(exivir } 
scalpellum was moving. ‘Their advances and retreats in no 
way synchronised with the movements of the latter as a whole. 
And, so far as I could see, the movements of the two saws 
were independent of each other. They were certainly not 
simultaneous, nor did they seem to me—as both Réaumur 
and Vallisnieri state—to follow each other in regular alterna- 
tion. My impression was that each saw from time to time 
encountered and overcame more or less resistance from the 
material, and that the pace at which they were moving varied 
accordingly. During its descent the scalpellum as a whole 
occasionally slightly (but only very slightly) altered its 
direction ; now pressing its back, and now its sides, against 
the sides of the incision, and so widening the latter slightly 
in one direction or another. Thus it descended, till it was 
buried up to the hilt in a deep hole, or as it were a sheath, 
whose dimensions were practically identical with its own. 
At this point the modus operandi completely changed. Very 
slowly and gradually, and with occasional retreats in an 
opposite direction, the tip of the scalpellum began to move 
round in an arc towards the basal part of the insect’s venter, 
the saws all the time continuing to slide, so that they were 
cutting their way, and were also being carried by the 
supports, in the direction in which the whole instrument was 
now rotating. The effect of this was particularly conspicuous 
at the mouth of the incision, which could distinctly be seen 
to be growing gradually into a long clean-cut slit (situated 
longitudinally as regards the stem), Meanwhile, the insect’s 
abdomen, before quite straight, became a little hunched. Its 
tip, and accordingly also the base of the saw-sheath and that of 
the scalpellum itself, drew slowly more and more towards the 
thorax. ‘This movement pressed the cutting edges harder and 
harder against the tissues which they were severing, and the 
slit forming the mouth of the whole incision grew longer and 
longer. All the while, the whole serrated and denticulate 
edges of the “saws” were hard at work, sliding faster and 
faster, and being pushed harder and harder, in the direction 
towards which they were advancing, by the pressure from 
behind, caused by the movement which the instrument as a 
whole was making, viz. swinging round on its pivot-like (but 
K 2 
