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of the Aculeate Hymenoptera, where the function is quite 
different ; and also (as Lacaze-Duthiers has shown) in many 
insects belonging to other orders. Of these five pairs, three 
are completely chitinised, and these are visible at all times, as 
parts of the insect’s exoskeleton: they never actually enter 
themselves into the substances which are excavated, but serve 
only (1) to protect the two other pairs (which do enter the 
incisions) when they are not thus occupied, and (2) to com- 
municate to them certain of the movements which they have 
to make. 
Two of these chitinised pairs of pieces make up what is 
commonly called the “‘saw-sheath.” It is not, however, a 
sheath like that of a sword, enclosing the implement all round ; 
but only in the sense in which the handle of a clasp-knife 
might be called a “sheath” for its blade. The terebra, 
however, is in two respects at least unlike a clasp-knife ; inas- 
much as (1) when the blades become sheathed their cutting 
edges face outwards and not inwards, and (2) while sheathed 
it is concealed entirely. ‘The third pair of chitinised pieces 
appear to act as levers, producing movements (of advance and 
retreat alternately) in the cutting instrument itself. They are 
called, after Kriapelin, “the triangular plates.” 
As for the tool itself, it consists of two pairs of pieces—not 
completely chitinised, but partly corneous, and partly frail 
and membranous. As a whole, it is commonly called the 
ovipositor, and the ovipositor it is: but, regarded as to its 
penetrating functions, and its characters indicative of such 
functions, I shall venture to call it the Scalpellum—anglicé 
“penknife,” or (as surgeons term that type of blade) a 
‘ scalpel.” ; 
The upper (or posterior) pair, often called the “ supports,” 
are partially bound together above (by membrane at least), or 
even practically soldered together ; and are also articulated to 
the base of the ‘“saw-sheath,” and fied (by a wire-like pro- 
longation of their inferior thickened margins) to the body of the 
insect ; so that neither of them can advance, or retire, without 
being accompanied by the other, nor can they ever move away 
from the saw-sheath altogether, but only be rotated on its base, 
as on a pivot. Viewed from beneath, they appear as a 
