THE GIANT TEREDO. 357 
principle on which many piers, ete., have been protected from this mollusk. 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 handfuls 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. 
Tron, 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. Brunel 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 
gigantea), 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, 
