THE SIREX. 391 



" So much for the head of the borer : we will now turn to the 

 shaft. It appears that in ordei to make a clean-cut hole for 

 the reception of the egg, tlie 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. A more effective implement could not have been 

 invented, and the various boring instruments of modern days, 

 however novel they may appear to be, are in reality formed on 

 exactly the same principle as the borer of the Sirex, though 

 perhaps they may not carry out their object with such 

 perfection." 



The Uroceridse all deposit their eggs in trees, the ovipositor 

 first boring a tolerably deep hole, and then placing an egg at its 

 further extremity. As soon as the egg is hatched, the young 

 larva makes its way into the trunk of the tree, where it resides 

 for a considerable time, and causes much damage to the timber 

 by its perforations. Even in this country, where the Uroceridte 

 are comparatively scarce, whole plantations of fir-trees have 

 been very seriously injured, and in some cases the timber was 

 so filled with perforations that it was useless except for 

 firewood. 



There is much doubt among entomologists whether any of 

 the Uroceridae are genuine inhabitants of this country. A vast 

 amount of fir timber is annually imported, and in that timber 

 great numbers of the larvae have been known to exist. Con- 

 sequently, when they emerge in the perfect state and fly into 

 the open air, they instinctively search for growing fir-trees, and 

 proceed to deposit their eggs upon them. Another doubt exists, 

 or rather has existed, respecting these insects, some ento- 

 mologists thinking that the larvae do not feed upon the wood, 

 but upon the larvae of wood-eating beetles that had taken pos- 

 session of the tree. This conjecture is now considered to be 

 groundless, and it is certain that the structure of the head and 

 jaws is exactly such as would be required by a wood-boring 

 insect. Indeed, the larva of this insect looks almost exactly like 

 that of a wood-eating beetle. 



There is a curious point in the structure of the larval jaws. 

 Both are strong, horny, rather square in form, and armed with 

 several teeth and a large horny lobe. But one is compressed 



