162 THE ANNELIDES. $ 151. 
enveloped with a layer of black pigment.© Each of these bodies receives 
a nervous filament from the cerebral ganglion. Undoubtedly, these fila- 
ments are optic nerves, and the cylindrical bodies are light-refracting and 
light-concentrating organs. 
Many of the Dorsibranchiati are entirely without eyes, having only the 
eye-specks ; but others, belonging to the Amphinomae, Nereideae, Huniceae, 
and Aphroditae, have two to four very distinct eyes.” In these, there is 
an eye-ball invested with a black or brown pigment layer: and this layer 
often has, above, a very distinct round pupillary opening, covered by the 
skin, which bulges out like a cornea. At the central portion of this 
layer, there is concealed a transparent body, which is very probably sur- 
rounded by a retina-like expansion of the optic nerve. The optic nerves 
which are given off usually from the upper surface of the brain have, after 
a short course, and before entering the pigment layer of the eye, an enlarge- 
ment. It is said that with some the light-refracting body and the pupillary 
opening are wanting. In such cases, the eyes could only distinguish light 
from darkness. 
III. Organs of Hearing. 
§ 151. 
Although it has never been doubted that the Annelides can perceive 
sounds, yet it is of late only that the attention has been directed to the 
locality of the auditory organs. The two vesicles, which, with some Chae- 
topodes, are situated near the cesophageal ring, and contain crystalline 
bodies, may be regarded as simple Vestzbuda, containing many otolites.® 
5 Weber was the first to show that the black 
specks of Sanguisuga officinalis were really eyes 
(Meckel’s Arch. 1827, p. 301, Taf. IIT. fig. 24). 
‘This has been confirmed by Brandt (Med. Zool. I. 
p. 251, Taf. XXIX. A. fig. 10-12), and more re- 
cently, Wagner has discovered in the interior of 
the pigment layer, a transparent body, composed, 
he thinks, of two parts, a crystalline lens and a vit- 
reous portion; see Wagner, Lehrbuch, d. ver- 
gleich. Anat. 1835, p. 428 ; also Lehrb. d. speziellen 
Phys. 1843, p. 383, and, Icon. physiol. 1839, Tab. 
XXVIII. fig. 16. : 
6 Brandt has been able to trace the ten optic 
nerves of Sanguisuga officinalis from the brain 
even to the eyes (Med. Zool. loc. cit. p. 250, Taf. 
XXILX. B. fig. 2).* 
7 With Glycera, Aricia, Arenicola, and Cir- 
ratulus, the eyes are wanting. With Goniada, 
and Nephtys, there are only simple pigment specks 
upon the head. With Eunice, Phyllodoce, and 
Alciopa, there are two eyes ; and four with Vereis, 
Syllis, Hesione,and Amphinome. The genus Al- 
ctopa is well suited, from its large size, for the dissec- 
tion of these organs. 
3 For a most detailed description of the eyes of 
Nereis, we are indebted to Muiiller (Ann. d. Se. 
Nat. XXII. 1831, p. 22, Pl. IV. fig.6 10), and Wag- 
* [ § 150, note 6.] For further details on the ocu- 
lar organs of the Hirudinei, see Moquin-Tandon, 
loc. cit. Ed. 1846, p. 80, Pl. VIII. fig. 11. Accord- 
ing to him, they contain neither a lens nor a vitre- 
ous humor, and are only light-perceiving organs. 
See also Leydig (loc. cit. p. 129) who makes the 
“ollowing statement upon the nature of these bodies 
ner (Lehrb. d. Physiol. p. 383, and Icon. physiol 
Tab. XXVID, fig. 15). Wagner, who, formerly 
(Zur_vergleich. Physiol. d. Blutes, 1833, p. 55), 
could not, any more than Muller, perceive the 
light-refracting body, has at last seen it distinctly. 
For my own part, I can-confirm its presence in the 
two eyes of Eunice gigantea, which have a circu- 
lar pupil. According to Rathkée (De Bopyro et 
Nereide, p. 44, Tab. II. fig. 4, 5) the eyes of Ne- 
Trews pulsatoria and lobulata want the pupil, 
although it is present with those of Wereis Dumer- 
alii. According to Wagner, the pupil is wanting 
with the two posterior eyes, but is present with the 
two anterior ones, with most of the Nereideae. 
1 I have compared the swellings noticed upon the 
cesophageal ring of Arenicola, hy Grube and Stan- 
nius (see Wiegmann’s Arch. 1841, I. 166), to the 
auditory vesicles of Mollusks, and their contents to 
otolites ; since then, Quatrefages has recognized 
the presence of similar auditory organs containing 
many otolites with two species allied to Amphicora 
(Compt. rend. XIX. 1844, p. 195, and Ann. d. sc. 
Nat. 1844, II. p. 94). Frey and Leuckart (Beitr. 
&c. p. $1), after a very careful examination of the 
organs of drenicola, which I have regarded as aue 
ditive, have confirmed this opinion, 
with Piscicola: ‘They receive no nerve, neither 
do they contain a light-refracting body. I regard 
them as simple or wholly analog to the 
corresponding pigment dots on the pedal shield, 
with which they also correspond in color and dis- 
tribution.”— Ep. 
