372 Prof. A. M. Mayer's Researches in Acoustics. 



a view is obtained of the organ of Corti, its parts are rarely 

 in situ, and often they have already had their natural structure 

 altered by the acid with which the bone has been saturated to 

 render it soft enough for dissection and for the cutting of sec- 

 tions for the microscope. 



As we descend in the scale of development from the higher 

 vertebrates, we observe the parts of the outer and middle ear 

 disappearing, while at the same time we see the inner ear 

 gradually advancing toward the surface of the head. The 

 external ear, the auditory canal, the tympanic membrane, and 

 with the latter the now useless ossicles, have disappeared in 

 the lower vertebrates, and there remains but a rudimentary 

 labyrinth. 



Although the homological connexions existing between the 

 vertebrates and articulates, even when advocated by naturalists, 

 are certainly admitted to be imperfect, yet we can hardly sup- 

 pose that the organs of hearing in the articulates will remain 

 stationary or retrograde, but rather that the essential parts of 

 their apparatus of audition, and especially that part which re- 

 ceives the aerial vibrations, will be more exposed than in higher 

 organisms. Indeed the very minuteness of the greater part of 

 the articulates would indicate this ; for a tympanic membrane 

 placed in vibratory communication with a modified labyrinth, or 

 even an auditory capsule with an outer flexible covering, would 

 be useless to the greater number of insects, for several reasons. 

 First, such an apparatus, unless occupying a large proportion of 

 the volume of an insect, would not present surface enough for 

 this kind of receptor of vibrations ; and secondly, the minute- 

 ness of such a membrane would render it impossible to covibrate 

 with those sounds which generally occur in nature, and which 

 the insects themselves can produce. Similarly, all non-aquatic 

 vertebrates have an inner ear formed so as to bring the aerial 

 vibrations which strike the tympanic membrane to bear with the 

 greatest effect on the auditory nerve-filaments* ; and the minute- 

 ness of insects also precludes this condition. Finally, the hard 

 test, characteristic of the articulates, sets aside the idea that they 

 receive the aerial vibrations through the covering of their bodies, 

 like fishes, whose bodies are generally not only larger and far 

 more yielding, but are also immersed in water which transmits 

 vibrations with 4J times the velocity of the same pulses in air 

 and with a yet greater increase in intensity. For these reasons 

 I imagine that those articulates which are sensitive to sound and 

 also emit characteristic sounds, will prove to possess receptors of 

 vibrations external to the general surface of their bodies, and 

 that the proportions and situation of these organs will comport 

 * See Section 4 of this paper. 



