When the shipworm is quite small it is not in the least like the perfect animal. Indeed, if you were to see a baby shipworm, I do not think that you would ever guess what it was. It is really a kind of shipworm caterpillar. In shape it is nearly round, and is covered almost all over with tiny hair-like organs, by means of which it swims in the water. But the odd thing about it is that it keeps on changing its form. After about thirty-six hours it becomes oval. A few hours later, if you were to look at it again, you would find that it was almost triangular. A few hours later still it would be round again, just as it was when it first hatched out of the egg. And during this time of its life it has a strong fleshy “foot,” like that of a snail, so that if it becomes tired of swimming it can settle down and crawl about on the surface of the rocks.
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.
1. THE RAZOR.2. TOP OF RAZOR FROM FRONT.
3. THE SABRE RAZOR.