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



fibril. On extending this line I found that it always cut within 

 5° of the position of the source of the sound. The antennae of 

 the male mosquito have a range of motion in a horizontal di- 

 rection, so that the angle included between them can vary con- 

 siderably inside and outside of 40°*; andlconceive that this is 

 the manner in which these insects during night direct their 

 flight toward the female. The song of the female vibrates the 

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

 other. The insect spreads the angle between his antennae, and 

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

 angle formed by the antennae, 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 5° 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 earf. 



* The shafts of the antennae include an angle of about 40°. The basal 

 fibrils of the antennae form an angle of about 90°, and the terminal fibrils 

 an angle of about 30°, with the axis of the insect. 



t Some physiologists, attempting to explain the function of the semi- 

 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 



