INSECT VARIETY. 211 



of autumn comes on may not unfrequently be observed flying 

 about our apartments quite noiselessly ; but I will not pretend 

 to decide whether this may be owing- directly to the weather, or 

 whether it proceeds indirectly from its chilling influence on the 

 slender palpitating frame. 



That these aerial notes of various colour do not take origin 

 in flight may be easily shown in these orders ; for if we capture 

 a fly or bee traversing our apartment with loud sound, we notice, 

 although the deep resonance of locomotion has ceased, it con- 

 tinues its song when retained in the hand. And if we then 

 begin and methodically clip the wings from the tip down to 

 their roots, it will become further evident that, although the 

 sound during this operation has risen in pitch, its emission con- 

 tinues in greater or less intensity as long as the thoracic muscles 

 remain in action. We have thus a fundamental music inde- 

 pendent of wing-motion to account for, and that this arises 

 from increased respiration, induced by muscular action at the 

 tracheal spiracles, has been more or less satisfactorily shown by 

 Chabrier and Burmeister in the case of flies, and by John 

 Hunter as regards bees. 



Chabrier informs us that in the Bluebottle the hinder 

 thoracic spiracles (metathoracic) ai-e closed by (two) little scaly 

 lips, and if these be carefully removed with a fine needle the 

 buzz of the insect is scarcely audible during flight. Bur- 

 meister advanced further. Having removed all movable ex- 

 ternal parts from the common Drone Fly of our flower-beds, 

 which still continued its peculiar notes, he also became convinced 

 the sound arose at these same metathoracic spiracles, which 

 he proceeded to dissect. He then discovered their edges to be 

 furnished internally with a fringe of parallel membranous plates, 

 horizontally overlapping and decreasing in size towards either 

 extremity. In this insect there are fifteen such on either edge 

 (See Plate V., Fig. 6, /) . Dr. Landois follows Burmeister. By 

 cutting the thorax in two longitudinally, and removing the 

 longitudinal and oblique wing-muscles so as to expose the mouth 

 of a posterior spiracle, we may with aid of magnifying power 

 discover these serrated laminae, comparable to a curry-comb or 

 Pan^s-pipe, present in a majority of flies. In the Hover Flies, 

 where they are most conspicuous, their position and appearance 

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