q 
Snr rapes 
Life History of Tetropium gabrieli. 197 
ellipse was situated only slightly out of the perpendicular. In the 
ease of Callidiwm (violacewm, L., and variabile, L.) and other 
Longicornia I have observed the elliptical entrances to the burrows 
lie at all angles. In 6 ft. of a 7-in. wood-cylinder, in 240 holes 
of Tetropium examined, the ellipse, in three instances only, lay very 
slightly out of the perpendicular without any bend in the grain to 
influence the larva. 
I can assign no certain cause for this habit, unless it be a matter of 
convenience, which the arrangement of the wood-cells may account 
for. 
In Lari the latter are “ elongate, fusiform, with ends 
dovetailed between one another” (Veitch, Man. Conif., 
p. 82), and lie vertically to the circumference of the tree. 
From their formation the small bundles of these cells 
should be more easily picked up by the mandibles end- 
wise than across. If this is so the larva must needs work 
them in such an attitude as to cause the elliptical hole 
of entrance to lie vertically to the circumference of the tree. 
But this is not the case in the second and downward 
part of the burrow (Plate XVI, 0,¢, d), in excavating which 
the larva clearly lays hold of the wood-cells across. 
It may be that, having penetrated sufficiently far into 
the wood horizontally for its purpose, by the easiest 
method of biting the wood, at this point the strong instinct 
which impels the larva to pupate standing erect on the 
apex of the abdomen, necessitating the completion of the 
burrow and pupa-cell vertically to the circumference, or 
simply the greater convenience of a downward course, 
prevails, and the larva is content to lay hold of the wood- 
cells any way. 
It is interesting to note that in the only piece of wood 
(Scots Pine) by me at the time of writing infected by 
Criocephalus I observe that the elliptical holes of exit of 
the larva in the surface lie vertically to the circumference 
as the holes of eutrance of Tetropiwm. 
The normal burrow of Zetropiwm runs into the wood 
horizontally, or almost so, for about 1-2} in. (Plate XVI, 0), 
with generally a curve to the right or left or occasion- 
ally sinuating. It then takes a sharp turn downwards 
(Plate XVI, }), never upwards, for a distance of 1-24 in. 
At the bottom of this burrow is the pupa-cell. In the 
case of a tree which has been felled and is lying in a hori- 
zontal position at the time of the larva burrowing in the 
