136 THE SEAS 



its relatives such as the cockle and mussel. When taken 

 out of its burrow and examined, the Shipworm, as shown 

 in Figure 27, is seen to consist of a long, naked body with 

 at one end a pair of small, peculiarly shaped shell valves, 

 and at the other a pair of delicate tubes or " siphons." 

 The former is the front end of the animal, it lies at the inner 

 end of the burrow and possesses the boring organs and the 

 mouth. The siphons are the only part of the animal which 

 projects from the burrow ; they are instantly withdrawn 

 when they are touched and the opening of the burrow — 

 not much larger than a pinhead — is closed by the pushing 

 forward of a pair of shelly, club-shaped " pallets " which 

 are fastened to the hind end of the animal about the 1 ase 



e.s. 



I.S. 



Fig. 27. — Shipworm (Teredo) out of burrow (slighly reduced) ; 



e.s. and i.s.. Siphons for taking in water ; /., foot ; 



p., pallets for closing opening ; s., shell. 



of the siphons. Within the body the organs are greatly 

 extended as a result of the elongated shape of the animal. 

 The principal organs are near the front end, but along the 

 entire length there stretches a cavity divided down the 

 centre by a delicate lattice-work of tissue. Water enters 

 the body of the animal through one of the siphons and 

 passes into one of these divisions, it is then filtered through 

 the lattice-work, leaving behind it any food particles which 

 are carried to the mouth, passing into the second chamber 

 from which it is expelled by way of the other siphon. In 

 this way the animal obtains both oxygen for respiration and 

 a certain amount of food. 



