Ainlitiirij ^[j)j)aiatus of llir (Julcx liios(iuiti). Jjol 



Althoiigii llic liumological (■oinitxions existing; between the 

 vertebrates and articulates, even when advocated by naturalists, 

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

 j)ose 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 j)art 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 

 lest, 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 

 1 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 

 with the physical conditions necessary for them to receive and 

 transmit vibrations to the interior ganglia. 



Naturalists, in their surmises as to the positions and forms of 

 the organ of hearing in insects, have rarely kept in view the im- 

 portant consideration of those physical relations which the 

 organ must bear to the aerial vibrations producing sound, and 

 which we have already pointed out. The mere descriptive ana- 

 tomist of former years could be satisfied with his artistic faculty 

 for the perception of form ; but the student of these days can 

 only make progress by constantly studying the close relations 

 which necessarily exist between the minute structure of the 

 organs of an animal and the forces which are acting in the 

 animal, and which traverse the medium in which the animal 



