The Problem of the Sirex 



vein with a better flavour; now, it makes a 

 short, straight, roomy corridor, leading with 

 a sharp bend to the outside world. It had 

 plenty of time during its capricious wander- 

 ings; the adult has none to spare: his days 

 are numbered; he must get out as quickly 

 as he can. Hence the shortest road and as 

 little encumbered by obstacles as is consistent 

 with safety. The grub knows that the too 

 sudden junction of the horizontal and the 

 vertical part would stop the stiff, inflexible 

 insect and bends it towards the outside with 

 a gentle curve. This elbow changing the 

 direction occurs whenever the larva ascends 

 from the depths; it is very short when the 

 nymphosis-chamber is next to the surface, but 

 continues for some length when the chamber 

 is well inside the trunk. In this case, the 

 path traced by the grub has so regular a 

 curve that you feel inclined to subject the 

 work to geometrical measurement. 



For want of sufficient data, I should have 

 left this elbow in the shadow of a note of 

 interrogation, had I had at my disposal only 

 the emergence-galleries of the Longicorns 

 and Buprestes, which are too short to lend 

 themselves to trustworthy examination with 

 the compasses. A lucky find provided me 

 with the factors required. This was the 



