220 MR WALTER RITCHIE ON THE STRUCTURE, BIONOMICS, AND 
Where the bark is somewhat thicker, pupation takes place in the bark or between the 
bark and the sap wood. Usually in the thicker-barked places pupation takes place in 
the bark itself. It was not uncommon, however, to find pupation in the bark even 
where the bark was thin, and in such places the pupae were close to the outside. So 
near the outside were the pupae in many cases that on the bark scales being removed 
pupae fell away. After pupation the new beetles eat their way out through the 
bark or through sapwood and bark. 
Overcrowding of mother galleries on badly infested stems occurs very frequently, 
and as a result these mother galleries are often very irregular in form (fig. 14). Some 
are one-armed, and, like the typical galleries, vary in length from If to 3 inches. In 
other cases one arm is much longer than the other ; for example, in a few cases examined 
the left arm measured inch, while the right arm measured 2j inches. These galleries, 
though irregular, always showed on dissection a number of eggs equal to what were 
found in a normal two-armed mother gallery. Some mother galleries cut into adjacent 
galleries, linking up with them, and in this way form a network girdling the stem. In 
such cases the larval galleries are also quite irregular. Where larval galleries ran 
into other larval galleries, and these latter continued as single galleries, the weaker 
larvse fell before the stronger. 
Another kind of irregularity is that found where the beetles have used for brood 
purposes felled stems left lying. In such a case I found (see fig. 15) that the entrance- 
holes were made on the upper exposed surface, and the females cut single-armed 
galleries. These were long, and always down the shady side. 
As will be seen from fig. 13, the brood galleries of M. piniperda are quite different 
from those of M. minor. The typical mother gallery is vertical, while the larval 
ones are horizontal. The length of the mother gallery of M. piniperda is variable. 
On standing stems I measured galleries varying in length from 3 to 7 inches. On felled 
stems the galleries were considerably longer. The mother gallery is somewhat bent at 
its commencement, broadening out slightly just underneath the bark for about ^ inch. 
The female, as in the case of M. minor , does all the work, laying eggs as she bores, and 
placing them in niches on either side. The eggs in a single mother gallery are much 
more numerous than in the case of M. minor. They vary in number from 50 to 120. 
The male throws out the bore meal that results from the gnawing of the female, and 
is usually found in the gallery behind her. 
The brood galleries, as in the case of M. minor , are in the inner bark layers, and 
are found more rarely cutting the sapwood. These larval galleries, like the mother 
galleries, vary also in length, measuring from 1^- to 3^- inches in length. When feed- 
ing is completed the larvse pupate. This pupation takes'place usually in the bark, 
but in cases where the bark is comparatively thin, between the bark and the sapwood. 
When ready to emerge the young beetles eat their way through the bark, leaving 
numerous flight holes. 
As in the case of M. minor, where overcrowding has taken place, say, on 
