C sexi, ») 
believe, by the entire terebra, inclusively of its chitinised and 
corneous pieces and the membranous connections uniting 
them. 
Of the chitinised paired “ pieces,” I refer the pair forming 
the apex of the ‘“‘saw-sheath” to the 10th uromere, those 
which form its base to the 9th, and the pair which act as 
levers (=the “triangular plates” of Kripelin) to the 8th. 
I draw this inference from their actual positions and attach- 
ments to one another, which I cannot account for to my 
own satisfaction on any other view: but I cannot pretend to 
have traced their ontogenetic development, which alone could 
settle the matter finally. Of the non-chitinised pairs, I refer 
the so-called ‘‘supports” to uromere 9, and the so-called 
‘‘saws” to uromere 8. But here, again, I have only studied 
the phenomena in the imago. 
I shall now make a few remarks on the movements which 
are mechanically possible to an organ constructed and situate 
as is the scalpellum, and which I have actually witnessed 
as made by or occurring in it. 1.—As a whole, it can be 
pushed by pressure from behind into any substance suffici- 
ently yielding, completely up to its hilt, i.e. up to its junction 
with the sheath ; but no farther, because the sheath never 
itself enters the incision. In this movement its part is 
entirely passive, as when a nail is driven home by taps or 
pressure on its head. 2.—Also as a whole (‘‘supports” and 
“saws” together, it can be rotated by muscles contained in 
the saw-sheath, the base of which serves it for a pivot. In 
this case, if the base of the saw-sheath remain stationary, the 
point of the scalpellum describes an are of a circle, but, if the 
pivot move the are described is (roughly speaking) that of 
an ellipse. (Bearing the above facts in mind, it becomes 
possible to calculate from the length of the scalpellum and 
the extent to which its base is known to move, the maximum 
depth and breadth of such an incision as can be formed by it.) 
3.—However the “supports” move, the “saws” must be 
carried along with them, moving in this respect only as 
passenger's, and not independently. 4.—The “supports” have 
no entirely independent motion, either together or separately ; 
except that, to a limited extent, they can stretch asunder 
