THE SHIPWORM. 109 



mollusc burrows into the husks of cocoa-nuts, and other thick 

 woody fruits which may be found floating in the tropical seas. 

 In consequence of the locality which it selects for its habitation, 

 it cannot proceed in one direction for any great distance, and is 

 obliged to make its burrows in a crooked form, which has earned 

 for the creature the specific title of corniformis, or horn-shaped. 

 Fossil woods are often found perforated with these burrows. 



Destructive as it may be. the Shipworm wiU ever be an object 

 of interest to Englishmen, inasmuch as its shell-lined burrow 

 gave to Sir I. Brunei the idea which was afterwards so efficiently 

 carried out in the Thames Tunnel. And, though from the 

 alteration of surrounding circumstances, that wonderful monu- 

 ment of engineering skill has not been so practically useful as 

 was anticipated, it has proved of incalculable value as pioneer to 

 the numerous railway tunnels of this and other countries. 



The largest species of this curious genus is the Giant Teeedo 

 {Teredo gigantea), which produces a shell more than five feet in 

 length, and three inches in diameter. The substance of the shell 

 is of very great strength, being about half an inch in thickness, 

 radiated in structure, and so hard that when the first specimen 

 was brought to England many naturalists took it for a hoUow 

 stalactite. 



This creature is a burrower into mud, and was discovered in 

 a very curious manner. In the year 1797, a violent shock of 

 earthquake took place in Sumatra, and caused great upheavals of 

 earth and corresponding floods of water. When the sea receded 

 from one of the bays, certain unknown objects were seen pro- 

 truding from its muddy bed, and were pulled out with tolerable 

 ease. They projected about eight or ten inches from the mud, 

 and as the projecting portions were beset by serpulse, bivalves, 

 and other marine parasites, it was evident that they were not 

 forced out of the mud by the shock, but had been in that posi- 

 tion for a considerable time. AU, however, were damaged, one 

 or both ends being broken off. Their colour was pure white on 

 the exterior, and yellowish within. None of them were per- 

 fectly straight, and the greater number more or less contorted. 



