P.S. (10/4/10, 12:33 am)
A snail is born with its shell! From Wikipedia ("snail"):
At tignan mo nga naman! May math pa talaga sa shell ng snail! Amazing!
As the snail grows, so does its calcium carbonate shell. The shell grows additively, by the addition of new calcium carbonate, which is secreted by glands located in the snail's mantle. The new material is added to the edge of the shell aperture (the opening of the shell). Therefore the center of the shell's spiral was made when the snail was younger, and the outer part when the snail was older. When the snail reaches full adult size, it may build a thickened lip around the shell aperture. At this point the snail stops growing, and begins reproducing.
A snail's shell forms a logarithmic spiral. Most snail shells are right-handed, meaning that if the shell is held with the apex (the tip, or the juvenile whorls) pointing towards the observer, the spiral proceeds in a clockwise direction from the apex to the opening.