Have you ever been through the Thames tunnel? If you have, you will be interested to know that it is made just like a shipworm’s burrow, for a kind of boring instrument, called a “shield,” was made, which enabled the workmen to line the walls with masonry as fast as the earth was cut away. In this way the walls were prevented from falling in, and water from the river above was kept from breaking through the roof and flooding the tunnel. And Brunel, the great engineer who constructed the tunnel, admitted that the idea had come to him one day when he was examining the burrow of this wonderful mollusc. PLATE XIX THE RAZOR (1 and 2) If you walk about very quietly, when the tide is out, on the stretch of wet, sandy mud which lies just above low-water mark, you may often see a very curious object resting at the surface, and looking just like a little key-hole. And if you step heavily anywhere near it, it is almost sure to squirt up a little jet of water into the air and disappear. Then you may be quite sure that you have found the burrow of a Razor Shell. This is a very long, narrow creature with bivalve shells, which are shaped almost exactly like the handle of a razor. It is generally about four or five inches in length and half-an-inch in width, and the object which looks so like a key-hole consists of its siphon tubes, the tips of which rest just above the surface of the sand when it is lying at the mouth of its burrow. It digs by means of its strong, fleshy “foot,” just as the cockle does, and its burrow, which goes straight downwards just like a well, is often as much as two feet deep. So it is not a very easy thing to get a razor out of its tunnel. But if you want to do so I can tell you how to manage it. Just take a good big pinch of salt, and drop it down into the hole. Now the razor does not like salt at all, even though most of its life is spent at the bottom of the salt-water, and it comes up to the mouth of its burrow in a great hurry to get rid of it. Then if you make a very quick stroke with a spade you can dig it out before it has time to get down to the bottom again. But if you should fail to get it up at the first attempt it is of no use to try again, for even if you pour down a whole handful of salt the animal will never come up a second time. [Illustration: PLATE XIX 1. THE RAZOR. 2. TOP OF RAZOR FROM FRONT. 3. THE SABRE RAZOR.] The razor is very good to eat, if its tough leathery skin is slipped off, and on some parts of the coast it is often used for food. The fishermen use it for bait, too, and catch it by means of a slender iron rod with a barbed tip, which they thrust into its body as it lies at the bottom of its burrow. PLATE XIX THE SABRE RAZOR (3)