40 College of Forestry. 
excavated by the larva (Fig. 27). In the part of the burrow 
first excavated, this frass is brownish in color showing its 
origin from the bark, in the middle part it consists of a 
mixture of brown bark and white sapwood, and in the later 
part of the burrow it consists nearly entirely of the white 
bits of sapwood. 
At the start the larval burrow is just wide enough to accom- 
modate the larva comfortably and increases in diameter with 
the growth of the larva, until at the time of pupation it is of 
about the same width as the egg gallery. The course of the 
larvae burrow is at first approximately at right angles to the 
ege gallery from which it originates. For the greater part 
of its length, it is usually continued in this same general 
direction, provided no obstructions such as other burrows, 
faults in the bark, or the bases of small dead limbs lie in its 
course (Figs. 27, 28). Toward the end, however, the course 
is likely to be more tortuous (Fig. 28). 
The length of the larval burrows varies considerably even 
in the same bark and when made by larvae from the same 
egg gallery (Fig. 27). Careful measurements were made 
of twenty larval burrows, only those being chosen which 
showed the entire burrow from the egg nitch to the com- 
pleted pupation chamber. The measurements were taken 
from the egg burrow to the farther side of the pupation 
cavity. Of the twenty burrows measured the shortest was 
18 mm., the longest 41 mm. and the average length was 
31 mm. Thirteen of the twenty were between 28 mm. and 
34 mm. long. 
The rate at which the larvae bore their burrows might be 
of interest. While no study was made with special reference 
to this matter, the very full notes on observations made from 
day to day furnish some instructive data. On the third day 
after hatching the burrow was 1.5 mm. long, on the seventh 
day 4.5 mm., on the twelfth day 13 mm. and on the seven- 
teenth day 20.5 mm. ‘These observations were made upon 
larvae of which the time of hatching was known within a 
very few hours. 
