Figure 1.

The free-living nematode Caenorhabditis elegans, 1 mm long, grows on an agar plate, feeding on a lawn of Escherichia coli bacteria. (a) An experimenter selects an individual worm with a platinum wire. (b) A developing population with adults, juveniles and eggs. (c) Two adult worms mating, along with larval worms and eggs. The two sexes are a male and a self-fertile hermaphrodite, which is a female that makes 300 of its own sperm. The male, the smaller adult worm, has the copulatory organ at its tail anchored at the hermaphrodite mid-body vulva. Its sperm will also fertilize the hermaphrodite's eggs. Images provided by the author.