399 
FISHES 
CHAP. 
The physiological raison détre of the connexion between the 
air-bladder and the auditory organ cannot yet be regarded as 
satisfactorily determined. 
Fic, 223.—Diagram to show the Weberian 
ossicles and their relations to the ear 
and the air-bladder. af, Atrium, an 
extension of the sinus impar; 4@.v.¢, 
anterior vertical canal ; b.w, bony wall of 
the periotic capsule ; d.e, the medianly- 
united endolymphatic ducts ; h.c, hori- 
zontal canal ; 7”, intercalarium, a third 
ossicle imbedded in the ligament (7./g) 
connecting the scaphium with the 
tripus ; ”, 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.z7, sinus impar; ¢7.a, ¢r.c. the 
anterior and crescentic parts of the 
tripus ; wt, utriculus. The radial lines 
represent the fibres of the dorsal wall of 
the air-bladder. (From Bridge and 
Haddon.) 
that the Weberian mechanism is 
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." 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 
be presumed, are naturally 
brought about by the varia- 
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 
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 
1 See also Sérensen, Journ. Anat. and Phys. xxix. 1895, p. 399; and Bridge, 
Journ. Linn. Soc. xxvii. 1900, p. 531. 
° Bridge and Haddon, op. cit. p. 261. 
3 Id. Proc. Roy. Soc. lii. 1892, p. 189. 
