VOL. XXIV.J PHILOSOPHICAL TRANSACTIONS. 1^5 



it, but died. It is to be observed, that in those trees having their leaves green 

 and healthful, there was none of these flies to be found. 



About the middle of October I found that those small white maggots, and 

 consequently their channels, which they exactly filled, were grown much larger, 

 and they had made their progress from the place where they were first hatched, 

 which was close to, or upon the very wood of the tree, almost to the very 

 outside of the bark of the elm, which is usually pretty thick; and in every one 

 of the perpendicular channels before-mentioned, I found the mother fly lying 

 dead, for the most part towards the entrance of the said channel. 



These observations put me upon examining the wood which lay in my yard, 

 for timber or fuel, when in all the elm which was felled last spring, I found the 

 bark as much pierced; the same mother channel, and the same small channel, 

 proceeding from the mother channels, full of maggots, which had also made 

 their way almost to the outside of the bark. 



Observing some elm which had lain much longer in the yard, and taking off 

 the bark, I found the same tracks, both of mother fiy and maggots, and that 

 at the extremities of almost all the horizontal channels, made by the maggots, 

 where they had subsisted long enough to come to any perfection, the bark wa8 

 pierced quite through, by a hole just the size of the channel, and nothing left 

 remaining but a kind of whitish tough skin, exactly the colour and size of the 

 maggot, at the mouth of the hole, and the rest of the forsaken channel per- 

 fectly filled with dust or the excrement of the maggot. 



I then examined the ash wood, which had lain some time in the yard, and at 

 first sight, it being young, and its bark pretty smooth, I perceived it full of 

 »mall holes; and on separating it from the tree, I found just the same sort of 

 work as in the elm, and by the same sort of fiy, having found several of the 

 mother flies dead in their channels, and the same empty skins at the extremities 

 of the other channels; only with this difference, that whereas in the elm all the 

 mother channels were perpendicular, and the maggot channels horizontal, here 

 in the ash it was just contrary, all the mother channels were horizontal, and the 

 maggot channels perpendicular; this I at first thought might be accidental, and 

 peculiar to that piece of wood, but on examination of above 100 pieces of wood 

 of different trees, and felled at different times, I found it exactly to hold true 

 in them all. 



I observed several oak and maple trees, which had been felled, some in win* 

 ter and some in summer, and the bark remaining on them, but could find no 

 such thing in either of them. 



Fig. 18. pi. 7, shows the bark of ash: fig. IQ, the bark of the elm; fig. 20, 

 the worm as large as the life lying on its back; fig. 21, the mother fly, with its 



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