ANNELIDA, 240 



cement, which exudes from its skin, and whicli 

 unites the particles of sand into a kind of wall, or 

 coating. This covering does not adhere to the 

 body, but forms a detached coherent tube, within 

 which the animal moves with perfect freedom, and 

 which it leaves behind it as it progressively ad- 

 vances ; so that the passage is kept pervious 

 throughout its whole length by means of this lining, 

 which may be compared to the brick-work of the 

 shaft of a mine, or tunnel. 



An apparatus of a more complex description is 

 provided in the Terebella conchilega, belonging to 

 a tribe of marine worms, which from the peculiar 

 circumstances of their situation, inhabiting parts of 

 the shore nearly midway between high and low 

 water, are obliged often to prolong their tubes to a 

 great length through the sand ; for, in consequence 

 of the frequent shifting of the sands in storms, these 

 animals are sometimes buried to a considerable 

 depth, and at others have several inches of their 

 tubes exposed. In the one case, they must work 

 their way speedily to the surface ; in the other, they 

 must dive deeper below it. The manoeuvres of the 

 Terebella are best observed by taking it out of its 

 tube, and placing it under water upon sand. It is 

 then seen to unfold all the coils of its body, to 

 extend its tentacula in every direction, often to a 

 length exceeding an inch and a half, and to catch, 

 by their means, small fragments of shells, and the 

 larger particles of sand. These it drags towards 

 its head, carrying them behind the scales which 

 project from the anterior and lower part of the 

 head, where they are immediately cemented by the 

 glutinous matter which exudes from that part of 



