390 



FISHES 



CHAP. 



exists for the 

 conveying to the 

 to the varying 



The physiological raison d'etre of the connexion between the 

 air-bladder and the auditory organ cannot yet be regarded as 

 satisfactorily determined. It is possible, as Weber thought, that 



it may be an auxiliary to the 

 function of hearing by trans- 

 mitting to the ear sound-waves 

 impinging on the surface of the 

 body and affecting the gases in 

 the air-bladder. 1 On the other 

 hand, it may be urged with 

 perhaps greater probability that 

 the connexion 

 purpose of 

 ear stimuli due 

 degrees of distension of 'the 



FIG, 223. Diagram to show the Weberian air-bladder, such as, it may 

 ossicles and their relations to the ear ^ presume d, are naturally 

 and the air -bladder, at, Atrium, an * 



extension of the sinus impar ; a.v.c, brought about by the varia- 

 anterior vertical canal ; b.w, bony wall of 

 the periotic capsule ; d.e, the medianly- 

 united endolymphatic ducts ; h.c, hori- 

 zontal canal ; in, intercalarium, a third 

 ossicle imbedded in the ligament (i.lg) 

 connecting the scaphium with the 

 tripus ; n, bony nodules on the sides of 

 the complex vertebral centrum ; p.v.c, 

 posterior vertical canal ; s. sacculus ; 

 sc, scaphium ; s.e, sinus endolymph- 

 aticus ; s.i, sinus impar ; tr.a, tr.c. the 

 anterior and crescentic parts of the 

 tripus ; ut, utriculus. The radial lines 

 represent the fibres of the dorsal wall of 

 the air-bladder. (From Bridge 

 Haddon.) 



and 



tions of hydrostatic pressure 

 which a Fish encounters in 

 the course of its ascent or 

 descent in the water. 2 Whether 

 regarded as an accessory to 

 hearing, or as a means of regu- 

 lating the distension of the 

 air-bladder, the physiological 

 value of the connexion must 

 be considerable, and on this 

 point it is at least significant 

 that the Weberian mechanism is characteristic of the dominant 

 families of freshwater Teleosts at the present day. 3 



The Olfactory Organs. These organs are essentially a pair 

 of pit-like inpushings of the skin of the ventral side of the head 

 in front of the mouth, with their lining epidermis differentiated 

 into sensory cells separated by supporting cells, and connected 

 with the olfactory lobes of the brain by olfactory nerves. The 



1 See also Sbrensen, Journ. Anat. and Phys. xxix. 1895, p. 399 ; and Bridge, 

 Journ. Linn. Soc. xxvii. 1900, p. 531. 



2 Bridge and Haddon, op. cit. p. 261. 



3 Id. Proe. Boy. Soc. Hi. 1892, p. 139. 



