376 COMPARATIVE ANATOMY OF THE EAR. 



we can not tell why. In the case before us, we therefore can expect no 

 assistance in the way of arguments from mechanical philosophy, and are 

 limited to the use of those which may "be drawn from comparative anat- 

 omy and physiology. 



Examining, therefore, what appears to be the primitive plan of the con- 

 Illustration of struction of this mechanism, we find it to consist of a nerve 

 thisexpiana- fibril .in connection with an otolith, or little stony body. 



tion from com- ^ . j i i i i r 



parative anat- Such a construction, included in a bag 01 water, constitutes, 

 m y- in point of fact, the organ of "hearing of some of the lower 



tribes, as the gasteropodous molluscs. These animals can have no per- 

 ception of the pitch of sounds or musical notes, and only an imperfect one 

 of intensities. But what they do distinguish is one noise from another. 

 Now the idea conveyed to the mind by difference of noises is precisely 

 the distinction that we are dwelling on, that of quality. 



If, instead of restricting our examination to the semicircular canals, we 

 General view exten( ^ & * tne whole organ of hearing, and consider to- 

 of the auditory gether, in the case of each animal tribe, its requirements, and 

 sm ' the manner in which those requirements are satisfied, we 

 shall meet with a surprising confirmation of the preceding views. The 

 lowest requirement we can conceive of is the appreciating of noises ; an 

 advance upon this is the determination of their direction ; a higher ad- 

 vance, the determination of their intensity ; and a still higher, the rec- 

 ognition of those combinations of impulses which constitute a musical 

 sound. For each of these successive requirements the auditory mech- 

 anism must necessarily become more complex ; and thus it first ap- 

 pears, as we have just stated, as a sac of water, containing a stony grain 

 or otolith imbedded in the cesophageal collar. A noise agitates the oto- 

 Com arative ^^' an< ^ ^7 i ts movement the perception of a sound ensues, 

 anatomy of the In cephalopodous molluscs the auditory sac is detached, and 

 the intercommunicating thread represents the rudiment of 

 what, in the higher grade of development, will be the auditory nerve. 

 With another advance the sac is lodged in a cartilaginous cavity. Thus, 

 in the cuttle-fish, a simple cartilaginous vestibule exists, having within 

 it a membranous bag or auditory capsule, filled with fluid, and upon the 

 capsule the filaments of the auditory nerve are spread. An otolith or 

 ear-stone is placed within, and this constitutes the entire apparatus, while 

 yet there is no vibrating membrane and no fenestral aperture. 



Even in still higher conditions the purely mechanical character of the 

 structure is manifest, and so, in some of those in which the sac opens ex- 

 teriorly, grains of sand, that have been introduced by chance from without, 

 rest on the hair like filaments which the auditory sac contains, each fila- 

 ment apparently including a nerve fibril. In a still higher condition of 

 advance, as, for example, in the lobster, a portion of the shelly wall which 



