AIE-BLADDEE IN NOIOPTEEUS BORNEES-SIS. 537 



to do with a simpler physiological role ? The danger which a 

 Fish incurs from over-distension of the air-bladder as the result 

 of a too rapid, rise in the water to the reduced pressure of a 

 higher level has been emphasized elsewhere (2) ; and, without 

 involving any alteration in the rate of gaseous absorption, the 

 afferent impulses communicated to the auditory organ may, 

 through appropriate efferent channels, lead to such modifications 

 of the locomotor movements as will enable the Pish to guard 

 against over-distension, and return to its normal plane of 

 equilibrium or " least effort " at a greater depth. 



It is a significant illustration of the difficulties of the problem 

 that even Weber, who was primarily responsible for the theory 

 of the auditory function of the air-bladder in those Rshes in 

 which that organ is connected with the membranous labyrinth, 

 was sufficiently far-seeing to admit the possibility of a second 

 function. Immediately following the quotation with reference 

 to Sparus, which has been previously given, Weber proceeds 

 (12. pp. 72-73) :— 



" Altera vesicae natatorise utilitas haec est, ut acre vesicae com- 

 pressione alvi in appendices superiores impulso, membranaque 

 feuestram utramque vestibuli ossei obducente tensa et introrsum 

 pressa, aqua cranii cavum replens adeoque vestibulum membra- 

 uaceum, ad hac aqua circumdatum ipsum prematus. 



" Quam ob rem, si cranio aperto et labyrintho rnembranaceo 

 conspicuo vesica natatoria manu comprimatur, facile hie vesicae 

 natatorise contractse effectus oculis percipitur. Per vesicam enim 

 manu compressam liquor cranium replens non solum propellitur, 

 sed vestibulum membranaceum ipsum quoque motu liquoris 

 cranii commovetur." 



The two paragraphs just quoted suggest that Weber certainly 

 entertained the idea of the air-bladder being the means of con- 

 veying to the auditory organ stimuli due to its varying degrees 

 of distension, such as, we may presume, are naturally brought 

 about by variations of depth and, therefore, of pressure ; and,, 

 further, prompt the remark that the term " Weberian theory " 

 may be as reasonably applied to this view as to the " auditory 

 theory " with which the name is more generally associated. 



In conclusion, it may be affirmed that there are obvious objec- 

 tions both to the auditory and hydrostatic views of the physio- 

 logical raison d'etre of the connection between the air-bladder 

 and the auditory orgnns, which, in the present state of our 

 knowledge of the individual functions of those organs, cannot 



