THE ACEPHALA. 201 
§ 186. 
As yet, organs of hearing with the Acephala have been found only among 
‘the Lamellibranchia. They are here feebly developed, consisting only of 
two simple round capsules filled with a transparent liquid. Their very thick 
and somewhat solid walls are homogeneous and transparent; they enclose a 
vitreous spherical otolite, of a crystalline structure,” and composed of car- 
bonate of lime. These otolites constantly keep up very singular swing- 
ing and rotatory motions, which instantly cease, however, when the capsule is 
ruptured.” These auditory capsules when present, are situated in the foot 
‘in front of the pedal ganglia with which they always communicate, either 
contiguously, or by two auditory nerves which they receive. 
§ 187. 
Organs of vision are very common with the Acephala, and always many 
in number. With some, they occupy a large portion of the borders of the 
amantle; with others, they are confined to the external orifices of the longer 
$$ 186, 187. 
or shorter mantle-tubes. 
4 These organs were first noticed by me with the 
‘Najades, Cardiacea, and the Pyloridae ; but were 
regarded as of a doubtful nature. Since then, after 
scomparing them with the auditory organs of the 
embryos of fish, I am satisfied that they are really 
‘very simple organs of hearing ; see Muller's Arch. 
1838, p. 49, and Wiegmann’s Arch. 1841, I. p. 148, 
‘Taf. VI. fig. 1, 2 (Cyclas cornea) ; or, the Ann. d. 
Sc. Nat. X. 1838, p. 319, XIX. 1843, p. 193, Pl. 
II. B. It appears, moreover, that similar corpus- 
«oles are found in other orders of these animals. 
Thus, Delle Chiaje mentions with Salpa neapoli- 
tana, an organ situated above the nervous centre 
which exactly resembles the auditory capsules I 
chave discovered in the foot of Cyclas. Unfortu- 
nately he has neither figured nor carefully described 
this organ (Descriz. &c. III. p. 45, Tav. LXXVI. 
fig. 1,1.). Eschricht (Anat. Beskriv. af Chelyo- 
‘soma Macleayanum, p. 9, fig. 4, 6, d. y. and fig. 5) 
has also regarded as an auditory organ a remarka- 
ble apparatus which he found near the nervous cen- 
tre of a simple Ascidian. This consists of a pyri- 
form vesicle filled with whitish matter, and of a 
clavate body which has, upon its large end, a fis 
sure and two lateral depressions. 
Delie Chiaje’s figure (Descriz. &c. IIT. Tav. 
LXXXII. fig. 4.), of the principal ganglionic mass 
of Cynthia papillata, reminds me of the cla- 
vate body of Chelyosoma and leads me to think 
that this author has confounded it with the nervous 
centre, I think that this organ exists generally 
with both the simple and compound Ascidiae, for 
Savigny has noticed with Cynthia, Phallusia, 
Aplidium, Polyclinum, Botryllus, Eucoelium, 
Synoecium, Pyrosoma, &c., two tubercles near the 
nervous ring which surrounds the respiratory tube 
(Tubercule antérieur et postérieur). And, to 
judge from his figure (Mém. &c. Pl. VI. fig. 1%, 2, 
42, h. Pl. VIL. fig. 2"), of one of these tubercles, with 
Cynthia, these organs appear analogous to the cla- 
vate body just mentioned. At all events, these 
tubercles deserve, with Zootomists, more attention 
than has hitherto been given them. 
2 These motions are probably due to the ciliated 
epithelium lining the cavity of the capsules ; see, 
‘below, the auditory organs of the Gasteropoda. 
8 I have been unable as yet to find these capsules 
with the apodal Lamellibranchia, — at least, with 
Tichogonia, and Mytilus. They appear to exist, 
however, for recently Deshayes has found them both 
an Teredo. Here they were situated at the extrem~ 
ity of the septa lying between the pericardium and 
the elevator of the anus, and upon which the ante- 
rior extremity of the branchiae is inserted ; see 
Comp. rend. 1846, XXII. No. 73 or Froriep’s 
neue Not. No. 813, p. 323. 
4 With Cyclas, and Tellina, the auditory cap- 
sules are contiguous with the ganglia of the Par 
pedale. With Anodonta, Unio, Cardium,' and 
‘Mya, they are a little removed. 
It is remarkable that these organs appear very 
early in the embryos of certain Lamellibranchia 
(Cyclas), while in others (Anodonta and Unio), 
no trace of them is seen during the embryonic 
life. 
1 Poli (loc. cit. IT. p. 158, 107, Tab. XXII, fig. 
1,4; and Tab. XXVII. fig. 5, 14, 15), was the 
first to compare to human eyes these remarkable 
bodies, which, brilliant as diamonds, lie upon the 
borders of the mantle of Pecten and Spondylus, 
with this expression: Ocelli smaragdino coiore 
coruscantes. Nevertheless, it is only of late that 
these organs have received much attention. Gar- 
ner (On the Anat. of the Lamellibr. Conchifer. &c. 
Pl. XIX. fig. 1, c. 3) was the first to notice anew 
the Ocelli of Pecten. Grant (Outlines, &c., p- 
258) has described those of Pecten and Spondylus 
as organs long known. Grube (Miiller’s Arch. 
1840, p. 24, Taf. III. fig. 1, 2), and Krohn (Ibid. 
p. 381, Taf. IX. fig. 16) have described the struc- 
ture of these organs, and, quite recently, Will (Fro- 
riep’s neue Not. 1844, No. 622, 623) has treated 
this subject most profoundly. 
Deshayes is not satisfied of the existence of or- 
gans of vision with the Pectinea, while Duvernoy 
regards as such the bodies situated on the border 
of their mantle (Instit. 1845, p. 52, 88). It is astonish- 
ing that Deshayes should have denied eyes to the 
Pectinea, where they are so complete. He could have 
better denied them to Phallusia, Arca, Ostrea, and 
other Acephala. During my last visit at Venice 
and at Trieste, I examined living individuals of the 
genera Arca, Ostrea, Pinna, as well as other Lam- 
ellibranchia and various Ascidiae ; but with all 
possible care, I was unable to verify Will’s descrip 
tion (loc. cit.) of the eyes of these animals. In 
most cases, the bodies which he has described as 
eyes, have appeared to me only as simple excres- 
cences of the mantle, which are variously colored, 
but are wholly without the indispensable optic ap- 
paratus for a visual organ. 
