578 AUDITORY APPARATUS OF THE MOSQUITO. 
nation of the theorem of Ohm, and furnished “a leading thread’ 
which conducted Helmholtz to the discoveries contained in his rè- 
nowned work, “ Die Lehre von den Tonempfindungen.”* In this 
book he first gave the true explanation of timbre, and revealed te 
hidden cause of musical harmony, which, since the days of Pythsg 
oras, had remained a mystery to musicians and a problem to phil 
osophers. 
It may, perhaps, never be possible to bring Helmholtz’s by- 
pothesis of the mode of audition in thẹ higher vertebrates to the 
test of direct observation, from the apparent hopelessness of ever 
being able to experiment on the functions of the parts of the inner 
ear of mammalia. The cochlea, tunnelled in the hard temporal 
bone, is necessarily difficult to dissect, and even when 4 view $ 
obtained of the organ of Corti, its parts are rarely in situ; and, 
moreover, they generally have had their natural structure : 
by the acid with which the bone has been saturated to render it 
soft enough for dissection and for the cutting of sections 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 dis 
appearing, while at the same time we see the inner ear w 
advancing toward the surface of the head. The external eat; W 
auditory canal, the tympanic membrane, and with the o 
now useless ossicles, have disappeared in the lower vertebra ; 
and there remains but a rudimentary labyrinth. i: we 
Althongh the homological connections existing between | i 
tebrates and articulates, even when advocated by naturale 
certainly admitted to be imperfect, yet we can hardly suppos? á 
the organs of bearing in the articulates will remain enpi: 
retrograde, but rather that the essential parts of thet . aerial 
of audition, and especially that part which receives = In- 
vibrations, will be more exposed than in higher ge 
deed, the very minuteness of the greater part of the vibratory 
would indicate this, for a tympanic membrane placed 1’ eap 
communication with a modified labyrinth, or even an moa 
sule with an outer flexible covering, would be useless to the g" 
number of insects for several reasons; first, such an * peor 
unless occupying a large proportion of the volume of $8 
ae = ane orgs! 
aa to Waldeyer, there are 6,500 inner and 4,500 outer Ge , 
