\m.] 225 



Acherontia Atropos. Here there is no oi*gan provided with spiues or 

 teeth, by the aid of which tlie animal is able to cause a friction of any 

 power on the resonant vesicle. The foot is completely unarmed 

 in all its parts, the haustellum almost absent, the antennae too soft to 

 cause any compression ; the forehead flattened and simply roughened, has 

 Hot, as in that of Ghelonia pudica, those strong corneous teeth, which, 

 however, cannot be brought in contact with the musical organ. No 

 cause, then, appearing externally, it is evidently in the interior of the 

 drum that the bow, or rather the clapper, which produces the sound 

 must work ; for, if we may judge from its nature, it will be produced by 

 percussion, rather than by friction. If we open the vesicle, we see 

 that it is separated into two parts by a membranous division : the right 

 cavity is absolutely empty ; the left, deeper, it is true, and more 

 difficult to explore, appears to me, however, to contain no particular 

 organ, and in any case, no body tliat is able to be used as a hammer. 

 One must then renounce the supposition of a percussive body. There 

 remains the action of the air ; and for my part, without asserting any- 

 thing, this is the mechanism which appeal's to me the most probable. 

 The membrane which covers tlie apparatus is thin and flexible, and at 

 the same time of the consistence of talc or parchment ; one is able to 

 bend it at pleasure, and as soon as the pressure placed upon it ceases, it 

 resumes its original position with elasticity. It is, then, I think, by 

 rumpling {froissemenf) that the sound is produced. It may be that 

 the insect, contracting its pectoral organs, bends and unbends the 

 membrane alternately ; it may be, which to me appears the most 

 probable, that it is endowed with the means of causing momentary 

 emptiness — at any rate partially — in the cavity of the apparatus, by 

 inhaling a portion of the air that it contains, which being made to re- 

 enter the membrane, has the effect of inflating it anew by a sudden expira- 

 tion. Every one is able, as we know, to cause with the mouth these two 

 opposite movements in a dry bladder, and to produce, by this means, a 

 dry and piercing noise, quite analagous to that of the Setina. I leave 

 these suppositions to the reflections of Entomologists. 



[Has any British Entomologist ever observed these sounds in 

 Setina irroreUa ? The vesicles so minutely described by M. Guenee 

 are very conspicuous in that species, and I have seen them also in speci- 

 mens of 8. aurita and S. Andercggii, which I owe to the kindness of 

 M. J. Eallou. May I ask that Entomologists will follow up this most 

 interesting question, and endeavour to ascertain, if possible, whether 

 M. Guenoe's supposition, as to the means by which the sound is pro- 

 duced, be correct? —R. McLachlan.] 



