302 TEREDO, OR SHIP-WORM. 



But the acute observer (Mr. J. V. Thompson) who first 

 discovered it, had the satisfaction of watching its 

 change from this active life to the sedentary state of 

 a Balanus. The animal fixes itself, the shell is gra- 

 dually formed, ciliated arms or cirrhi take the place of 

 feet, and the eyes are cast away, as being no longer 

 needed. Here we have another mstance of what looks 

 like a retrograde development ; but this apparent 

 anomaly is to conduct us to a division of the animal 

 kingdom in which the external organs are less perfect 

 than in the groups below them, but the internal or- 

 ganization, and especially the nervous system, is more 

 complete. 



Barnacles attach themselves to the surface of ships' 

 timbers, and their pendant bodies, if suffered to remain 

 will materially obstruct the ship's motion or way. But 

 they do no further damage. There are, however, other 

 Mollusca ,the Teredines, or Ship-worms, whose attacks 

 are far more fatal. These are not contented with a su- 

 perficial station, but seek a secure resting-place within 

 the log; and, when once they take up their residence, 

 soon riddle the substance through and through, reducing 

 the wood to a mere shell. Any wood-work constantly 

 submerged is subject to their attacks, and it is asto- 

 nishing with what rapidity the work of destruction 

 goes on. Piles of solid pine-timber of large size have 

 been proved to be perfectly destroyed in five years. 

 The Teredo enters at any part of the surface, but soon 

 bends its course in the direction of the grain, and 

 forms a burrow some feet in length, and varying from 

 a quarter to half an inch in diameter. This he lines, as 



