148 THE entomologist's record. 



much dislocated in fig. 1, except quite at their tips, much more so in 

 fig. 2. 



In fig. 1, one plate has the saw and support in the position of 

 rest, that is, their tips coincide ; the other plate has the saw somewhat 

 advanced. In fig. 2 both saws are advanced, but unequally. In the 

 movements of cutting, the saws are advanced rather more than the 

 most forward in fig. 2. 



The actual cutting movements difter, not essentially, but in detail, 

 very much from those of Trichiosoma. The actual cutting edge is the 

 margin of the "saws," chiefly towards their tips, and hardly, if at all, in 

 their basal halves. But in Tric/n'osovia the ends of the saws curl round 

 the ends of the guides and the cutting is done to a great extent by this 

 curled round tip. In Plujmatocera the saws remain all the time quite 

 straight, but in the sawing movements extend some way beyond the ends 

 •of the supports when advanced, being brought back to be level with 

 them when retracted. The two saws seem to be thus thrust forward 

 and retracted together, with, however, a differential to and fro move- 

 ment of the one on the other. This difterential movement of the saws 

 on each other is of much less amplitude than their conjoined move- 

 ment on the supports. 



In making the pocket, say as in diagram 2, the terebra moves 

 directly forward as a whole in cutting the deeper portion between 4 and 



5. In doing this 36 to and fro movements of the saws on the supports 

 were counted. From 5 to 6 the base of the terebra, i.e., the extremity of 

 the insect's body, moves little, and the terebra sweeps round to position 



6, making in doing so some 50 to and fro movements of the saws ; in 

 still sweeping round in much the same way to position 7 the basal 

 portion of the terebra gradually emerges from the pocket, and after 

 some 50 more strokes, this portion of the cutting is finished and the 

 terebra returns to the egg-laying position. 



During the last portion of the cutting, a curious detail, illustrating 

 the scissors-like process by which the two saws between them do the 

 cutting is easily seen. It may be most easily made intelligible by aid 

 of the very diagrammatic fig. 6, since, simple and obvious as it is 

 when seen, it is not easy to describe. 



The line a h c is that to which cutting is done, and as the terebra 

 sweeps forward, the body of the insect being the centre, the end of the 

 supports follows the dotted line (unfortunately omitted in Plate, it 

 should pass through the ends of the supports as it^ h, c does through 

 the ends of the saws), but the saws, continuing their thrusting and to 

 .and fro movements, gradually extend further and further beyond the 

 supports as at h and c, then by a movement of the insect the supports 

 slide down and resume at <■ the same relation to the saws that they 

 liad at a. 



In the straighter portions of the cutting the relative movements 

 ■&ve the same, but the supports remain at some distance from the lower 

 anargin of the pocket. 



What most interests me in these observations is their bearing on 

 the question as to how the cutting is really done by the terebra, is it 

 sawing, or cutting, or splitting, or by a wedge? They left on my mind 

 no doubt that the cutting is done not as by a knife or a wedge, but by 

 a scissors action, much as horse-clippers act. A number of projecting 

 edges on one saw continually pass too and fro across similar edges of 



