388 
THE OCEAN WORLD. 
pauses, attacks the ligneous substance, and soon produces a little p° re ’ 
or cell, which will be the entrance to the future canal. 
Once fairly lodged in this little cell, 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 covei' 
ing, with two small holes for the passage of the syphon tubes. At- the 
end of three days this covering has become quite solid ; it is the con 1 ' 
mencement of the organized tube, in which the animal is to be de- 
veloped. When secured beneath this opaque screen, the little nn 111:1 
is no longer exposed to observation ; but if his cell is opened at the en 
of a few days, it is found that it has secreted a new shell, larger an 1 
more solid than the original one ; it is the shell of the adult aninud- 
The young Teredo, which feeds on the raspings of the wood, 1J1 ' 
creases rapidly ; it passes from first a spheroid form to an elongate 1 
shape, and when its body can no longer be contained in the shell, i 
projects boyond the edge, and would find itself naked were it 11(1 
protected by its membranous sheath, which adheres to the walls 0 
the ligneous channel, now the dwelling-place of the animal. 
The process by which a creature soft and naked like the here 
should break into a solid piece of the hardest wood so quickly, aD 
destroy it with so much facility, was long a mystery. Until very 
recently, the shell was looked on as the implement of perforat'* 011 ' 
But in that case the shell should preserve certain traces of its acti° n 
upon surfaces so resistent, as oak and fir ; but the shell, on the c011 
trary, is perfect, with no signs of friction. On the other hand, th 1 
muscular apparatus of the Teredo is not calculated to put the shell in * 0 
rotatory action, were the process a boring one. It does not seem tbei 0 
fore possible to attribute these perforations to a simple physical acti 011. 
Some naturalists have suggested, in explanation of this phenomenon 
that the animal is furnished with the means of secreting a hq 111 
capablo of dissolving the woody fibre. This has been met by ^ ^ 
statement that, in whatever way the wood is attacked, whether 
gallery is excavated with or across the fibre of the wood, the » l0 ^ c 
is as exactly and neatly cut as if it had been perforated by * ^ 
sharpest tool, and that a corroding dissolvent could not act with 
regularity, but would attack the harder and more tender parts ^ 
equally. This objection, which M. Quatrefages opposes to the ^ e ^j e 
a chemical solvent, appears to us to admit of no reply. But, w 
