es, considered together, can
move, lengthwise, in the groove that receives them; they can also move
one over the other, always lengthwise, so much so that, on the slide of
the microscope, their terminal points are seldom situated on the same
level.

If with our scissors we cut a piece of the inoculating-thread from the
living insect and examine the section under the magnifying-glass, we
shall see the inner groove lengthen out and project beyond the outer
groove and then go in again in turn, while from the wound there oozes
a tiny albimunous drop, doubtless proceeding from the liquid that gives
the egg the singular appendage to which we shall come presently. By
means of these longitudinal movements of the inner trench inside the
outer trench and of the sliding, one over the other, of the two portions
of the former, the egg can be despatched to the end of the ovipositor
notwithstanding the absence of any muscular contraction, which is
impossible in a horny conduit.

We have only to press the upper surface of the abdomen to see it
disjoint itself from the first segment, as though the insect had been
cut almost in two at that point. A wide gap or hiatus appears between
the first and second rings; and, under a thin membrane, the base of the
ovipositor bulges out, bent back into a stout hook. Here the filament
passes through the insect from end to end and emerges underneath. Its
issue is therefore near the base of the abdomen, instead of at the tip,
as usual. This curious arrangement has the effect of shortening the
lever-arm of the ovipositor and bringing the starting-point of the
filament nearer to the fulcrum, namely, the legs of the insect, and of
thus assisting the difficult task of inoculation by making the most of
the effort expended.

To sum up, the ovipositor when at rest goes round the abdomen. Starting
at the base, on the lower surface, it runs round the belly from front to
back and then returns from back to front on the upper surface, where it
ends at almost the same level as its starting-point. Its length is 14
millimetres. (.546 inch--Translator's Note.) This fixes the limit of the
depth which the probe is able to reach in the Mason-bee's nests.

One last word on the Leucopsis' weapon. In the dying insect, beheaded,
stripped of legs and wings, with a pin stuck through its body, the sides
of the fissure containing the inoculating-thread quiver violently, as
if the belly were going to open, divide in two along