THE GIANT TEREDO. 357 



principle on which many piers, etc., have been protected from this raollnsk. A large iron bolt 

 passes through the midst of the block, and the rust of the projecting head has spread itself 

 for some distance over the wood. Multitudes of holes, large and small, surround the bolt, but 

 not one has pierced that portion over which the rust extends. Knowing the objection enter- 

 tained by the Ship-worm to rust, engineers have been in the habit of driving a number of short 

 iron nails, with very wide heads, into the timber, arranging them in regular rows, with their 

 heads at no great distance from each other. The action of the salt water soon causes the rust 

 to spread over the spaces between the heads, and upon these spots the Ship-worm refuses to 

 settle. 



Another plan, and a very effective, though rather expensive one, consists in forcing a 

 solution of corrosive sublimate into the pores of the wood. This salt of mercury is very 

 destructive to animal life, and M. Quatrefages asserts that one twenty-millionth part of cor- 

 rosive sublimate is enough to destroy all the young Ship-worms in two hours, and that a 

 ten-millionth part would have the same effect in forty minutes. He therefore proposes that 

 ships should be cleared of this terrible pest by being taken into a closed dock, into which 

 a few handf uls of corrosive sublimate should be thrown and well mixed with the water. The 

 salts of copper and lead have a similar effect, but are not so rapid in their operation. The 

 wooden piles on which jetties and piers are supported can be preserved in the same manner. 

 Iron, however, is now rapidly superseding wood for such structures, and is quite impervious 

 to the attacks of any mollusk, no matter how sharp its teeth. 



When removed from the tube, the Ship-worm is seen to be a long grayish-white animal, 

 about one foot in length and half an inch in thickness. At one end there is a rounded head, 

 and at the other a forked tail. The burrow which the creature forms is either wholly or 

 partially lined with shell, and it is worthy of notice that the Ship- worm and its mode of 

 burrowing was the object that gave Sir I. Brunei the idea of the Thames Tunnel. 



The Teredo did not always lead this fixed and darkling life, but at one time of its exist- 

 ence it swam freely through the ocean, having organs of sight and hearing for the purpose of 

 guarding itself against the dangers of the deep. 



Of all shell-fish, the Teredo is the most important in its relations to commerce. Its 

 ravages are such that nothing short of an entire coating of copper plates on the hulls of 

 vessels will suffice to prevent the serious injury sure to come to them when exposed in 

 warm and temperate seas. On our coast, south of Cape Cod, spars and buoys are coated with 

 verdigris paint. 



It is an interesting fact that in the tropical regions, where the waters swarm with the eggs 

 of the Teredo, there flourishes the palmetto-tree, the wood of which is a perfect resistant to 

 the attack of the dreaded shell-fish. Piers are constructed of the palmetto logs, and prove of 

 immense importance in our Southern harbors. In the warm waters of the Gulf of Mexico, the 

 Ship-worms work with great rapidity. A pier of ordinary wood may seem to the eye wholly 

 sound. On close inspection of it there will be observed on the surface minute holes, which, 

 to the uninformed, are little suggestive of imperfection. Make a section of that wood, and we 

 will see the interior of the log wholly replaced by the white, hard shells of the creatures, which 

 entered in the young state, just before hatched upon the outer surface. These minute holes 

 show where each young shell-worm penetrated. From these points they progress, eating the 

 interior wood, and leaving nothing behind but the lime-shell tubes. Thus, when the pier seems 

 to the eye intact, its integrity is wholly destroyed ; the least jar or movement suffices to throw 

 the structure down. 



An enormous species of this genus, called from its dimensions the GIANT TEREDO (Teredo 

 ffigantea), has been found at Sumatra. This huge mollusk sometimes attains the length of 

 six feet, and a diameter of about three inches, but, fortunately for timber, does not make its 

 habitation in that substance, contenting itself with boring into the hardened mud of the sea- 

 bed. The color of the shelly tube is pure white externally and yellow within. On account 

 of its mud or sand burrowing habits, the specific title of arendria has been applied to this 

 species. 



