SEA- WORMS. 183 



comb with long teeth. Besides the gills, you observe a 

 conical body on a stem, with its apex downwards, and while 

 wondering what it is, the animal, perhaps alarmed, furls his 

 fan and pops into his hole. Now you see the use of this 

 organ ; for when the worm has drawn his breathing appara- 

 tus safely into the tube, he shuts himself in by drawing this 

 conical body after him and enclosing the aperture. It is, in 

 short, a stopper. He had a pair of tentacles ; one of them 

 remained small and undeveloped, while the other was ex- 

 panded and developed for the admirable use to which we 

 have seen it put. 



But how does the Serpula manage to creep up and down 

 his shelly tube so rapidly, withdrawing so instantaneously 

 when alarmed or disturbed? Alonsj the sides of his bodv 

 are seven pairs of tubercles, with a bunch of bristles in each, 

 which may be pushed out or withdrawn. Each bristle, 

 when microscopically examined, is seen to be " a transparent, 

 horny, yellow shaft, the extremity of which dilates into a 

 slightly enlarged knob. This is cleft into four points, three 

 of which are minute, but the fourth is developed into a long, 

 slightly divergent, highly elastic, tapering and finely pointed 

 spear." By pushing these bristles against the sides of the 

 tube, and prizing up the body by their means, the upward 



