THE TEREDO. 213 



other lamellibranchs, are free swimmers, quite unlike 

 the adult parents. After a brief and sportive life in 

 the water they find a post or a floating piece of wood, 

 and begin to bore a hole. 



At first this hole is very small, but as the creature 

 grows the hole increases in diameter also. As he 

 advances he lines the hole with shell, making a white 

 tube, ever increasing in size. Communication with 

 the outside water is kept up by the siphons, which 

 reach to the original entrance. Through these 

 siphons a current of circulation is kept in motion, 

 bringing in food and breath, and carrying away all 

 chips and refuse particles. 



If our borer finds that his hole is approaching the 

 tube of another of his species, he turns his course 

 and bores on through undisturbed wood. Thus it 

 happens that the timbers of which a wharf is built 

 may appear perfectly sound, when, in fact, they are 

 completely honey-combed. A little shock may 

 break them open, disclosing the mass of tortuous 

 tubes. 



The valves of the shell of this mollusk are at the 

 very front of the tube, and are nearly spherical in 

 shape. They gape widely at both ends. The front 

 of the shells is very beautifully sculptured, though 

 the markings are so fine that a microscope is needed 

 by which to examine them. There is an internal 

 spoon-shaped process in each valve as in all the Bor- 

 ers. There are also two peculiar, oar-shaped, shelly 

 appendages, which close the external opening of the 

 burrow and perhaps perforin other duties. The 

 globular shell of the Teredo is about half an inch in 

 diameter, and the pens or oars are some two inches in 

 length. 



