332 The Large Poplar Longhom 



gradually works its way down the centre of the stem to the exit portion 

 of the gallery. Clearing away the frass of the exit portion, and at the 

 same time widening and rounding off its outline, the adult fin all v 

 reaches the outside and issues through the now circular exit or 

 flight hole. 



If such a gallery as that described be made on a very young stem, say 

 a stem about five years old. one finds that the whole of the wood in the 

 centre of that portion of the stem between the exit portion and the 

 pupal chamber has been cut out, and only a thin outer shell 

 remains. 



Another form of gallery is that shown in Fig. 24; a modification of 

 the form just described; it may be found in older stems. Here the larva, 

 after tunnelling the horizontal portion of the gallery, turns at first down- 

 wards for a short distance and then returns and tunnels upwards, 

 gnawing deeper and deeper into the sapwood, until the centre of the 

 stem is reached. Before pupating, the larva cuts the exit portion at the 

 upper end of the gallery, pupating as in the case of the typical form. 



Irregular Larval Galleries (Plates XXI and XXII). 



Where many larvae are at work together on a stem, their galleries 

 may be very irregular both in shape and in direction. In fact, in many 

 cases it is extremely difficult, and may be impossible, to trace an in- 

 dividual gallery at all. As some of the less irregular forms are merely 

 modifications of the typical gallery, I propose to describe the parts of 

 them in so far as they differ from the forms already described. 



A specially common case is where the centre of the stem has already 

 been tunnelled by an older larva. Here, the younger larva cuts the 

 vertical portion of the gallery in the wood alongside the gallery already 

 cut in the centre of the stem. In other respects the gallery cut vertically 

 upwards by the younger larva resembles that of the typical form of 

 gallery, only it is much shorter. Whereas the typical form of gallery 

 cut in the pith may reach a length of almost 2 ft., it may only reach 

 9 inches in the irregular form. The outline too of the gallery when cut 

 in the wood is different from that when cut in the pith. In the case of 

 the former it is oval, elliptical or irregular in section, whereas in the 

 latter it is almost circular. 



In other cases occurring under similar circumstances to the last, but 

 where old flight holes' are already present on the stems, and within easy 

 reach of the younger larvae, no exit hole is cut, the future imagines 

 issuing through old flight holes. On young stems of about five years of 



