IF we want examples of exceedingly powerful pincers, we need only go to the Lobsters and Crabs, especially to the latter, whose claws are often of enormous thickness in proportion to the size of the animal. All those who have visited the seaside know how severe is the pinch of the common Green Crab, comparatively small though it be, and the same may be said of the river crayfish, which is, in fact, a lobster in miniature. As to the lobster itself, fishermen are so well acquainted with the power of its claws, that they tie them together with string as soon as the animal is caught. Formerly they used to “peg” them, _i.e._ drive a wooden peg into the joint so as to prevent it from moving. This custom, however, is now prohibited by law on account of its cruelty. The power of the Crab’s claws is so great that a bite from a large Crab will inflict a severe injury, and render a hand helpless. It has more than once happened that men who have been feeling for Crabs in the recesses of the rocks at low water have been seized, and seriously imperilled, not being able to release themselves from the gripe. Indeed, it is said that there have been instances where the Crab has held so tightly, that the man has been drowned by the returning tide, no one having come to his assistance. I am, however, inclined to doubt this statement, thinking that the Crab would not be likely to remain in its hiding-place very long after the water came up. Still, that such an idea should be currently believed in many parts of England shows the estimation in which the gripe of the Crab’s claw is held. TOOLS CHAPTER IV. POLISHING TOOLS.--MEASURING TOOLS. Files and Sand-papers.--The Sheffield File and its Structure.--The Equisetum, Mare’s Tail, or Dutch Rush.--Beauty of its Surface when seen through the Microscope.--Sand-paper.--Skin of Dog-fish, Skate, and Shark.--Skate-skin used for Sword-handles.--Distinction between the File and Sand-paper.--Measuring Tools.--The Plumb-rule and the Level.--Their Use in Tunnelling.--The Measure and its Uses.--The Two-foot Rule and the Tape Measure.--Ovipositor of Gall-fly.--Tongues of the Woodpecker, Wryneck, and Creeper.--The Spirit-level and its Uses.--Theodolite and Callipers in Nature and Art.--The Contouring-glass.--Pincers of Earwig again.--Jaws of Insects.--The great Sialis of Columbia. FILES AND SAND-PAPERS. Having now examined the analogies between the cutting, boring, striking and grasping tools of Nature and Art, we come to those finishing tools which smooth and polish the surface.