268 THE WORLD OF THE SEA. 
extremities they thicken, and terminate in four sharp points, one 
of which projects beyond the others. When the creature feels 
disposed to go out of its case, it thrusts out of the foremost 
tubercles these sharp-pointed bristles ; these, pressing against the 
walls of the tube, urge the animal forward; then, contracting 
its body, it brings up the hindmost feet, and in the same way 
fixes these, so pushing itself forward. Invisible to the naked eye, 
there passes from each foot, perpendicular to the body, a fine, 
yellow ring. Under a strong magnifying power, the ring appears 
to be a ribbon, upon which rest triangular plates; each plate is 
armed with seven teeth—six turn in one direction, and the seventh 
faces them. There are 136 of these plates on each ribbon, and 
since there are as many ribbons as feet—that is, fourteen—there 
must be 1,904 of these prehensile plates, and each of them is moved 
by a distinct muscle. By this truly wonderful mechanism, the 
annelid can fix at once 13,328 teeth in the membrane which lines 
its tube. No wonder that it can with rapidity retreat when 
frightened, and no wonder that it cannot be drawn out of its 
home against its will! Even the most thoughtless must pause at 
this lavish expenditure of mechanism upon a mere worm which 
lives and dies far down in the ocean depths; and who can help 
exclaiming, “ Wonderful are thy works, O God; in wisdom hast 
thou made them all?” 
There is another member of this family—the Spzvorbis 
nautiloides—which also makes for itself a calcareous tube; but it 
is very fragile and weak, and generally is attached for support to 
some sea-weed or the shell of a mollusk. It secretes its pipe after 
a much more delicate fashion than the serpule, rolling the material 
round itself, somewhat after the plan upon which that fluviatile 
mollusk, the planorbis, manufactures its abode. The spirorbis is 
not much thicker than a pin’s head. It comes out of its tube 
from time to time, spreads its plume, and most gracefully do its 
tentacles wave its food into its mouth. It has no head, no eyes, 
no mandibles; but can hermetically close itself into its little 
mansion, like its larger relative, the serpula. 
The Zeredclla is also a tubicole annelid. It is peculiar for the 
number of yellow filiform appendages which spring from about 
the mouth; these the animal can stretch to a great length. From 
