238 



THE CEPHALOPIIORA. 



§ 211. 



simple this otolitc is spherical and crystalline, but when multiple they are 

 fusiform, a little conj|)resscd, and usually very numerous, there being with 

 gome Gasteropoda, thirty or forty, and even eighty iu each capsule.'-' 



The movements of those 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 those 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 

 oesophageal ring. In only a very few of the genera are the two auditory 

 nerves separated and distinct from each other.'"' 



Phasianella, and Rissoa. I have myself seen 

 them quite early in the embryos of Vermetus .* 



2 Thei'e is a single otolite only with the Hetero- 

 poda, the Tubulibranchia and several of the Ap- 

 neusta ; S3e Delte Cliiaje, Descriz. &c. II. p. 100, 

 Tav. L.VIII. fig. 5, 6 (Carinaria), and Qiiatre- 

 fages, Ann. d. Sc. Nat. 1. 1841, p. 160, PI. VI. fig. 

 8-10 {Actaeoii, Pelta, Chalidifi). According to 

 Krohn^s auil my own observations, there are 

 groups of small fusiform otolites with some Ptero- 

 poda, and very many of the Gasteropoda, as Cym- 

 bulia, Hi/u/ea, Doris, Tritonia, Thetin, AerUis, 

 yenilia, Pleurobranchaea, Paludina, PlannrOif:, 

 Lymnaens, Helix, Liinax, and many others. It 

 is not rare to ti,nd among these fusiform otolites, 

 others composed of two or four calcareous corpus- 

 cles. Those of a spherical or spindle shaije divide, 

 from pressure, into four to eight fragments in the 

 direction ol cruciform lines which may often be seen 

 before division. According to the observations of 

 Laurent, Krolin, and mys.df, 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 Freij, in 

 Frorie/j's neue Not. XXXVII. No. 801, p. 132, 

 and iriegmann''s Arch. 1845, I. p. 217. Taf. IX.f 



3 A priori, it might have been inferred that these 

 motions are due to cilia, for the otolites never come 

 in contact with the sides of the capsule, but al- 



* [ § 211, note 1.] See also Alder and Hancock 

 loc. cit. Part 11. PI. II. fig. 11 (Dendronotus), PI. 

 IV. fig. 18 (Doto); Part. III. PI. VIII. fig. 4, 5, 

 6 (Aeolis); Part V. PI. II. fig. 15 (^Doris) ; then 

 Leydii^, Uebcr Paludina vivipara, &c., loc. cit. p. 

 139, 155, Taf. XI. fig. 12, k. Taf. XIII. fig. 14-24, 

 49, II. {Paludina) ; and Leidy, loc. cit. p. 246, PI. 

 IX. fig. VII.-IX. {Helix), PI. 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, rt 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. — Ed. 



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. fVagner 

 (Lehrbuch der Physiol, ed. H. 1843, p. 463) positive- 

 ly attirms that he has seen cilia in these capsules. 

 They have been very distinctly seen by Kijlliker 

 also (loc. cit.) with Tritonia, Thetis, PLeuro- 

 branchaea, Diphyllidia, Hyalea, Lissosoma, and 

 Rhodope. 



i See Laurent, loc. cit. fig. 1-6, ant Quatre- 

 fages, Ann. d. Sc. Nat. I. loc. cit. PI. IV. VI. Ac- 

 cording to Delle Ckiaje (Descriz. &c. loc. cit. Tav. 

 liXIII. fig. 3, d. 14, f.), and Milne Edwards 

 (Ann. d. Sc. Nat. XVIII. 1842, PI. .XI. fig. 1, z. 

 fig. 3, h.), the auditive nerves are very long with 

 Carinaria. AVith many Ccphaloi>hora which are 

 trans])arent, the auditive organs may be perceived 

 by the naked eye, through the skin, as two white 

 spots. }■ 



3 Doris, Thetis, Tritonia, Aeolis {Krohn, Inc. 

 cit.), and Tergipes {Nordmami, loc. cit. p. 44, 

 Tab. II.). 



li According to Krohn (loc. cit. No. 394, p. 311) 

 the two auditive capsules of P/eurobranchaea, a.t\d 

 Paludina receive distinct auditive nerves from the 

 inferior portion of the oesophageal ring. He has 

 observed the same with Cymbulia, and Hyalea 

 (loc. cit. No. 306, p. 311) i but Van Beneden (E.\- 



t [ § 211, note 2.] See, for the auditory appara- 

 tus of Aeolis, Hancock and Emb/eton, 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. — En. 



j L§ 211, note 4.] See also Leydig (Anat. Be- 

 merk. iib. Carinaria, Firola und Aniphicora, in 

 Siebold and Kiilliker'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 

 cai)sules 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. XIII. 

 1845, p. 43. — Ed. 



