1G Mr. T. V. Wollaston on certain Musical Curculionictae. 



Longicorns of emitting a grating noise from their thoracic seg- 

 ments — the great central region of their body ; and as I had 

 formerly taken some pains to ascertain the precise nature of their 

 stridulating instrument as represented in the Atlantic genus 

 Deucalion, my first supposition was that this Canarian Acalles 

 had probably a similar mesothoracic file, over which the con- 

 stricted and roughened edge of the pronotum was made to slide 

 — an arrangement which I made out satisfactorily [vide Ins. 

 Mad. p. 432) in the D. desertorum, and which I thought might 

 possibly exist (although I had never hitherto suspected such a 

 fact) in certain members of the Curculionidce also. But on closely 

 examining the creature whilst producing its notes, I could per- 

 ceive no upward and downward movement of the head and pro- 

 thorax, such as is necessitated in the case of the Longicorns 

 whilst performing, and which causes the tuberculous inner sur- 

 face of the latter to sweep over the dorsal file of the mesonotum ; 

 nor, indeed, for a long time, could I detect any motion in the 

 body whatsoever. But at length a minute and rapid vibration 

 of the apical segment of the abdomen — so rapid that, to the 

 naked eye, it was scarcely appreciable — became evident, which 

 at once solved the mystery, so far indeed as it could be solved 

 without an actual dissection. 



And so the matter rested until now, when (after the lapse of 

 nearly a year) I have again taken it in hand, and have destroyed 

 a specimen of the Acalles argillosus, so as to discover the exact 

 nature of the mechanism on which its musical capabilities de- 

 pend ; and I feel bound to add that, although the structure is 

 so evident as to leave no doubt whatsoever on my mind as to the 

 modus operandi in generating the sound, it nevertheless seems to 

 me to be an instrument scarcely adequate to occasion notes thus 

 shrill and audible. In the Longicorns this was not so ; for there 

 the elongate file (in the form of an isosceles triangle) was ex- 

 tended along the whole length of the mesonotum, and was so 

 comparatively coarse and regular in its parallel ridges, that 

 it was not possible for a roughened surface (like the inner layer 

 of the pronotum) to slide across it without a noise of some kind 

 being produced. But in the case of the Acalles, the pygidium, 

 although roughened, is not very sensibly so ; whilst the small 

 portion of the inner surface of the elytra against which (at each 

 successive pulsation) it is brought to play is far less strictly file- 

 like than was the triangular mesothoracic space of Deucalion. 

 And yet this is certainly the contrivance by means of which this 

 little Curculionidous musician is enabled to perform its anal 

 " song." On carefully inspecting its abdomen, it will be seen 

 that the terminal portion of it (represented by a single visible 

 segment below, and by two when viewed from above) is free ; 



