DAMAGE CAUSED BY ANIMALS. 133 



copulatrix. Here the act of fructification of the female takes 

 place, and hence proceed the main galleries of equal breadth, 

 which are characteristic of the Scolytidte, (the breadth being in 

 each instance dependent on the size of the beetle), and along 

 which the female deposits her eggs alternately right and left in 

 small holes bitten out for the purpose. It less frequently hap- 

 pens that the ova are deposited in clusters. 



The Main galleries occur partly in the cambial layer between 

 the wood and the bark, being now more in the former, or 

 again more in the latter (bark-galleries), and partly in the sap- 

 wood itself (wood-galleries) ; they constitute the main difference 

 between the beetles which breed in the bark and those which 

 breed in the wood, and are distinguishable, according to the 

 direction they take, into : 



1. Vertical or longitudinal galleries, running in the axial direction 



of the stem. 



2. Horizontal or latitudinal galleries, when spreading peri- 



pherally round the stem. 



3. Radiating or star-shaped galleries, when radiating in con- 



siderable numbers from the camera copulatrix forming 

 the central point. 



The two first-named species of galleries have either one or two 

 branches, according as they go only to one or to both sides from 

 the entrance-hole bored into the stem. 



From the ova, whose number is often very considerable, (some- 

 times up to 100), and all of which are deposited within about 3 to 4 

 weeks, the larvae, (developed in about 14 days and issuing feetless, 

 curled in at the ends towards the belly, dirty-white in colour 

 with a brown head), begin to eat larval galleries almost at right 

 angles from the main gallery. These are small and narrow at first 

 but gradually enlarge in breadth and depth as the larvae 

 develop in size ; at the termination of each a pupal chamber 

 is scooped out for the inhabitation of the chrysalis. Whilst 

 growing broader, the larval galleries always spread out further 

 from one another, and deviate more and more from their original 

 direction perpendicular to the main gallery, so that the longest 

 of them sometimes at last run almost parallel to the latter. 

 As a rule, every larva has its own gallery, and in boring, the 

 larvae instinctively know very well how to keep clear of the 

 galleries formed by their neighbours on each side. 



