6 2 THE POPULAR SCIENCE MONTHLY. 



or semitropical seas, though now it is found in high latitudes. It does 

 not appear to have been known to the Greeks or Romans, or at least 

 its ravages in ancient times could not have been very great, else the 

 unsheathed hulls of Greek and Roman vessels would have been per- 

 forated. The Pholas penetrates stone as well as wood, but the Teredo 

 loves most to burrow into timber. 



The damage done to submerged timbers by the Teredo is enormous. 



Fig. 2. 



Ttmbkr honey-combed by the Teredo. 



It once threatened the dikes of Holland with destruction. A portion 

 of the pier at Yarmouth was so honey-combed with perforations that 

 it might easily be crushed between the hands as though it were paper, 

 the partition between the various tubes being in many places as thin 

 as parchment. A piece broken off this pier, and measuring about 7 by 

 11 inches, weighed less than four ounces, including the shelly lining of 

 the tubes. In the space of 40 days a piece of deal was fairly riddled 

 by these borers, and Wood, in his " Natural History," gives an instance 

 of their attacking a floating block of oak. This block had a large iron 

 bolt passing through its centre, the rusting of which preserved the 

 timber for a small space all around from the attacks of the borers. 

 But all the block not so protected was honey-combed. 



The Ship-worm always makes its perforations in the direction of the 

 grain of the timber, except where a knot, or the shell of another Teredo, 

 or hindrance of any kind is met with, and then it takes a turn accord- 

 ing to circumstances. The animal begins to bore long before it has 

 reached its full size, and it grows within the cavity which it makes. 

 When taken out of the tube the Ship-worm is found to be a long, 

 grayish-white animal, about one foot long and half an inch thick, with 

 rounded head and forked tail. The Giant Teredo of Sumatra attains 

 the length of six feet, and a diameter of three inches. This animal, 

 however, differs from the Ship-worm in this, that it does not penetrate 

 timber, but only burrows into the hardened mud of the sea-bed. 



The use of copper-sheathing to protect ships from the Ship-worm is 

 so well known that it need but be simply referred to here. It is not 

 perhaps so generally known that, if timber be driven full of iron nails, 

 the same object is attained. Another method of protecting wood- 



