HEARING IN MOSQUITOES 35 



Perhaps the most interesting result of his experiments was the discovery of 

 the fact that the antennal hairs enable the mosquito to determine the direction 

 from which the sound-waves proceed. He experimented with the song of the 

 female and found that the hairs of the male antennae vibrate when the song of 

 the female comes more or less at right angles to them, while those which point 

 to or from the source of sound are not affected. If the song is directly in front 

 of the head it will be most fully received by the antennal hairs. If the song of 

 the female affects one antenna more than the other, the male, by turning until 

 both antennae are equally affected, could thus determine the direction of 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 aji- 

 tennae, and thus, as I have observed, brings the fibrillae, situate within the angle 

 formed by the antennae, in a direction approximately parallel 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 vibrations 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 ex- 

 periments it would appear that he can thus guide himself to within 5° of the 

 direction of the female." 



While Mayer accepted the function of the antennae as auditory, he clearly 



perceived that no comparison could be made with the sense of hearing in the 



higher vertebrates, and expresses his conclusions in these terms : 



" Some may assume from the fact of the co- vibration of these fibrils to sounds 

 of different 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 verte- 

 brates ; but I do not hold this view, but believe that the range of co- vibration of 

 the fibrils of the mosquito is to enable it to apprehend the varying 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 apparatus of her sounds a corre- 

 sponding range of the co-vibration, so that instead of indicating a high order 

 of auditory development it is really the lowest, except in its power of determining 

 the direction of a sonorous centre, in which respect it surpasses by far our own 



ear." 



Our own observations of the habits of mosquitoes lead us to doubt that the 

 antennae, if auditory at all, are so in their primary function. The foregoing 

 hypotheses are founded upon the assumption that the male seeks the female and 

 is attracted by her song. In fact such is not the case. At least in those forms 

 in which the antennae of the male are most highly specialized the males 

 " swarm " and the female seeks the male. In our experience the song of the 

 female does not attract the male. Mayer appears to have come very near the 

 truth when he found that the antennae served for orientation. One of us (Knab) 

 has observed that the males in a swarm always dance facing the breeze or air- 

 current, no matter how slight this may be, and adjust themselves instantly to 

 any shifting of the breeze. Why this is done would be difficult to explain, but 

 that the antennas make this possible is clearly apparent from Mayer's observa- 

 tions. Of course it can not be denied that the antennae are perhaps also, in a 



