324 



THE CRUSTACEA. 



S^ 2TG. 



nally, those organs are lined by a soft membrane, which contains a nerve 

 arisinnf from the brain in common with the internal antennal nerve. '■^^ 



o 



§ 276. 



Organs of Hearing, with the Crustacea, have as yet been observed only 

 with the Decapoda."* With these Crustacea, there is a hollow conical pro- 

 cess, perforated at its obtuse apex, on the lower surface of the basal joint of 

 the external antennae. Its opening is always closed by a kind of Tympa- 

 nitic membrane, in tlie centre of which there is usually a fissure.^-* Behind 

 this conical process, and in the cephalothorax, there is a large, thin-walled 

 sac, filled with a clear li((uid ; this is prolonged by a kind of neck into the 

 process, and has, undoubtedly, the function of a Labyrinthus,^^^ for, a 

 special nerve, arising from the lateral parts of the brain, in common with 

 the external antennal nerve, is spread upon its walls. ^'" 



The base of this labyrinth is in connection with a singular glandular 

 organ, of a usually greenish color, but whose nature is yet undetermined.'^' 



1 These olfactory organs were first described and 

 considered as such by Rosenthal {liciPs Arch. X. 

 1811, p. 433, Taf. VIII. fig. 1-4) with tlie craw-fish 

 and lobster. Treviranus (Biologie, VI. 1822, p. 

 308) has subsequently confirmed these observations 

 with the lobster. See, for this same animal, Milne 

 Edwards, Hist. Nat. d. Crust. PI. XII. fig. 1. 

 These organs have been found latterly, also, by 

 Farre, with Palinurus and Pa^urus, (I'hilos. 

 Trans. 1843, p. 233, PI. IX. X. and Ann. of Nat. 

 Hist. XII. p. 229). I have myself observed them 

 with Palaemon, Nephrops, and Mala. It is diffi- 

 cult to understand how Farre could have taken 

 these cavities for organs of hearing into which 

 grains of sand, entering by accident, would serve 

 as otolites. 



1 Although special auditive organs have not yet 

 been observed with the other Crustacea, yet it 

 cannot be denied that they are sensible to sounds. 

 At least, the observations of Coldstream (Cyclop. 

 of Anat. I. p. OSS) show that the Cirripedia have 

 a very acute sense of hearing, for they appear 

 cognizant of the slightest sound, and quickly close 

 the shell. 



'i This cylindrical protuberance, with its tym- 

 panitic meraljrane, is easily seen in the basilar ar- 

 ticle mentioned, with Homarus, Astacus, Ne- 

 phrops, Palinurus, and other Macrura ; — see 

 Scarpa, Anatom. disquis. de auditu et olfactu. 

 p. 2, Tab. IV. fig. 4, a. b. ; fVeber, he aure animal, 

 aquatil. p. 8, 106, Tab. I. fig. 1, No. 1, and Milne 

 Edwards, Hist. Nat. d. Crust. PI. XII. fig. 11, o, 

 {Astacus). This protuberance is long and cylin- 

 drical with Pagurus striatus, and Hoinola Cu- 

 vieri. 



With the Slaiina, whose antennal articles are 

 large and immovable, the auditive organs are 

 slightly protuljerant, and situated near the mouth. 

 See Savigny, Descrip. de I'Egypte, loc. cit. PI. 

 A'l. fig. 4.J and tj.-- a. e. {Mala and Stenorhyn- 

 chus), and Milne Edwards, loc. cit. I. p. 268. PI. 

 III. tig. 2, e. PI. XV. fig. 2, 10, 16 {Maia, Mith- 

 rax, Leucippa, and Camposcia). 



With Sci/llarus latus, whose antennae are very 

 large and fi.xed at their base, the large but flat 

 auditive cylinders are very short and near together 

 on the biirders of the mouth (Savigny loc, cit. PI. 

 VIII. tig. l.n. a. e.). With 'icyllarus arctus, I 



* [^ 27G, note 2.] The organ of hearing in Leu- 

 cifer first noticed by Souleyet, has since been 

 studied by Huxley (Ann. of Nat. Hist. 1851, p. 

 304) who appears to have clearly made out the 

 sti'ucture which resembles the ordinary form of 



have found the same concealed in the semilunar de- 

 pressions which are underneath the mouth. With 

 Maia, these cylinders are obJiijuely truncated, and 

 are articulated with the large and basUar articles 

 of the antenna;. They can be depressed towards 

 the inner side, and then righted as a kind of ex- 

 ternal auditive conch, and for this pui-pose the in- 

 ternal surface of the cylinder has a pair of mus- 

 cles which are inserted on an internal, stirrup-like 

 process ; see Cavolini, Abhandl. iiber die Erzeu- 

 gung d. Fische und der Krebse, p. 133, and Milne 

 Edwards, Hist. Nat. d. Crust. I. p. 124, PI. XII. 

 fig. 10, e. 1. m., and fig. 11, or in Cyclop, of Anat. loc. 

 cit. p.768, fig. 397, 398. Further researches are nec- 

 essary, before the opinion of Souleyet (Froriep^n 

 neue Notiz. XXVIII. p. 84) can be admitted, that 

 a small, round, glittering body which, with Leucifer, 

 is situated at the base of the internal antennae, is 

 an auditive organ.* 



3 Formerly, the attention had been called only to 

 the portion of this labyrinth which is concealed in 

 the auditive cylinder {Scarpa, loc. cit. Tab. IV. 

 fig. 6, and IVeber, loc. cit. Tab. I. fig. 2). It is 

 only lately that it has been shown that this small 

 auditive vesicle belongs to a very large ampulla sit- 

 uated at its base ; see Brandt, Mediz. Zool. II. p. 

 64, Taf. XI. tig. 13, a. a., and Neuwyler, Anatom. 

 Uutersuch. iiber den Flusskrebs, in the Verhandl. 

 d. scliweizer. Naturf. Gesellsch. bei ihrer Versam- 

 mel. zu Zurich, 1841, p. 176. 



4 Scarpa, loc. cit. Tab. IV. fig. 5, g. g., and fVe- 

 her, loc. cit. Tab. I. fig. 2, No. 7 ; Brandt, and 

 Neuwyler, loc. cit.; Farre, Philos. Trans. 1843, 

 PI. IX. fig. 10, e. e. 



5 This glandular body which appears to be pres- 

 ent with the Urachyura also, is situated, with the 

 Astaciua, behind the base of the external antennae, 

 concealed in the lower portion of the shell, and 

 covered, in part, by the membranous labyrinth ; see 

 Roesel, loc. cit. p. 322, Tab. LVIII. fig. 9, c; 

 Sue/cow, loc. cit. p. 55, Taf. IX. fig. 2, a.; Brandt 

 Mediz. Zool. p. 64, Taf. XI. fig. 8, k. (Astacus), 

 Milne Edwards, Hist. Nat. d. Crust. PI. XII. 

 fig. 9, a. 10, g. (Astacus and Maia). Neuwyler 

 has given the green glands of the craw-fish a spe- 

 cial examination (loc. cit.). He found that they 

 consisted of an intestinoid tube communicating 

 with the membranous labyrinth. At first he 



auditory apparatus in the MoUusca. See also 

 Schodler (H'iegmann^s Arch. 1846, p. 363) upon 

 this organ with Acanthocercus rigidus ; finally, 

 Darwin, loc. cit. Cirripedia, p. 53. — Ed. 



