§ 211. 
THE CEPHALOPHORA. 
237 
majority of the Cephalophora, they are solid and usually conical, and some- 
times are replaced by two groove-like, cutaneous processes, which, from, 
contractions of their muscular fibres, can be shortened, but not inverted.“ 
Beside these tentacles, many Cephalophora have also as tactile parts, 
organs, which consist of two contractile lobes situated on each side of the 
cutaneous fold which rests over the mouth like a second lip.” The prehen- 
sile organs about the mouth of certain Pteropoda, and the contractile fila- 
ments and processes on the border of the mantle of other Cephalophora, are 
also used, probably, as tactile parts. 
§ 211. 
The organs of Hearing, which as yet have been found in all the orders 
of these animals, are, as in the Acephala, of a very low order. 
Like them 
also they consist only of two simple round auditive capsules whose transparent, 
solid walls contain sometimes a single, sometimes several otolites, suspended 
in a clear liquid, and which are composed of carbonate of lime.” 
4 With the Pectinibranchia, there are usually 
two conical tentacles ; more rarely are there four 
as with Amphorina, Eolidina, Flabellina, and 
Aeolis, Cutaneous furrow-like prolongations are 
observed with Notarchus, Dolabella, Pleuro- 
branchus, Pleurobranchaea, and Aplysia. With 
Doris, Tritonia, and Scyllaea, the two conical 
tentacles can be withdrawn into particular tubular 
excavations of the mantle.* 
5 Flabellina, Aeolis, Doris, Phyllidia, Dori- 
dium, Aplysia, Pleurobranchus, Pleurobran- 
chaea, Dolabella, Ampullaria, Ceratodes. These 
cutaneous lobes are often so large, that one is dis- 
posed to include them among the real tentacles. 
6 I refer here to the tentacle-like organs by which 
Clio, Pneumodermon, and Spongiobranchaea 
fix themselves upon marine bodies (§ 204), to the 
filaments of the anterior lobes of the mantle of 
Thetis, Plocamophorus, and T'ritonia thetidea, 
and to the prolongations of the lateral border of the 
same organ with Haliotis, Doris fimbriata, and 
Cypraea erosa. 
1 Eudougz and Souleyet (Institut. 1838, No. 
255, p. 376, or Froriep’s neue Not. No. 174, 
1838, p. 312,) were the first to notice the auditive 
organ with the Cephalophora. They found with 
Pterotrachea, Carinaria, Pneumodermon, and 
Phyllirrhoé, as also Gaudichaud with Atlanta, 
that the auditive capsules are small round semi- 
t parent bodies attached by a ped upon 
the cerebral mass. Laurent (Append. aux re- 
cherch. sur les organes auditifs des Mollusques, in 
the Ann. franc. et étrang. d’Anat. et de Physiol. 
Mai, 1839, p. 118, fig. 1-16) has described these 
organs with their crystalline contents a little more 
fully, for, beside the figures of Eudouw and Sou- 
leyet relative to Hyalea, Cleodora, and Creseis, 
he has added others concerning Limaz and Helix. 
Since then these organs with their otolites of differ- 
ent Heteropoda, Pteropoda, and Gasteropoda have 
been described in detail by Krohn (Miller’s Arch. 
1839, p. 335, or Froriep’s neue Not. XIV. 1840, 
p. 810, XVIII. 1841, p. 310). In another series 
of the terrestrial and fresh-water Gasteropoda, I 
*{§210, note 4.) Hancock and Embleton 
(oe. cit.) regard these tentacles as olfactory organs, 
a view which is sustained by their special anato- 
my, by their special and comparative relations. 
Moquin-Tandon also (Bibl. Univer de Genéve. 
Nov. 1851, p. 247) regards this sense as located in 
the end of the tentacles, with the Gasteropoda 
When 
have attempted to show the analogy of these organs 
with the auditive organs of the embryos of fishes 
(Wiegmann’s Arch. 1841, I. p. 148, Taf. IV. or 
Ann. d. Sc. Nat. XIX. 1843, p. 193, Pl. II. B.). 
Kélliker (Ueber das Gehirorgan der Mollusken, 
in Froriep’s neue Not. XXV. 1843, p. 133) also 
has described them with many marine Heteropoda, 
and Gasteropoda, so that they may be said to exist 
in all the Cephalophora which have been subjected 
to dissection. The following are the genera in 
which they have been observed. Among the Pter= 
opoda: Cymbulia, Tiedemannia, Hyalea, Cre- 
seis, Pneumodermon, Limacina ; Heteropoda : 
Carinaria, Pterotrachea, Phyllirrhoé, Atlanta; 
Gasteropoda: Rhadope, Flabellina, Li: > 
Amphorina, Pelta, Chalidis, Zephyrina, Actae- 
on, Actaeonia, Aeolis, Venilia, Tergipes, Do~ 
ris, Polycera, Tritonia, Thetis, Diphyllidia, 
Ancylus, Doridium, Aplysia, Gasteropteron, 
Umbrella, Notarchus, Pleurovranchus, Pleuro- 
branchaea, Paludina, Lymnaeus, Planorbis, 
Physa, Bulimus, Clausilia, Succinea, Heliz, 
Arion, and Limazr. It is remarkable that the 
auditive organs are developed so early, for they 
may be distinguished while the embryo is still in 
the egg. From the account of Pouchet (Ann. d. 
Sc. Nat. X. 1838, p. 64), it appears that he saw the 
otolites in motion in an embryo of a Lymnaeus, 
but without knowing their nature. Loven also, 
who saw the two capsules in the young Eolis 
(Kongl. Vetensk. Acad. Handl. 1839, p. 227, or 
Isis, 1842, p. 860, Taf. I. fig. 1, 0.) did not know 
what to think ofthem. Van Beneden (An. a. Se. 
Nat. XV. 1841, p. 127, Pl. I. fig. 18, 15, 17, d.) 
mistook them in the embryos of Limaaz and Aply- 
sia, for nervous ganglia; while A//man (loc. cit. 
p. 153, Pl. VII. fig. 10-12, d.) regarded them as 
eyes in the embryos of Actueon. Sars (Wieg- 
mann’s Arch. 1845, I. p. 8, Taf. I. fig. 7-11) and 
Nordmann (loc. cit. p. 44, 87, Taf. IV. V.),on the 
other hand, very correctly recognized them as or~ 
gans of hearing in the embryos of Doris, Trito- 
nia, Tergipes, Buccinum, Littorina, Cerithium, 
See also Hancock (Ann. Nat. Hist. 1852, IX. p. 
188) on this apparatus with the Bullidae. In these, 
no proper tentacles exist, as is well known, but this 
author shows that here the head-lobe, which is the 
result of the fusion of tentacles, is the seat o° this 
sense, — Ep, 
