Auditory Apparatus of the Culex mosquito. 351 
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- 
celves the aérial 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 inseet, 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-aquatie 
vertebrates have an imner ear formed so as to bring the aérial 
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 aérial 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 44 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 aérial 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 
