238 THE CEPHALOPHORA. $ 211. 
single this otolite is spherical and crystalline, but when multiple they are 
fusiform, a little compressed, and usually very numerous, there being with 
some Gasteropoda, thirty or forty, and even eighty in each capsule.” 
The movements of these bodies are even more marked with the Cephal- 
ophora than with the Acephala; and the balancing and rotation of each, 
producing a kind of trembling of their whole mass which occupies the cen- 
tre of the capsule, is a wonderful spectacle. It has been recently discov- 
ered that these motions are due to very small cilia upon the internal surface 
of the capsule. 
The situation of these two auditive capsules varies according to the 
orders, families, and genera. With several Heteropoda, and Apneusta, 
they lie a little under the skin, behind the eyes, and are connected with the 
cerebral mass by a longer or shorter auditive nerve. In some Nudi- 
branchia, they lie upon the cerebral mass itself, contiguous with the pos- 
terior part of the eyes.© With the other Cephalophora, they are situated 
at the lower side of the body, and usually touch the inferior portion of the 
esophageal ring. 
fo} 3 
In only.a very few of the genera are the two auditory 
nerves separated and distinct from each other. 
Phasianelia, and Rissoa. I have myself seen 
them quite early in the embryos of Vermetus.* 
* 2 There is a single otolite only with the Hetero- 
poda, the Tubulibranchia and several of the Ap- 
neusta ; see Dedle Chiaje, Descriz. &c. II. p. 100, 
Tav. LXIII. fig. 5, 6 (Carinaria), and Quatre- 
‘ages, Ann. d. Sc. Nat. I. 1844, p. 160, Pl. VI. fig. 
-10 (Actaeon, Pelta, Chalidis). According to 
Krohn’s and my own observations, there are 
groups of small fusiform otolites with some Ptero- 
poda, and very many of the Gasteropoda, as Cym- 
bulia, Hyalea, Doris, Tritonia, Thetis, Aeolis, 
Venilia, Pleurobranchaea, Paludina, Planorbis, 
Lymnaeus, Helix, Limaz, and many others. It 
is not rare to find among these fusiform otolitez, 
others composed of two or four calcareous corpus- 
cles. Those of a spherical or spindle shape divide, 
from pressure, into four to eight fragments in the 
direction of cruciform lines which may often be seen 
before division. According to the observations of 
Laurent, Krohn, and myself, in the centre of 
these bodies, a single otolite is first developed, in the 
capsules which are to contain several, and others 
are added as the embryo increases ; see Frey, in 
Froriep’s neue Not. XXXVII. No. 801, p. 182, 
and Wiegmann’s Arch. 1845, I. p. 217. Taf. IX.t 
3 A priori, it might have been inferred that these 
motions are due to cilia, for the otvlites never come 
in contact with the sides of the capsule, but al- 
* ( § 211, note 1.] See also Alder and Hancock 
loc. cit. Part II. Pl. II. fig. 11 (Dendronotus), Pl. 
IV. fig. 18 (Doto); Part. III. Pl. VIII. fig. 4, 5, 
6 (Aeolis); Part V. Pl. II. fig. 15 (Doris); then 
Leydig, Ueber Paludina vivipara, &c., loc. cit. p. 
189, 155, Taf. XI. fig. 12, k. Taf. XIII. fig. 14-24, 
49, R. (Paludina) ; and Leidy, loc. cit. p. 246, Pl. 
IX. fig. VIL-IX. (Helix), Pl. XIII. fig. IV. 4 
(Helicina). Leydig has furnished valuable con- 
tributions in the development of this organ ; in Pa- 
ludina, it appears, prior to the nervous system 
with which it is connected, as an almost solid body 
with a very small, round, central cavity ; with the 
growth of the organ, this cavity increases, and 
finally the whole becomes a capsular organ in which 
are developed otolites. — Ep. 
ways remain at a little distance from it, and when 
there are several,they are grouped in the centre ; 
indeed when one has strayed from this central: po- 
sition it is always quickly returned. Wagner 
(Lehrbuch der Physiol. ed. II. 1843, p. 463) positive- 
ly affirms that he has seen cilia in these capsules. 
They have been very distinctly seen by Kélliker 
also (loc. cit.) with T'ritonia, Thetis, Pleuro- 
branchaea, Diphyllidia, Hyalea, Lissosoma, and 
Rhodope. 
4 See Laurent, loc. cit. fig. 1-6, and Quatre- 
fages, Ann. d. Sc. Nat. I. loc. cit. Pl. IV. VI. Ac- 
cording to Delle ciae (Descriz. &c. loc. cit. Tav. 
LXIII. fig. 3, d. 14, f£.), and Milne Edwards 
‘Anm & Se Nat. XVIII. 1842, Pl. XI. fig. 1, z. 
fig. 3, h.), the auditive nerves are very Jong with 
Carinaria. With many Cephalophora which are 
transparent, the auditive organs may be perceived 
by the naked eye, through the skin, as two white 
spots.t 
5 Doris, Thetis, Tritonia, Aeolis (Krohn, loc. 
cit.), and Tergipes (Nordmann, loc. cit. p. 44, 
Tab. II.). 
6 According to Krohn (loc. cit. No. 394, p. 311) 
the two auditive capsules of Pleurobranchaea, and 
Paludina receive distinct auditive nerves from the 
inferior portion of the cesophageal ring. He has 
observed the same with Cymbulia, and Hyalea 
(loc. cit. No. 306, p. 311); but Van Beneden (Ex- 
ey 
t [§ 211, note 2.) See, for the auditory appara- 
tus of Aeolis, Hancock and Embleton, Ann. Nat. 
Hist. 1849, III. p. 196. The otolites which have 
hitherto been regarded calcareous, they found not 
to be materially affected by long treatment with 
acetic acid. — Ep. 
+ [§ 211, note 4.] See also Leydig (Anat. Be- 
merk. tib. Carinaria, Firola und Amphicora, in 
Siebold and Kiélliker’s Zeitsch. III. 1851, p. 325). 
His Taf. IX. fig. 4 (Carinaria) gives a very clear 
idea of the structure and relations of the auditory 
capsules with these animals. His observations 
upon the cause of the movements of the otolites are 
confirmatory of those of Milne Edwards with 
Firola ; see L’Instit. Jour. univ. des Soc. sav. XTIT. 
1845, p. 43.— Ep. 
