154 INTERNAL ANATOMY OF INSECTS. 
dislocation when: employed in boring ;' the augers ter- 
minate in a knob which is externally toothed*, This 
structure approaches that of the Alymenoptera, 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 re- 
mark which will also apply to the Lepidoptera Order. 
In the Libellulina amongst the Neuroptera, 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 Jamine or lancets, the interior 
pair slender, the exterior wider, and all externally ser- 
rated®. ) 
The insects of the Hymenoptera 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,—lI 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, 
which is fixed: the saw of the Tenthredo is also furnished 
with a back, but the groove is inithe plate, and receives 
a prominent ridge of the back, which is not fixed, but 
permits the saw to slide forward and backward as it is 
a 
* Reaum. v. 177--. » Ibid. vi. 435. t. xl. f. 6, 7. 
