THE SHIP-WORM OR TEREDO 405 



the sea beats into them, washes the dividing walls away, and the 

 face of the whole cliff comes down. Sea and mollusc together 

 succeed in accomplishing what the sea could but slowly perform 

 alone ; and peninsulas are slowly changed into islands by the com- 

 bined action of the two. 



Geologists tell us, indeed, that our own country was formerly 

 a part of the continent of Europe, and that it would possibly still 

 be joined to that continent if it had not been for the incessant 

 labours of the piddock. This shell-bearing mollusc has at least 

 helped to convert England into an island, and so to shape the 

 course of modern European history. 



THE SHIP-WORM OR TEREDO (Family Teredinid^) 



The Teredo or " Ship-worm " is to wood and wooden construc- 

 tions what the pholas is to limestone and other rocks. Indeed the 

 ship-worm and the pholas are so nearly allied that the former may 

 be described as only a long-drawn-out species of the latter. The 

 ship-worm also possesses its bivalve shell, but reduced to what we 

 might call a head-covering. 



A very odd thing about the ship-worm is, that it changes its 

 form as it increases in size. When first hatched out of the egg 

 it does not look like a worm, but reminds one of a very small 

 hedgehog; for its body is almost spherical, and is covered all 

 over with projecting hairs, or spines. At this stage of its life 

 it swims freely through the water. When it is about a day and 

 a half old its skin splits open, and hardens into a kind of shell. 

 Even this shell changes its form, however, for first it is oval in 

 shape, then it becomes triangular, and then again it alters until 

 it is nearly spherical once more. The animal has a projecting 

 " foot ", too, by means of which it can move about, after the 

 manner of the snail. Before long, however, it ceases its travels, 

 and fastens itself to some fixed object or floating log, after which 

 it rapidly develops the worm - like shape, and quickly becomes 

 a perfect ship-worm. 



As has been suggested, this curious creature does not bore into 



