ANNELIDA. l.QO 



terlals, and not being orjranin produnllons of Ihr animals 

 themselves, are structures wholly foreign to their systems. 

 These inhabitants of tubes, the Tubicolae of Cuvier, are gene- 

 rally furnished with tentacula, issuing from the head, which, 

 when the rest of the body has retired within the tube, is the 

 only part exposed. 



The expedient resorted to for progressive motion by the 

 Lumbricns mariniis oi lumn^us {Jirenicola j)isc(tioriim of 

 Lamarck,) is very remarkable.* This worm, depicted in 

 Fig. 135, swarms on all sandy shores, and is dug up in great 

 numbers as bait by the fishermen. It bores its way through 

 the sand by means of the peculiar construction of the rin^-s 

 of its head, which, when elongated, has the shape of a re- 

 gular cone. As each ring is so much smaller than the one 

 behind it as to admit of being received within it, the whole 

 head, when completely retracted, presents a flat surface. 

 When this disk is applied to the sand, the animal, by gradu- 

 ally projecting the cone, and successively dilating the rings 

 of which it is composed, opens for itself a passage through the 

 sand, and then secures the sides of the passage from falling in 

 by applying to them a glutinous cement, which exudes from 

 its skin, and which 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 advances: so that the passage is kept per- 

 vious 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 Terebellx conchilegx, belonging to a tribe of marine 

 worms, which from the peculiar circumstances of their situa- 

 tion, 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 tiic sands in storms, these animals are 



♦ See the account given by Mr. Osier, Philosophical Ti-ansaclions fov 

 1826, p. 342. 



