1889. 



THE YOUNG NATURALIST. 



195 



in the shape of the poisers, and I have frequently observed them to 

 beat rapidly on the alulae during buzzing, thereby undoubtly helping 

 to swell the volume of sound. A substantial proof of this is afforded 

 by the following simple experiment. Take a sheet of paper and bend 

 it double without absolutely folding it flat, in the likeness of a letter U> 

 thus forming a sufficiently accurate model of one of the alulae. 

 Against it place a tuning fork, which will do duty for a poiser. Now 

 if the latter be beaten against the paper — otherwise the winglet — no 

 buzz is produced, simply because the vibratory blows are not repeated 

 with the necessary rapidity to reach the ear in one continuous sound. 

 But by striking the fork, thereby obtaining a rapid to and fro move- 

 ment of the prongs, exactly answering to the vibration of the halteres, 

 and permitting the same to come into bare contact with the paper, an 

 excellent imitation of the buzz of an angry fly is the result. 



But the winglets are not found in all Diptem, and some other 

 reasons must be found to account for the persistence of the sound in 

 such species. The halteres nevertheless remain, and somewhat 

 counterbalance the deficiency by their additional length, though it 

 should be remembered that the noisiest diptera are those provided 

 with alulae. Dr. Burmeister discovered that the buzz of a species of 

 Eristalis was continued even after the alulae, the halters, and all but 

 the stumps of the wings were removed, but he remarks that the sound 

 was decidedly weaker and higher pitched. A contiuance of his 

 researches showed him that the spiracles lying between the meso-and- 

 meta-thoraces, at the base of the halteres were also productive of 

 sound, caused by the forcible expulsion of a stream of air through the 

 same. But in this direction I cannot pursue the subject further, it 

 being the province of the present paper to deal only with the wings of 

 insects — I mention the fact for the sake of completeness. 



I had before occasion to remark that the buzz of a fly ceases when 

 it settles. The reason is sufficiently obvious without my referring to 

 it, beyond remarking that the wings are then laid at rest, and 

 accompanying the repose of those organs is the cessation of the 

 vibratory movement of the poisers. This I have found to be invari- 

 ably the case, unless the wings move the halteres remain stationary ; 

 hence the absence of sound when the former are held extended, as 

 before explained. 



Observers disagree upon the actual origin of the buzzing of flies, 

 and as there is no reason to suspect that any particular one is correct, 

 and that all others are under erroneous ideas, it appears to me more 

 justifiable to argue that the aggregate or sum of all these causes, com- 



