194 CONSTRUCTION OF THE TUBE 



with the twofold power of acting on the sucking 

 and muscular principle. 



'When the tentacle is about to seize an object, the 

 extremity is drawn in, in consequence of the sudden 

 reflux of fluid in the hollow interior. By this move- 

 ment a cup- shaped cavity is formed, in which the ob- 

 ject is securely held by atmospheric pressure. This 

 power is, however, immediately aided by the con- 

 traction of the circular muscular fibres. Such, then, 

 are the marvellous instruments by which these peace- 

 ful worms construct their habitation, and probably 

 sweep their vicinity for food.' 



The foregoing beautifully and accurately describes 

 the tentacular cirri. The use of these organs in the 

 formation of the tube in which the Annelid dwells, 

 I will now endeavour to make clear, from close 

 personal observation. 



It is an extremely interesting sight to watch a 

 Terebella extend its tentacles in all directions in 

 search of building materials, catching up the sur- 

 rounding molecules (sometimes visible along the 

 whole length of each filament), and then, by a strong 

 muscular contraction, bringing the collected atoms 

 to the opening of the tube, around which, as is gene- 

 rally supposed, they are then immediately attached 

 by a secretion which is exuded from the body of the 

 animal. Such, however, is not the case. 



When the filaments bring their ' subscriptions/ the 

 material thus gathered, instead of being used at once 



