The life cycle of the nematode Caenorhabditis elegans

The growth and reproduction of the small nematode Caenorhabditis elegans has been studied using an electronic nematode counter recently developed in our laboratory. At 20°C, the usual growth temperature, size increases in a smooth sigmoidal manner with time, linear growth being most rapid around the time of the fourth molt and nearly ceasing by the end of the period of egg-laying. Growth of populations is highly synchronous; the small residual size heterogeneity is maximal at about the time of maximal growth. The four molts do not involve major interruption of growth, but they do entail slight shape changes (elongating upon escape from the old cuticle). Egg-laying begins shortly after the fourth molt, the rate rising rapidly at first, then more gradually to a peak followed by a relatively rapid fall. Comparable measurements at 16 and 25°C establish that these are acceptable limit temperatures for work with temperature-sensitive mutants, although egg yield is somewhat reduced and the kinetics of egg-laying are altered at 25°C. Developmental chronologies for all three temperatures are presented.