na 
(exxviti 
material through which it passes, dividing it more by splitting 
than by scratching, though it may at the same time, and, no 
doubt, does, lacerate them in more ways than one. Thus it is 
with that primitive type of plough, so well described by Virgil, 
and still, as I am assured, surviving in Italy, certainly till 
quite recently, and very likely to the present day. So it is 
with many other weapons and tools both artificial and natural, 
spear- and arrow-heads, pointed stakes, and conical bullets ; 
nails, screws, and drills ; tusks, horns, claws; and even the 
radicles of germinating plants. All these are essentially 
“ wedges,” and act accordingly. And it is to this class of tools 
—and not to that of tools which proceed, like a saw, by 
scratching particles loose and removing them in the form of 
sawdust—that I should refer the Sawfly’s implement, in 
consideration both of its form, when viewed all round, and 
not (as it too often is) in one aspect only—literally a ‘‘ one- 
sided view” !—and also of its actual progress through the 
material operated on, as I have repeatedly watched it in the 
operations of the living insect. 
I fear I am growing tedious, but I want to make clear one 
chief object of my Address. For the conception of the ideal 
saw, I want to substitute the conception of an elaborate and 
complex organ of quite another type—rather an ideal wedge, 
whose essential powers are supplemented by others, 7. e. it can 
rasp, scour, and otherwise lacerate, according to peculiarities 
of armature in particular cases ; but, on the whole, it cleaves 
its way, as a ship’s prow through the water, or a ploughshare 
through the soil. If I can make this point clear, I shall be 
able to say much of what remains to be said more briefly, and 
with less of tiresome detail. 
I shall now enumerate the separate pieces of which the 
complex organ, called as a whole the terebra, invariably con- 
sists. Of these there are ten in all, or it would perhaps be 
better to say jive pairs ; each piece being duplicated—simply, 
I believe, because of the general principle of bilateral sym- 
metry which we find in every insect-structure, and not because 
of any advantage which such duplication gives to the organ 
for performing its special functions. The same number of 
pieces, similarly duplicated, occur in the corresponding organs 
