128 SEA-SHORE LIFE 
of wood, excepting palmetto logs or teak. The ship-worm begins 
to burrow into the wood by movements of its foot and shell, when 
only as large as a pin’s head, so that the opening to the burrow 
is small. Fora short distance from the entrance inward the bur- 
row is apt to be perpendicular to the surface, but it soon turns 
and runs more or less in the direction of the grain of the wood, 
although usually quite twisted. The burrow is lined with shelly 
material secreted by the teredo, and it is interesting to observe that 
no matter how numerous the teredos infesting a piece of wood, their 
tubes remain separate one from another and never intersect. The 
shelly material lining the tube is not the true shell of the teredo. 
The true shell is found at the head-end of the body which is farthest 
in from the opening to the burrow. Its two valves are small, 
white and delicately sculptured. The long, worm-shaped body is yel- 
lowish-white and tapers gradually to the posterior end which is 
near the opening of the burrow. The two long, extensible siphons 
are found here; and on both sides near their base are a pair of 

Fig. 88; SHIP-WORM with SIPHONS PROTRUDING, From living specimens infesting 
wood in the New York Aquarium, 
shelly flappers which serve to close the opening of the burrow 
when the siphons are withdrawn. A thick muscular collar at the 
base of the flapper also assists in closing the opening. 
The teredo does not eat the wood into which it bores and is, 
therefore, but little affected by poisoning the timber. The most 
efficient protection is copper sheating. Species of teredo are widely 
distributed and do enormous damage to submerged timber. Tere- 
