Deserts, whether hot or cold, are considered to be one of the most difficult environments for living systems, lacking the essential free water which ac counts for approximately 60-70% of their body mass and more than 98% of their constituent atoms {Macfarlane 1978}. Amongst vertebrates, reptiles are usually thought of as the animals most adapted or suited to such environments because of their diurnal habit, based on a need for external heat, and their ability to survive far from obvious sources of water. This impression is rein forced when one examines the composition of vertebrate faunae...