National Geographic : 1969 Mar
but are very dissimilar animals-the cham bered nautilus and the paper nautilus. Aristotle first conjured up the charming picture of the paper nautilus resting con tentedly in its boat-shaped shell and holding its two bladed arms, like tiny sails, before the wind, while using its other arms as steering oars. People believed it for years. Actually, the shell of the paper nautilus (page 402) is a fragile shelter secreted by the two paddle-shaped arms of the female. The delicate case holds the animal and her eggs, its buoyancy preventing them from sinking. The chambered nautilus, on the other hand, swims near the ocean bottom inside a heavy shell. It has a doormat of 60 to 90 suckerless tentacles with which to capture fish and shell fish (page 409). Among other unique features it has eyes without lenses-one of the few ex amples in nature of visual organs that operate on the principle of the pinhole camera. Mathematicians and poets love the cham bered nautilus, the former because of the near-perfect geometry of its spiral growth.* As for poets, Oliver Wendell Holmes enshrined the chambered nautilus forever as an inspi ration for human striving (page 408). The *The fascinating architecture of mollusks was illus trated in "X-Rays Reveal the Inner Beauty of Shells," by Hilary B. Moore, NATIONAL GEOGRAPHIC, March 1955.