210 THE CAUSES WHICH PROPAGATE 



open to doubt, there yet remains somewhat to be desired, as all 

 experimenters take for granted the sounds emitted by insects 

 in flig'ht are simply due to the wings beating the air at an 

 almost incredible speed ; and to prove this, the would-be measurer 

 of movement or sound fixes his subject on a pin, when the 

 limber-vans, urged and vexed by impatience at captivity, make 

 unwonted exertions, and thus cease to manifest their impertur- 

 bable momentum of flight. Then, in the two cases where 

 sound is to be measured, we have to trust to the fineness of the 

 operator's ear, who compares mentally his buzzing insect with 

 the whirr of the cardboard or sing of the syren. On the other 

 hand, in measuring the wing-beats, the blackened cylinder must 

 chiefly fail, from a difficulty in the adjustment of mechanism to 

 the nervous motions of an animated object. 



Turning to the physiological character of these sounds, we 

 find the males of various birds produce on the wing a strange 

 winnowing or atmospheric concussion, arising from a modification 

 in the form of certain of their wing or tail feathers, which are 

 pointed or clubbed, and during the pairing-time are thus . 

 rendered subservient to the emotions in the production of these 

 singular calls. An example of this kind of music is afforded 

 us by the male of the common Snipe, Avhieh now and again 

 startles the wanderer in the fenland by a sudden and rapid fall 

 from the zenith, accompanied with a mysterious drumming."^ 

 But in respect to insects — although among the aerial butterfly 

 and moth kind some are observed to possess various and fan- 

 tastic wing outline — I am aware of no instance in which musical 

 modulations have been ascertained to arise from this peculiarity. 

 On the contrary, it is remarkable that bees and flies which 

 have the precedence as hummers and buzzers have uniformly 

 triangular wings, and that they give out their varied and 

 various sounds rather in proportion to the size or content of 

 their body than in the ratio of their wing area. A remarkable 

 phenomenon likewise presides over this music — namely, it 

 is subject to atmospheric perturbations. Gnats, species so 

 sonorous and vindictive during summer heats, Avhen the damp 



* Various instances of this music are given in "The Descent of Man." 

 Distinct from laryngeal voice, it seems to correspond to the instrumental music 

 i)f Insecta. 



