16 Mr. T. V. Wollaston on certain Musical Curculionide. 
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 Curculionide 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 cliscover 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 ; 
