BORING LIFE 137 



Now let us consider how it bores its way through the 

 wood. To understand this it is necessary to refer to 

 Figure 28 which shows the position of the boring organs 

 while they are in operation. Although many theories 

 have been advanced on the subject, it is now certain that 

 boring is carried out by the action of the small shell valves, 

 which are specially adapted for this purpose. As shown 

 in Figure 29, they are globular and can be divided into three 

 regions, a hinder portion in the form of a broad win? which 

 is known as the auric'e, a middle portion which forms the 



Fig. 28. — Head end of Shipworm (Teredo) lying in burrow ; 



b., body of worm : /., foot ; f.s., fold of skin above shell for gripping wood ; 



s., shell; t., edge of burrow. 



major part of the shell, and a portion in front of this which 

 only extends for less than half the width of the middle 

 portion and is then cut away sharply at right angles. The 

 surfaces of these two latter regions are covered with sharply- 

 pointed ridges, those on the former passing diagonally 

 across the anterior third of its surface, while those on the 

 latter run parallel to the sharply cut lower margin. Trans- 

 ferring our attention to the inner surface of the shell, we 

 see that there are two knobs, one at either extremity of 

 the middle region, while from the upper of these there hangs 



