324 THE OCEAN WORLD. 
curious spectacle is observed of a being which fabricates, step by 
step and as it requires them, the organs necessary for the performance 
of its functions. It begins by creeping along the surface of the wood 
by means of the very long tubes with which it is furnished. Then it 1s 
observed from time to time to open and shut the valves of the little 
embryo shell which partly envelopes it. As soon as it has found a 
part of the wood sufficiently soft and porous for its purpose, it pauses, 
attacks the ligneous substance, and soon produces a little depression 
or opening, which will be the entrance to the future tunnel. 
Once fairly lodged in this little opening, the young Teredo is 
rapidly developed ; it covers itself with a coating of mucous matter, 
which, condensing by degrees, assumes a brownish tint, forming a 
solid covering, with two small holes for the passage of the siphon 
tubes. At the end of three days this covering has become quite 
solid ; it is the commencement of the calcareous tube, in which the 
animal is to attain its full size. When secured beneath this opaque 
screen, the little miner is no longer exposed to observation ; but 
if his cell is opened at the end of a few days, it is found that it has 
secreted a shell, larger and more solid than the original one; and 
this is the shell of the adult animal. 
The young Teredo, which feeds on the raspings of the wood, 
increases rapidly; it passes first from a spheroid form to an elongated 
shape, and when its body can no longer be contained in the shell, it 
projects beyond the edge, and would find itself naked were it not 
protected by its membranous sheath, which adheres to the walls of the 
ligneous channel, now the dwelling-place of the animal. 
The process by which a creature soft and naked like the Teredo 
should break into a solid piece of the hardest wood so quickly, and 
destroy it with so much facility, was long a mystery. Until very 
recently, the shell was looked on as the implement of perforation. 
But in that case the shell should preserve certain traces of its action 
upon surfaces so resistant as oak and fir; but the shell, on the con- 
trary, is in such cases perfect, with no signs of friction. On the other 
hand, the muscular apparatus of the Teredo is not well calculated to 
put the shell into rotatory action, were the process a boring one. It 
does not seem therefore possible to attribute these perforations to a 
simple physical action. 
‘Some naturalists have suggested, in explanation of this phenomenon, 
that the animal is furnished with the means of secreting a liquid 
capable of dissolving the woody fibre. This has been met by the 
statement that, in whatever way the wood is attacked, whether the 
gallery is excavated with or across the fibre of the wood, the groove 
