The small nematode Caenorhabditis elegans (C. elegans, 1 mm in length) originally was introduced into the laboratory in 1965 by Brenner (1) and has since become an important model organism. Caenorhabditis elegans for a variety of reasons offers excellent conditions for the study of basic features of life (2). C. elegans is surrounded by a rigid cuticula, which is, however, completely transparent. The adult organism is composed of a constant number of somatic cells (959 in the adult hermaphrodite, 1031 in the adult male), of which the complete cell lineage during development is known in all details (3). Altogether, this makes C. elegans a very suitable model organism to approach fundamental problems in development and aging.