]
It follows the periphery so closely that the outer layer of growing
wood, separating it from the bark, does not average 0.25 mm. in
thickness, and yet I have never known it to cut entirely through this,
so as to lie in contact with the bark.
From this primary circular excavation issue, at right angles, and
generally in both directions (up and down), a varying number of
straight tubes, parallel to the axis of the plant (see Figs. 1, 2, and
3). They average five or six millimeters in length, and commonly
terminate blindly, a mature beetle being usually found in the end of
each. Sometimes, but rarely, one or more of those vertical excavations
is found to extend farther, and, bending at a right angle, to take a
turn around the circumference of the bush, thus constituting a second
horizontal circular canal from which, as from the primary one, a
varying number of short vertical tubes branch off. And in very
exceptional cases these excavations extend still deeper, and there may
be three, or even four, more or less complete circular canals. Such an
unusual state of things exists in the specimen from which Fig 3 is
taken.
[Illustration: FIGS. 3 and 4--Mines of Corthylus
punctatissimus.]
It will be seen that with few exceptions, the most important of which
is shown in Fig 4, all the excavations (including both the horizontal
canals and their vertical off shoots) are made in the sap-wood
immediately under the bark, and not in the hard and comparatively dry
central portion.
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