THE SHIP-WOEM. 125 



missioned to destroy. The Ship-worm (Teredo navalis), on the 

 contrary, always burrows with the grain, and even makes a trans- 

 verse tunnel, unless turned from its course by some obstacle, such, 

 as a nail, or the burrow of another Teredo. 



At first sight, few would perceive that the Ship-worm belongs 

 to the same class as the oyster and the snail, fpr it is long, slender, 

 and worm-like in shape, from six to eight lines in diameter, and 

 nearly a foot in length. One end is rather larger than the shaft, 

 if we may use the term, and is furnished with a pair of curved and 

 very narrow shell-valves, while the other is divided into a forked 

 apparatus containing the siphon. The color is grayish-white. 



Such is the aspect o#the Ship- worm when adult, but in its early 

 stages of existence it possesses a totally different form. When it 

 first issues from the sheltering mantle of its parent, it is a little, 

 round, lively object, covered with cilia, like a very minute hedge- 

 hog, and, by the continual movement of these appendages, passing 

 rapidly through the water. It does not, however, retain this form 

 for more than six-and-thirty hours, but undergoes a farther pro- 

 cess of development, and is then furnished with a distinct appara- 

 tus for swimming and crawling. It also possesses rudimentary 

 ejea, and in that portion of the body which may be considered 

 the head there are organs of hearing resembling those of certain 

 mollusks. "When it has passed its full time in this stage of devel- 

 opment, it fixes upon some favorable locality, and then undergoes 

 its last change, which transforms it into the worm-like moUusk 

 with which naturalists are so familiar. 



Ship-worm. 



