322 



THE OCEAN WORLD. 



ment of spring. Four months after some fishennen, hoping to turn her 

 materials to advantage, raised the boat. But in that short space of 

 time the Teredos had committed such ravages that the planks and 

 timbers were riddled and worm-eaten so as to be totally useless." 



At the beginning of the eighteenth century, half the coast of 

 Holland was threatened with annihilation because the piles which 

 support its dikes and sea-walls were attacked by a 

 species of Teredo ; and it proved no contemptible 

 foe. Many hundreds of thousands of pounds were 

 expended in order to avert the threatened danger. 

 Fortunately, a closer attention to the habits of the 

 molluscs has brought a remedy to a most formidable 

 evil ; the mollusc has an inveterate antipathy to iron 

 rust, and timber impregnated by the oxide of iron is 

 safe from its ravages. The taste of the Teredo being 

 known, it is only necessary, in order to avoid this 

 dangerous mollusc, to sink the timber which is to be 

 submerged in a tank of prepared oxide of iron — 

 clothed, in short, in a thick cuirass of that antipathy 

 of the Teredo, iron rust. Ships' timbers are also 

 covered with the same protecting coating ; but the 

 copper in which ships' bottoms are usually sheathed 

 serves the same purpose. 



The singular Acephalous Mollusc known to natu- 

 ralists as the Teredo navalis, arid popularly as the Ship 

 Worm, has the appearance of a long worm without 

 articulations. Between the valves of a little shell, with 

 which it is provided anteriorly, may be seen a sort 

 of smooth rim, which surrounds a swelling projecting 

 pad or cushion. This cushion is the only part of the 

 Ijody of the animal which can be regarded as a foot. 

 Starting from this point, all the body of the Teredo 

 is enveloped by the shell and mantle, the latter of 

 which forms a sort of sheath communicating by two siphons with 

 the exterior (Fig. 128). 



The mantle adheres to the circumference of the shell. The tissue 

 of the mantle is of a greyish tint, very light, and transparent enough, 

 especially in the young, to permit of the mass of the liver, the ovary, 

 the branchise, and the heart being distinguished in the interior, even 

 to counting the pulsations of the latter. The siphons are extensile, and 

 attached the one to the other for about two-thirds of their length. 

 It is by these tubes that the aerated water enters which feeds the 



Fig. 128. 



Teredo navalis 



(Linnaeus). 



