THE TEREDO AND ITS DEPREDATIONS. 



.549 



chance (which, by-the-way, only secures such good fortune to very care- 

 ful observers) to seize the moment when an annelide, coming out of one 

 of the openings of wood, at once took possession of a teredo that he 

 had placed on the bottom of the vessel which held the wood. He saw 

 the annelide seize the teredo with his jaws, draw him into the canal 

 which he occupied, and devour him so completely that there only re- 

 mained the two valves of the shell. 



It is in an entirely different manner that the cirripeds (Balanus 

 sulcatus) aid in preserving wood. When these animals, to which sail- 

 ors and the inhabitants of our coasts give the name of Pustules of 

 the Sea, or Sea-Thorns, multiply to such an extent on the surface of 

 wood that their disks touch, without leaving the least vacant space, 

 the natural consequence is, that the young teredo cannot find any 

 place where it can attach itself, and hence it is impossible for him to 

 penetrate the wood. This preservative effect is produced even when 

 the shells have fallen, provided the disks adhere to the wood. 



III. 



On the Circumstances which favor the Ravages op the Te- 

 redo. The commission gave in its first report an historical epitome of 

 the injuries done by the teredo at different epochs in Holland. 



When the teredo was remarked for the first time, an idea prevailed 

 that it was imported from abroad ; vessels coming from the East Indies 

 were accused of having brought that destructive guest. Two facts 

 show the incorrectness of this idea. On the occasion of the deepening 

 of the Dumbart Dock at Belfast, William Thompson ' found, twelve 

 feet below the surface of the earth, in a blue, argillaceous soil, the 

 trunk of a tree entirely riddled by the teredo. Considering the depth 

 at which this debris was found, and the fact that it lay beneath a series 

 of strata of shells, it is certain that it was deposited there ages ago, 

 long before a vessel, coming from the East or West, could touch the 

 coast at Belfast. 



Fossil wood, perforated by the teredo, has been found in different 

 localities : for example, in the London clay, in the Eocene formations 

 at Brussels, where Van Beneden discovered fossil wood, inclosing the 

 remains of the teredo; and at considerable depth, also, near Ghent, at 

 the time of the construction of the citadel. 



The teredo existed in a geological period earlier than our own, and 

 he appears to have been always an inhabitant of our coast. Why is it, 

 then, that at certain epochs, as in the years 1730, 1770, 1827, 1858, 

 and 1859, he multiplied so prodigiously as to destroy entire dikes in a 

 very short space of time ? Even as early as 1733, Massuet assigned 

 as a cause an increase of the degree of saltness of the water, resulting 



i W. Thompson, on " The Teredo navalis and Limnoria terebrans" in Edinburgh 

 New Philosophical Journal for January, 1855. 



