NATURAL HISTORY. 



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alarm down they all go, and then the task of obtaining them is a difficult 

 one. The common way of catching them is to try and grab them before 

 they are aware of the danger, or with a spade, to cut off the bottoms of 

 their burrows. These tubes are not vertical, but incline at an angle of 

 aboul sixty degrees, so that a spade stuck vertically behind a clam at the 

 ni,. nth of its burrow is pretty sure to cut off its retreat. 



The burrowing is peculiar: the process can readily be seen by placing 

 a live razor-fish on the surface of the sand. First the foot is protruded, 

 and its extremity drawn out into a sharp point, which is easily forced a 

 short distance into the sand. Next the fluids of the body are forced into, 

 the foot, swelling out the portion which just now was so sharp and slender 

 into an oval mass. This forces away the sand and also affords a foothold, 

 so that the process can be repeated, the sharpened tip of the foot now 

 being driven still farther into the soft sand. In a short time the burrow 

 is so deep that the shell is held upright, and then progress is even faster 



than before. 



The Teredo, or ship-worm, forms a marked contrast to all the molluscs 

 so far enumerated ; for while all these are of use to mankind, the Teredo 

 is a positive injury: indeed, it may be regarded as, of all molluscs, the 

 most injurious to human interests. It begins its life of destruction in a 



condition when one would hardly regard it 

 as injurious. At this time its general ap- 

 pearance is shown in our cut, — a small 

 spherical mollusc, not larger than the head 

 of a pin, with bivalve shell, long and slender 

 foot, and swimming freely through the water 



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by means of the circle of cilia projecting 



Fio.85. -Young of the ship-worm (Teredo), J ... 



before it begins its sedentary life, greatly from One end of the shell. Arrived at tlllS 

 enlarged. _ . 



condition, it must have wood or it dies. As 

 soon a- it obtains lodgment on a bit of timber, it begins its burrow, — how, 

 no one knows, — and is soon beneath the surface. Here it grows rather 

 rapidly, increasing more rapidly in size than in length, and excavating a 

 nearly cylindrical gallery, which it lines with lime, in the solid wood. It 

 does not teed upon the wood, as many have supposed, but receives its 

 nourishment through the hole by which it entered the wood. 



In this way hundreds of ship-worms will obtain entrance to the same 

 hit, nf timber, and will riddle it in every direction by their galleries; and 

 yet, strange to say, none of these tubes, no matter how contorted, will 

 encroach upon its fellows. How it is that one ship-worm realizes the 

 proximity of another, is a question. They also show a similar care against 

 breaking through the sides of the timber, so that while from the surface 



