Mechanisms of Activity -- Regulation of Hox Activity: Insights from Protein Motifs -- Cis-Regulation in the Drosophila Bithorax Complex -- Maintenance of Hox Gene Expression Patterns -- Control of Vertebrate Hox Clusters by Remote and Global Cis-Acting Regulatory Sequences -- Evolution of Hox Genes and Complexes -- The Early Evolution of Hox Genes: A Battle of Belief? -- Evolution of Hox Complexes -- The Nematode Story: Hox Gene Loss and Rapid Evolution -- Are the Deuterostome Posterior Hox Genes a Fast-Evolving Class? -- Biological Function -- Hox Genes and the Body Plans of Chelicerates and Pycnogonids -- Hox3/zen and the Evolution of Extraembryonic Epithelia in Insects -- Hox Genes and Brain Development in Drosophila -- Homeosis and Beyond. What Is the Function of the Hox Genes?. In his 1894 book, Materials for the Study of Variation, William Bateson coined the term Homoeosis with the following prose: The case of the modification of the antenna of an insect into a foot, of the eye of a Crustacean into an antenna, of a petal into a stamen, and the like, are examples of the same kind. It is desirable and indeed necessary that such Variations, which consist in the assumption by one member of a Meristic series, of the form or characters proper to other members of the series, should be recognized as constituting a distinct group of phenomena. ...I therefore propose...the term HOMOEOSIS...; for the essential phenomenon is not that there has merely been a change, but that something has been changed into the likeness of something else. The book was intended as a listing of the kinds of naturally occurring variation that could act as a substrate for the evolutionary process and Bateson took his examples from collections, both private and in museums, of materials displaying morphological oddities. Interestingly the person who also coined the term "Genetics" proffered little in the way of speculation on the possible genetic underpinnings of these oddities. It wasn't until the early part of the next century that these changes in meristic series were shown to be heritable.