BY INSECTS IN FLYING. 381 



ture of the stigma. Their presence however is not general : in the Ta- 

 banus bovbius they do not appear, but are found in Eristalis teiiax. I 

 have given an engraving of tiie hinder air-hole, magnified forty times, in 

 which it is shown on the inner side. We find an oval band-like claudent 

 muscle or sphincter, to both ends of which other muscular bands are 

 attached: perpendicular to the inner surface of this claudent muscle stand 

 sixteen to eighteen small horny lamellae, which are of the same breadth 

 as the muscle, and connected in the middle by another longitudinal 

 horny band. On the other side, which is directed outwards, the claudent 

 muscle is clothed with skin, upon which are feathery hairs, which cover 

 the entrance of the air-pipe like a sieve and exclude foreign bodies. I 

 am at present inclined to consider these small horny lamellae rather as 

 a mere scaffolding serving to support the claudent muscle, but leave it 

 to naturalists to decide whether, and how far, they contribute to the for- 

 mation of the sound. In either case however this can be but of little 

 consequence, as many insects possess no such plates. 



I have further to combat some objections which have already been 

 publicly urged against the correctness of my theory of the production 

 of the sound. M. Silbermann has given publicity to this in France by 

 a translation of the chapter of my work which treats on this subject in 

 his Revue Entomologique, by which also M. Goureau was led to perform 

 similar experiments. The latter finds* all that I have said perfectly exact, 

 except that the sound is suspended when the stigma is closed, and this 

 is precisely the main point of the question. On the contrary, however, 

 I must maintain that, although a sound may be heard as long as the 

 gum employed to close the stigma is moist, and the air can make its way 

 through it, none is audible when the gum is perfectly dry. The animal 

 indeed dies of suffocation soon after. M. Goureau has not taken this cir- 

 cumstance into consideration, but has even hazarded the opinion that the 

 sound originates through the friction of the edges of those plates which 

 compose the thorax. This can however be the case in those insects only 

 in which we find on the thorax really distinct plates connected by fibres; 

 and as the diptera are not in possession of such, his theory cannot be 

 applied to them. But even in respect to the other orders with skeleton 

 hips his theory is untenable ; first, because the mobility of these hips, 

 on account of their intimate connection, must be very trifling; and se- 

 condly, because the sound is far too strong to be produced by the friction 

 of such minute surfaces. That the feeble sound of the chirping Capri- 

 corn beetle ( Cerambycina), when the body is in a quiet position, is really 

 produced by such friction is well known; but it is also obvious, from the 

 feebleness of this sound, that the loud buzzing of the flying insects, 

 which besides sounds quite differently, cannot arise from such friction. 



• Revue Kuloiiiulogique, by G. Silbermann, Strasb. 1835, vol. iii. p. 107. 

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