THE SHIP-WORM. 



437 



creature forms is either wholly or partially lined with shell, and it is worthy of notice 

 that the Shipworrn and its mode of burrowing was the object that gave Sir I. Brunei the 

 idea of the Thames Tunnel 



SHIP- WORM. Teredo navdlis. 



The Teredo did not always lead this fixed and darkling life, but at one time of its 

 existence it swam freely through the ocean, having organs of sight and hearing for the 

 purpose of guarding itself against the dangers of the deep. The following description of 

 the successive stages of this mollusc is from the pen of the able naturalist whom we have 

 already mentioned, and who has devoted much time to the study of the Ship-worm and 

 its habits. 



" The larva, which is at first almost spherical and entirely covered with vibratile cilia, 

 may be compared to a very minute hedgehog, in which every spine acts as a natatory 

 organ. It swims in all directions with extreme agility, and this first state continues about 

 a day and a half. Towards the end of this time the external skin bursts, and after being 

 encrusted with calcareous salts, becomes a shell, which is at first oval, then triangular, 

 and at last very nearly spherical. While the shell is being formed the vibratile ciliq 

 disappear, but the little animal is not on that account condemned to inactivity. In 

 proportion as the external cilia diminish we observe that another equally ciliated organ 

 becomes developed, which widens and extends in such a manner as to form a large collar 

 or ruff margined with fringes. This new organ of locomotion may be entirely concealed 

 within the shell, or may be extended from it, and acts in the manner of the paddle-wheel 

 of a steamboat. 



By means of this apparatus the young larva continues to swim with as much facility 

 as in its earlier age, but it now moreover requires another organ, which enables it to 

 advance upon a resisting plane, as, for instance, along the side of a glass vessel. This is a 

 sort of fleshy foot, very similar to a long and very mobile tongue, which can be extended 

 and contracted at will. The larva of the Teredo possesses, moreover, organs of hearing 

 similar to those of several molluscs, and eyes analogous to those of certain annelids. 



