160 INTERNAL ANATOMY OF INSECTS. 
sheath, two augers or borers, and an intermediate piece 
upon which they slide, each being furnished with an 
internal groove for that purpose, and the middle piece 
with a ridge to fit ; a contrivance of Divine Wisdom, 
to prevent their dislocation when employed in boring ; 
the augers terminate in a knob which is externally 
toothed *. This structure approaches that of the Hy- 
mcnoptcra, especially the saw-flies. With regard to 
the Heteropterous section of this Order — as they usually 
do not introduce their eggs into any substance, they have 
no call for any remarkable ovipositor, and therefore are 
not so furnished. A remark which will also apply to 
the Lepidoptera Order. 
In the Libellulina amongst the Newoptera, an organ 
of this kind is sometimes discoverable. In Agrion, Reau- 
mur noticed a part which he conjectured to be an ovi- 
positor ; it consists of four laminae or lancets, the interior 
pair slender, the exterior wider, and all externally ser- 
rated b . 
The insects of the Hymenoptcra Order have long been 
celebrated for the organs we are describing, whether 
used as saws, augers, or darts. I formerly gave you a 
very general account of the saws, — I shall now give you 
a very interesting one in detail copied from an admi- 
rable little essay of Professor Peck. " This instru- 
ment," says he, " is a very curious object ; and in order 
to describe it it will be proper to compare it with the 
tenon-saw used by cabinet-makers, which being made 
of a very thin plate of steel, is fitted with a back to pre- 
vent its bending. The back is a piece of iron, in which 
a narrow and deep groove is cut to receive the plate, 
Reaum. v. 177— . b Ibid. vi. 435. t. xl./. 6, 7. 
