254 NATURE'S TEACHINGS. 



" 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, how- 

 ever, 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 posi- 

 tion 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 Ten- 

 thredinidae, and the auger-like ovipositor of the present insect, 

 he would produce a series of most valuable implements, possess- 

 ing 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 (CEstrm bovis] is most beauti- 

 fully 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. 



The end of the ovipositor is developed into little projections, 

 some of which are armed with hard, sharp points, which act 

 exactly like the cutting edge of the auger. This elaborate 

 appliance is necessary on account of the- thick, tough skin of 

 the ox, which the Gad-fly has to penetrate before it can deposit 

 its eggs. Perhaps the reader may be aware of the fact that 

 the modern system of cutting channels in stone with the 

 diamond point, as was so well exemplified in the Mont Cenis 

 Tunnel, is but an imitation, and an imperfect one, of the method 

 adopted by the Gad-fly. We shall soon recur to this instrument. 



