXIII. fig 14, 1. and 
LXIV. fig. 11, d. (Carinaria and Pterotrachea). 
The Pteropoda also have this plexus; but its two 
ganglia are more or less intimately fused, and as 
the cerebral mass is here replaced by a simple col- 
lar, it does not connect with it, but with the infe- 
rior portion of the cesophageal ring ; see Van Be- 
neden, Exercices zoot. Fasc. II. p. 11, et seq. Pl. I. 
fig. 9, 10, IL. fig. 8, 10, III. fig. 6,9, and V. fig. 
* [§ 209, note 2.] For the splanchnic nervous 
system of the terrestrial Gasteropoda, see Leidy, 
loc. cit. Pl. XIII. fig. IV. 2 (Helicina), Pl XIV. 
fig. IV. 3 (Glandina), and Pl. XVI. fig. II. 2 
(Helix). 
See also for that of the Nudibranchia, Alder 
But with the 
18 (Cymbulia, Tiedemannia, Hyalea and Lima- 
cina.)* 
3 The Plexus splanchnicus posterior with its 
two long cords of communication is quite apparent 
with Aplysia (see Cuvier, loc. cit. p. 23, Pl. IV. 
fig. 1, R.). Delle Chiaje (Memor. Tayv. V. fig. 1, 
m, X. fig. 7,0. and XLI. fig. 8, y. y.), has observed 
it with Doridium, and Pleurobranchus, be- 
side the genus just mentioned, and in Pleuro- 
branchus, he found it composed of two entirely 
separated ‘ganglia. Van Beneden (Exerc. zoot. 
Fase. I. p. 46, Pl. I. fig. 3-5) has found it com- 
posed of only a single ganglion with Pneumoder- 
mon. Milne Edwards (loc. cit. p. 329, Pl. XI. 
fig. 1, u. v. 6), has observed in the visceral sac of 
Carinaria, first, a double Ganglion abdominale, 
which receives two long cords of communication 
from the cerebral mass and from the Ganglion 
pedale, and then 2 Ganglion anale, communi- 
cating with the two abdominal ganglia, : 
1 There are most usually two tentacles. But with 
Limaz, Arion, Heliz, Achatina, Clausilia, and 
other Helicina, there are four. They are wholly 
wanting with Sagitta, Cleodora, Cuvieria, Hya-. 
lea, Pterotrachea, Lissosoma, Rhodope, Phyl- 
Lidia, ahd Dentalium. i 
2 This swelling exists not only with the inferi- 
or and eyeless tentacles, but also the superior ones 
bearing eyes, with several Limacina and Helicina. 
However, no ganglionic globules are seen in it, and 
only a finely-granular substance lies interposed be- 
tween the primitive fibres. 
3 With the Limacina and Helicina, these organs 
are invested by a muscle which arises upon the 
columnella or upon the internal surface of the 
mantle, and is inserted at the extremity of each 
tentacle. 
\ 
and Hancock, loc. cit. (Eolis, Doris, Antio- 
Ppa, &e.). 
According to Middendorff (loc. cit. p. 76), Chi- 
ton has a complex splanchnic nervous system 
which is widely distributed over the digestive or- 
gans and their auxiliary glands. — Ep. 
