Audiionj Appdratn.s of the (Jiilex mosquito. 859 



fibrilhe of one of the antennae more forcibly than those of the 

 other. The insect spreads the angle between his antenn;e, and 

 thus, as I have observed, brings the fibriilfc, situate within the 

 angle formed by the antenna', in a direction approximately pa- 

 rallel to the axis of the body. The mosquito now turns his 

 body in the direction of that antenna whose fibrils are most 

 affected, and thus gives greater intensity to the vibrations of the 

 fibrils of the other antenna. When he has thus brought the vi- 

 brations of the antennae to equality of intensity, he has placed his 

 body in the direction of the radiation of the sound, and he directs 

 his flight accordingly ; and from my experiments it would appear 

 that he can thus guide himself to within S'* of the direction of 

 the female. 



Some may assume (as I did when I began this research), 

 from the fact of the covibration of these fibrils to sounds of dif- 

 ferent pitch, that the mosquito has the power of decomposing the 

 sensation of a composite sound into its simple components, as is 

 done by the higher vertebrates ; but I do not hold this view, 

 but believe that the range of covibration of the fibrils of the mos- 

 quito is to enable it to apprehend the ranging pitch of the 

 sounds of the female. In other words, the want of definite and 

 fixed pitch to the female's song demands for the receiving-appa- 

 ratus of her sounds a corresponding range of covibration ; so 

 that, instead of indicating a high order of auditory development, 

 it is really the lowest, except in its power of determining the di- 

 rection of a sonorous centre, in which respect it surpasses by far 

 our own ear*. 



The auditory apparatus we have just described does not in the 

 least confirm Helmholtz's hypothesis of the functions of the 

 organ of Corti ; for the supposed power of that organ to decom- 

 pose a sonorous sensation depends upon the existence of an audi- 



• Some physiologists, attempting to explain the function of the serai- 

 circular canals, assume, because these canals are in three planes at right 

 angles to each other, that they serve to fix in space a sonorous centre, just 

 as the geometrician by his three coordinate planes determines the position 

 of a point in space. But this assumption is fanciful and entirely devoid of 

 reason ; for the semicircular canals are always in the same dynamic rela- 

 tion to the tympanic membrane which receives the vibration, to be trans- 

 mitted always in one way through the ossicles to the inner ear. Really 

 we determine the direction of a sound by the difference in the intensities 

 of the effects produced in the two ears; and this determination is aided by 

 the form of the outer ear, and by the fact that man can turn his head around 

 a vertical axis. Other mammalia, however, having the axis of rotation of 

 the head more or less horizontal, have the power of facilitating the de- 

 termination of motion by moving the axis of their outer ears into differ- 

 ent directions. It is also a fact that, when one ear is slightly deaf, the 

 person unconsciously so affected always supposes a sound to come from 

 the side on which is his good ear. 



25* 



