Mollusk and Man. The Nautilus' Relation to the Human Embryo  Six
hundred meters deep, at the bottom of the ocean's floor, lies
the chambered nautilus, an ancient creature. The chambered
nautilus is a mollusk that dates back four-hundred fifty million
years and once ruled the open waters. For those that are
unfamiliar with the nautilus its most recognizable and memorable
characteristic is its shell. The nautilus has a coiled shell
that is lined with mother-of-pearl; it is divided into a series
of larger compartments, the most recent being the one in which
the creature resides. The nautilus regulates it's buoyancy
through the use of a tube that runs through the walls that
seperates the chambers called a siphuncle.  Right now you're
wondering, "Why would this person write something about this
boring creature?" The only thing about the nautilus that
interests me is it's shell. The nautilus' shell forms a golden
spiral. A golden spiral can be formed by placing quarter circles
in each square of a golden rectangle.