^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, aie 

 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.'^* When 



4 With the Pectinibranchia, there are usually 

 two conical tentacles ; more rarely are there four 

 as with Amphorina, Eolidina, F/abellina, and 

 Aeolis. Cutaneous furrow-Uke prolongations are 

 observed with Notarchus, Dolabella, Pleiiro- 

 branchus, Pleurobranchaea, and Aplysia. With 

 Doris, Tritonia, and Sci/Uaea, the two conical 

 tentacles can be withdrawn into particular tubular 

 excavations of the mantle.* 



5 Flabe/lina, Aeolis, Doris, Phyllidia, Dori- 

 dium, Aplysia, Pleurobranchus, Pleurobran- 

 chaea, Dolabella, Ampullaria, Ceratodes. These 

 cutaneous lo))es 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 Sponsiobranchaea 

 fix themselves upon marine botlies (5 204), to the 

 filaments of the anterior lobes of the mantle of 

 Thetis, Plocamophorus, and Tritonia thetidea, 

 and to the prolongations of the lateral border of the 

 same organ with Haliotis, Doris ßmbriata, and 

 Cypraea erosa. 



1 Eiuloux 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 witli the Cephalophora. They found with 

 Pterotrachea, Carinaria, Pneumodermon, and 

 Phyllirrhoi, as also Gaudichaud with Atlanta, 

 that tlie auditive capsules are small round semi- 

 transparent bodies attached by a peduncle upon 

 the cerebi-al mass. Laurent (Append, aux re- 

 cherch. sur les organes auditifs des MoUusques, in 

 the Ann. franc, et etrang. 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 Eudoux and Sou- 

 leyet relative to Hyalea, Cleodora, and Creseis, 

 he has added others concerning Limax and Helix. 

 Since then these organs with their otolites of differ- 

 ent Heteropoda, Pteropoda, and Gasteropoda have 

 been described in detail by Krohn (Muller''s Arch. 



1839, p. 335, or Froriep's neue Not. XIV. 1840, 

 p. 310, XVIII. 1841, p. 310). In another series 

 of the terrestrial and fi-esh-water Gasteropoda, I 



* [ § 210, note 4.] Hancock and Embleton 

 (loc. 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 Geneve. 

 Kov. 1851, p. 247) regards this sense as located in 

 the end of the tentacles, with the Gasteropoda 



have attempted to show the analogy of these organs 

 with the auditive organs of the eniliryos of fishes 

 (^Wiesmann's Arch. 1841, I. p. 148, Taf. IV. or 

 Ann. d. Sc. Nat. XI.X. 1843, p. 193, PI. II. B.). 

 Kolliker (Ueber das Gehörorgan der Mollusken, 

 in Froriep^s neue Not. XXV. 1843, p. 1.33) 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, Phyllirrhoe, Atlanta ^ 

 Gasteropoda : Rhodope, Flabellina, Lissosoma, 

 Amphorina, Pelta, Chalidis, Zephyrina, Actae- 

 on, Actaeonia, Aeolis, Fenilia, Tergijies, Do- 

 ris, Polycera, Tritonia, Thetis, Diphyliidia., 

 Ancylus, Doridium, Aplysia, Gasteropteron, 

 Umbrella, Notarchus, Pleurobranchus, Pleuro- 

 branchaea, Paludina, Lymnaeus, Planorbis, 

 Physa, Bulimus, Clausilia, Succinea, Helix, 

 Arion, and Limax. 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 Poiichet (Ann. d. 

 Sc. Nat. X. 1838, p. 64), it appears that he saw the 

 otolites in motion in an emljryo 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. 360, Taf. I. tig. 1, o.) did not know 

 what to think of them. Van Beiieden (An. d. &c. 

 Nat. XV. 1841, p. 127, PI. I. fig. 13, 15, 17, d.) 

 mistook them in the embryos of Limax and Aply- 

 sia, for nervous ganglia ; while Allman (loc. cit. 

 p. 153, PI. VII. fig. 10-12, d.) regarded them as 

 eyes in the embrvos of Actaeon. Sars {Wieg- 

 mann's Arch. 1845, I. p. 8, Taf. I. fig. 7-11) and 

 Nordmann (loc. cit. p. 44, S7, 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 tliis apparatus with the Bullidae. In these, 

 no proper tentacles e.xist, 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 a' this 

 sense. — Ed. 



