Studies of the nematode worm Caenorhabditis elegans have led to the widely held belief that individuals of a given nematode species are characterized by a property known as eutely, in which all individuals have the same total number of cells1. This property, which is peculiar to nematodes and a few other phyla, has raised the question of whether the developmental mechanisms of nematodes differ from those of larger metazoans. Here we show that many, perhaps most, nematode species are not eutelic in at least one organ, the epidermis, and that in this respect they resemble other model organisms such as fruitflies and mice.