The Decticus’ wing-cases widen at the base and form on the insect’s back a flat sunken surface shaped like an elongated triangle. This is the sounding-board. Here the left wing-case folds over the right and, when at rest, completely covers the latter’s musical apparatus. The most distinct and, from time immemorial, the best-known part of it is the mirror, thus called because of the shininess of its thin oval membrane, set in the frame of a nervure. It is very like the skin of a drum, of an exquisitely delicate tympanum, with this difference, that it sounds without being tapped. Nothing touches the mirror when the Decticus sings. Its vibrations are imparted to it after starting elsewhere. And how? I will tell you. Its edging is prolonged at the inner angle of the base by a wide, blunt tooth, furnished at the end with a more prominent and powerful fold than the other nervures distributed here and there. I will call this fold the friction-nervure. This is the starting-point of the concussion that makes the mirror resound. The evidence will appear when the remainder of the apparatus is known. This remainder, the motor mechanism, is on the left wing-case, covering the other with its flat edge. Outside, there is nothing remarkable, unless it be—and even then one has to be on the look-out for it—a sort of slightly slanting, transversal pad, which might very easily be taken for a thicker nervure than the others. But examine the lower surface through the magnifying-glass. The pad is much more than an ordinary nervure. It is an instrument of the highest precision, a magnificent indented bow, marvellously regular on its diminutive scale. Never did human industry, when cutting metal for the most delicate clockwork mechanism, achieve such perfection. Its shape is that of a curved spindle. From one end to the other there have been cut across this bow about eighty triangular teeth, which are very even and are of some hard, durable material, dark-brown in colour. The use of this mechanical gem is obvious. If we take a dead Decticus and lift the flat rim of the two wing-cases slightly in order to place them in the position which they occupy when sounding, we see the bow fitting its indentations to the terminal nervure which I have called the friction-nervure; we follow the line of teeth which, from end to end of the row, never swerve from the points to be set in motion; and, if the operation be done at all dexterously, the dead insect sings, that is to say, strikes a few of its clicking notes.