In 1965 Sydney Brenner chose the free-living nematode Caenorhabditis elegans as a promising model system for a concerted genetic, ultrastructural, and behavioral attack on the development and function of a simple nervous system. Since then, with the help of a growing number of investigators, knowledge about the biology of "the worm" has accumulated at a steadily accelerating pace to the extent that C. elegans is now probably the most completely understood...