“I very strongly recommend any of my readers who may obtain a female Sirex to disengage the actual borer from its two-bladed sheath, and examine it with the aid of a microscope. A half-inch object-glass will give quite a sufficient power.” [Illustration: ŒSTRUS. BORING TOOL OF SIREX AND LARVA.] [Illustration: AUGERS.] [Illustration: BRADAWLS.] “It is straight, stiff, and elastic, as if made of steel, and, if bent, will spring back to its proper form with the elasticity of a Toledo rapier. “But the borer possesses an auxiliary cutting apparatus which places it far above the rymer in point of efficacy. Even with an ordinary magnifying lens, it is easy to see that the end of the borer is developed into a sharp head, very much resembling that of a boarding-pike, and that the outline of the shaft is broken into a series of notches. “The half-inch glass, however, discloses a marvellous example of mechanical excellence. The head of the borer is then seen to be armed with long, sharp teeth, slightly curved inwards, and acting just as does the carpenter’s ordinary centrebit. “So much for the head of the borer: we will now turn to the shaft. “It appears that, in order to make a clean-cut hole for the reception of the egg, the shaft of the borer has to finish the task which the head begins. Accordingly, it is armed on each of its sides with a series of hard, sharp-edged ridges, running diagonally across it, and acting exactly as do the sharp ridges of a coffee-mill.” In point of fact, the ovipositor of the Sirex is the natural type of the improved gimlet of the present day. Instead, however, of having a single, spiral, sharp-edged groove running along the whole length of the shaft, it has a series of small, sharp blades, set exactly in the same line as is taken by the spiral groove, and acting in exactly the same manner--i.e. by cutting out successive portions of wood, and, by the diagonal position of the blades, throwing out the debris as fast as it is cut. I cannot but think that, if any modern tool manufacturer could take as his model the saw-like ovipositor of the Tenthredinidæ, and the auger-like ovipositor of the present insect, he would produce a series of most valuable implements, possessing powers far beyond those of ordinary tools. These short blades are arranged just like the “studs” on modern shells, and very much resemble them in shape, though not in material. * * * * * THE Auger finds also a natural representative in the ovipositor of an insect. That of the common Gad-fly (_Œstrus bovis_) is most beautifully constructed. It is tubular in form, and is of a telescopic nature, consisting of four tubes of different sizes, the smaller fitting into the larger just as is done with the joints of a common telescope, or those of a Japanese fishing-rod.