390 



FISHES 



The physiological reason cVitre 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 



he- 



p.v.c 



tna 



tr.c n. 



Fig, 223. — Diagram to show the Weberi.m 



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. ■* On the other 

 hand, it may be urged with 

 perhaps greater probability that 

 the connexion exists for the 

 purpose of conveying to the 

 ear stimuli due to the varying 

 degrees of distension of the 

 air-bladder, such as, it may 

 ossicles and their relations to the ear ijg presumed, are naturally 



and the air-bladder. aU Atrium, an ■*- •^ 



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



anterior vertical canal ; 6.hi, bony wall of fi„,,„ „f T,,T^„«r,4-„j-;„ 



the periotic capsule ;rf.e, the medianly- ^^°'']^ °^ hydrOStatlC pressm'e 



united endolymphatic ducts; h.c, hori- wllich a Msll encOUllters in 



zontal canal ; in, Intercalarium, a third .i p -j - 



ossicle imbedded in the ligament (Ug) ^"6 COUrSe ot its aSCent Or 



connecting the scaphium with the descent in the water.^ Whether 



tripus ; n, bony uodnles on the sides of -, -, 



the complex vertebral centrum ; p.v.c, regarded as an aCCeSSOry tO 



posterior vertical canal ; s. saccuius ; hearing. Or as a means of regu- 



sc, scaphium ; s.e, sinus endolymph- i • , ,. . 



aticus; s.i, sinus impar; ilea, ij-.c. the latmg the distonsion of the 



anterior and crescentic parts of the air-bladder, the physiological 

 tripus ; ut, utnculus. The radial lines c jo 



represent the fibres of the dorsal wall of Value of the Connexion must 



Saddou.')""^^"'' '^""^ ^"''^' '"'^ 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.^ 



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 



^ See also Scirensen, Joimi. Anat. and Phys. xxix. 1895, p. 399 ; and Brid 

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

 ^ Bridge and Haddon, op. cil. p. 261. 

 ^ Id. Proc. Roy. Soc. lii. 1892, p. 139. 



