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Much has been learnt over the past six to seven decades about the development of vertebrate limbs from studies on embryos of the domestic chicken, Gallus domesticus. Early limb bud development is under the control of an epithelial–mesenchymal interaction between limb bud mesoderm and an apical epithelial ridge (AER). In this chapter we discuss the consequences for limb development in normal and mutant chick embryos of adding or deleting an AER.

Publisher Summary Methanocaldococcus ( Methanococcus ) jannaschii strain JAL-1 is a hyperthermophilic methanogenic archaeon that was isolated from surface material collected at a “white smoker” chimney at a depth of 2600 m in the East Pacific Rise near the western coast of Mexico. Cells are irregular cocci possessing polar bundles of flagella. The cell envelope is composed of a cytoplasmic membrane and a protein surface layer. Similar isolates have been obtained from hydrothermally active sediments in the Guaymas Basin and the Mid-Atlantic Ridge, and related species have been found at other marine hydrothermal vents. Because these hyperthermophilic species are very different from the mesophilic methanococci, they have been reclassified into a new family, Methanocaldococcaceae , and two new genera, Methanocaldococcus and Methanotorris . The characteristics of the source material for these isolates suggest that they possess adaptations for growth at high temperature and pressure as well as moderate salinity.