§ 212. THE CEPHALOPHORA. 2939 
§ 212. 
The organs of Vision are absent with only a very few genera of the Ce- 
phalophora.® They are never more than two in number, and their size, com- 
pared to that of the body, is usually small; they are smallest with some 
Heterobranchia, and the largest with the Pectinibranchia.~ 
The eyes consist usually of two round bulbs concealed under the skin ; 
this last is colorless at this point, and lies over them likea thin lamella. Hach 
bulb is limited outwardly by a tissue resembling a Sclerotica, but beneath the 
skin, this tissue is more convex than elsewhere, and thus forms a kind of Cor- 
nea.” The sclerotica is lined by a dark pigment layer, or Choro.dea, which, 
near the corner, ends in a free border, forming thus a Pupilla. With some 
‘Gasteropoda, the pupillary border has a very thick pigment layer which 
serves, perhaps, as an Iris. 
The internal surface of the choroidea is covered by a whitish pellicle 
which undoubtedly is a Retina, for the optic nerve enters the sclerotica at 
4 point opposite the cornea.” The cavity of the eye-bulb is filled with a 
gelatinous, vitreous body, which, in front, envelops a spherical crystalline 
Tens.© 
The Optic nerve arises from the cerebral ganglia, and runs along, for a 
longer or shorter distance, in company with the tentacular nerve of the 
same side.” 
ere, zoot. Fasc. II. p. 13, Pl. I. fig. 8, f. 9, c. 10, 
Pi. V. fig. 13, x.) affirms that with the first of these 
genera, and with Tied nia, and Li: ina, the 
auditive vesicles lie directly upon the two principal 
inferior ganglia; this agrees with Delle Chiaje’s 
description of these organs with Cymbulia ; see his 
Descriz. &c. I. p. 94, Tav. XXXII. fig. 2, i. 
Eschricht (loc. cit. p. 6, Tab. IIL. fig. 28, s.) has 
figured, with a Clio, two ganglia with short pe- 
duncles, situated close by the two anterior ganglia 
of the cesophageal ring. These, I infer, are only 
the auditive capsules receiving two short auditive 
nerves. 
With those Gasteropoda whose inferior cesophageal 
ganglia are arranged ina circle, as, for examples, 
with Lymnaeus, Planorbis, Physa, Succinea, 
Bulimus, Ancylus, these capsules lie upon the 
posterior surface of the two large anterior ganglia. 
But when, on the other hand, these ganglia are 
-approximated, or even fused into one common mass, 
as with Hediz, these capsules lie upon the inferior 
-surface of this mass, and especially upon the 
nodules correspouding to two large anterior ganglia. 
1 Phyllirrhoé, Diphyllidia, Chiton, Dentali- 
um, and the Pteropoda with the ion of Sa- 
1829, p. 208, Taf. VI. fig. 4-8, and Ann. d. Sc. 
Nat. XXII. 1831, p. 7, Pl. ILI. IV., or in the Isis, 
1835, p. 347, Taf. VII. ), and Krohn (Millers 
‘arch. 1837, p. 479, 1839, p. 332, Taf. X. fig. 6-8) 
upon the eyes of Helix, Murez, Paludina, and 
Pterotrachea. 
8 The eyes of the Heteropoda present a remark- 
able exception; their very convex cornea is sur- 
rounded by a collar of skin ; the ocular bulb is very 
long, and, at its base, the sclerotica spreads out 
interiorly and posteriorly, forming a round prom- 
inence ; see Milne Edwards, Ann. d. Sc. Nat. 
XVIII. 1842, Pl. XI. fig. 1, c. (Carinaria), and 
especially the description of Krohn (loc. cit. 1839) 
of the eye of Plerotrachea. The ocular bulb of 
Clio is also very long, but has no prominence ; see 
Eschricht, loc. cit. p. 7, Tab. III. fig. 29. Those 
of Actaeon are long and pyriform; see Quatre- 
Sages, Ann. d. Sc. Nat. I. 1844, Pl. VI. fig. 5, and 
Allman, loc. cit. Pl. VII. fig. 2. 
4 Adark iris is distinctly seen with Paludina 
and Murex. That of Strombus is very brilliant 
and multicolored, according to Quoy and Gai- 
mard ; see, Voy. de P Astrolabe, Zool. ILI. p. 56, Mol- 
Pil. L. I am not yet certain whether 
gitta and Clio, are blind. In many of the Ptero- 
poda, the auditive appear to have been taken for 
the ocular organs. 
2 Swammerdamm (Bibel der Nat. p. 47,Tab. IV. 
fig. 5-8) made out very correctly the structure of the 
eyes of Helix. The later works of Stiebel (Meck- 
el’s Deutsch. Arch. 1819, p. 206, Tab. V.), Huschke 
Beitr. zur Physiol. u. Natur; gesch. 1824, p. 57, 
Taf. III. fig. 8), and of De Blainville (De Porgan- 
isat. des Animaux, 1823, p. 445), upon the eyes of 
Helix, Paludina, and Foluta, have been much 
‘improved by those of Miller (Meckel’s Arch. 
* [§ 212, note 4.) For the visual organs of Pa 
dudina, with histological details, and especially 
confirmatory of Krohn’s observations, see Leydig, 
floc. cit., Siebold and Kélliker’s Zeitsch. II. 1850, 
or not the iris of these Gasteropoda is susceptible 
of movements of contraction and dilatation. It 
may be well to add that the choroidea of the He- 
teropoda has several spots of its surface free from 
pigment.* 
5 Krohn (loc. cit. 1837, p. 482) affirms that he 
has seen this white layer with a Paludina. 
6 The existence of a distinct vitreous body was 
known to Swammerdamm,and has been confirmed 
by Krohn (loc. cit. 1837). 
7 According to Krohn (loc. cit. 1839), the two 
optic nerves of Paludina, Murex, Aplysia, Cy- 
p. 159, Taf. XII. fig. 25, Taf. XIII. fig. 26-28. 
See also this same author in Siehold and Kélli- 
ker’s Zeitsch. 1861, IIL. p. 327 (Carinaria).— Ep. 
