Plate II. 
Fie. 2. Top of American larch with the outer bark 
removed, showing the burrows of Polygraphus rufipennis. 
Note the engravings with one, two and four egg-galleries. 
It will be seen that the egg-galleries are typically and nearly 
invariably transverse, while the larval mines are longitu- 
dinal. Reduced to seven-tenths natural size. 
Fie. 3. Burrows of P. rufipennis in the inner bark of 
the trunk of the American larch. Note the direction of the 
egg-galleries and the variation in the number of these in the 
different engravings. The bark even on the trunk of larch 
is relatively thin, and therefore the nuptial chamber is here 
at the juncture of inner bark and sapwood. Slhghtly less. 
than one-half natural size. 
Fic. 4. Burrows of P. rufipennis in the inner bark of red 
spruce. The bark here is thicker than in larch and the 
nuptial chambers of the burrows are therefore in the outer 
part of the inner bark and not visible. Reduced to about 
three-fourths natural size. 
Fie. 5. Section of the trunk of larch from which the 
greater part of the outer bark has been removed by wood- 
peckers, exposing numerous burrows of P. rufipennis and 
one burrow of Monohammus scutellatus. ‘These birds have 
acted as a partial check upon the borers, as a large per cent 
of the latter had been eaten by them; yet in spite of their 
work the number of borers which remained alive was con- 
siderably larger than the number originally entering the 
bark. Thus, while woodpeckers render efficient assistance in 
keeping down the numbers of boring insects, they cannot be 
depended upon to restore the balance of nature unless aided 
by artificial or by other natural factors. Reduced to about: 
two-fifths natural size. 
