The homoeo box is a conserved protein-coding DNA sequence present in several genes in arthropods, annelids and vertebrates1-4. Two distinct classes of homoeo box have been identified-the Antennapedia (Antp) class1,5 and the engrailed class6-8. In insects, both classes are found in genes involved in regulating development. We have therefore investigated the phylogenetic distribution of Antp-like homoeo boxes to explore the possibility of a link between their presence and developmental strategy1,9-11. The distribution data also give important insight into the origin of homoeo boxes and the phytogeny of the animal kingdom. © 1986 Nature Publishing Group.