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 

 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 VermeUis.* 



2 There is a single otolite only with the Hetero- 

 poda, the Tubulibranchia and several of the Ap- 

 neusta ; see Delle Chiaje, Descriz. &e. II. p. 100, 

 Tav. LXIII. fig. 5, 6 {Carinuria), and Quatre- 

 fuses, Ann. d. Sc. Nat. 1. 1844, p. 160, PI. VI. fig. 

 8-io (Actaeon, Pelta, Chalidis). According to 

 Krohn's and my own observations, there are 

 groups of small fusiform otolites with some Ptero- 

 l>r>da, and very many of the Gasteropoda, as Cym- 

 bulia, Hyalea, Doris, Tritonia, Thetis, Aeolis, 

 f'enitia, Pleurobranchaea, Paiudina, I^lannrl/is, 

 Lymnueus, Helix, Limax, and many others. It 

 is not rare to find among these fusiform otolitK, 

 others composed of two or four calcareous corpus- 

 cles. Tliose 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 rays?lf, 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. 132, 

 and Wiegmann's Arch. 1845, I. p. 217. Taf. IX.t 



3 A priori, it might have Ijeen inferred that these 

 motions are due to cilia, for the otolites never come 

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



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

 loo. cit. Part II. PI. II. fig. 11 (^Dendronotus), PI. 

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

 6 {Aeolis); PartV. PI. II. fig. 15 (Doris); then 

 I:e-jdin, Ueber Paiudina vivii>ara, &c., loc. cit. p. 

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

 49, R. (Paiudina) ; and Leidy, loc. cit. p. 246, PI. 

 IX. fig. VII.-IX. (Helix), PI. XIII. fig. IV. 4 

 (Helicina). Lcydi^ has furnished valuable con- 

 tributions in the development of tliis organ ; in Pa- 

 iudina, it ai>pears, prior to the nervous system 

 with which it is connected, as an almost solid body 

 with a very small, round, central cavity ; with the 

 p'owth of the organ, this cavity increases, and 

 finally the whole becomes a capsular organ in which 

 »re 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. 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 Kölliker 

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

 branchaea, Diphyllidia, Hyalea, Lissosoma, and 

 Rkodope. 



4 See Laurent, loc. cit. fig. 1-6, and Quatre- 

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

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

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

 ;».r.v. -i. Sc Nat. XVIII. 1842, PI. XI. fig. 1, z. 

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



5 Doris, Thetis, Tritonia, Aeohs (Krohn, loc. 

 cit.), and Tergipes (Nordmann, loc. cit. p. 44, 

 Tab. II.). 



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

 the two auditive capsules oi Pleurobranchaea, and 

 Paiudina 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) ; but Fan Beneden (Ex- 



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

 tus oi 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 atfecled by long treatment with 

 acetic acid. — Ep. 



X [ ^ 211, note 4.] See also Leydig (Anat. Be- 

 merk, üb. Carinaria, Firola und Ami)liicora, ia 

 Siebold and Külliker's Zeitsch. III. 1851, p. 326). 

 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. XIII.. 

 1845, p. 43. — Ed. 



