There is a huge saw of this kind in Chatham Dockyard. It is kept in a sort of cellar covered with flap doors, where it really has the air of some dread monster lying in wait for prey. A tree-trunk is brought for it to feed upon. The doors slowly open, the saw emerges, revolves so fast that the eye cannot detect the teeth, seizes on the tree-trunk, tears its way through with a scream and roar, and then sinks back into its cellar. I have often watched this saw in action, and have never been able to get over a kind of feeling that it was alive. [Illustration: SAWYER-BEETLE.] [Illustration: CIRCULAR SAW.] Now, if we suppose the saw to be pierced in the centre, and to have teeth on the inside instead of the outside, it would be equally efficacious; and, indeed, we have several tools used for cutting iron bars or pipes, that are constructed on a similar principle, though the cutting tooth revolves slowly instead of rapidly, and is urged by a lever handle. * * * * * THERE is in Nature a Circular Saw of just such a character, the teeth having their points directed inwards, and not outwards. In tropical America there are several large beetles which, like our Stag-beetle, feed upon the sap of trees, and obtain it by wounding the young branches with their jaws. One or two of them are pointed out as having the power of cutting a branch completely off by seizing it in their deeply toothed jaws, and flying round and round the branch so as to convert themselves into a circular saw. The late Mr. Waterton showed me a branch which had fallen on his head, and which was said to have been cut off by the Sawyer-beetle, as the insect is called. He did not actually see the insect at work, but he had no doubt that the natives were right who told him that it was the work of beetles’ jaws. Certainly the cut looked exactly as if it had been made in the way described. The branch was somewhat thicker than an ordinary walking-stick. The truth of this statement has often been denied, but I have ascertained from personal observers that it is literally true. A loud noise is produced by the operation, and, as the female is never seen to perform it, the general idea is that it is a call to its mate. TOOLS. CHAPTER III. BORING TOOLS.--STRIKING TOOLS.--GRASPING TOOLS.