I have spent less time in the arid zone in the last few years than I did during the 1960's, 1970's and early 1980's. This results from a progression through age and a career structure which gradually shifted the emphasis of my work from being essentially field-oriented to essentially office-hound. When, therefore, I was asked by John Cloudsley-Thompson to undertake the writing of this hook I hesitated for two reasons. One reason was that, although I now had access to good library facilities and kept up with the literature on the arid zones and their fauna, I was not sure that a sedentary and pleasant life in a temperate highland island in tropieal Africa would provide a mental attitude suitable to writing a hook which related to areas where life is usually nomadie and often extremely disagreeable. The other reason was that I was uncertain whether I could devote the time necessary to researehing and writing the hook on top of my professional (which now specifical ly excluded research in the arid zones and on camels) and social (new-found and time-consuming) commitments. In the event I accepted and the fates were kind to me. By some peculiar combination of circumstances I was given the opportunity to spend a considerable part of the first half of 1988 in some of the driest areas of the globe. I had already visited all of the locations used for the construction of Fig. 2.

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1 Introduction.- 2 Deserts and the Desert Environment.- 2.1 Climate.- 2.2 Desert Types and Locations.- 2.3 Life in Deserts.- 3 Temperature and Heat Relations.- 3.1 Introduction.- 3.2 Bradymetaboly in the Dromedary.- 3.3 Domesticated Small Ruminants.- 3.3.1 Sheep.- 3.3.2 Goats.- 3.4 Wild Ruminants.- 3.4.1 Oryx and Eland.- 3.4.2 Springbok.- 3.4.3 Dorcas Gazelle.- 3.4.4 Grant's Gazelle and Thomson's Gazelle.- 3.4.5 Dik-dik.- 3.4.6 Other Species.- 3.5 Independence of Brain and Body Temperatures and Counter-current Cooling.- 3.6 Pelage Characteristics.- 4 Water Balance and Kidney Function.- 4.1 Introduction.- 4.2 Water Requirements.- 4.2.1 Sources of Water.- 4.2.2 Dehydration and Rehydration.- 4.2.3 Effects of Dehydration on Appetite.- 4.3 Water Turnover.- 4.4 Water Loss.- 4.4.1 Respiratory Evaporation.- 4.4.2 Cutaneous Evaporation.- 4.4.3 Faeces.- 4.4.4 Urine and Kidney Function.- 4.4.5 Lactation.- 5 Nutrition.- 5.1 Introduction.- 5.2 Structure and Function of the Digestive System of the Camelidae.- 5.2.1 The Buccal Cavity.- 5.2.2 Pharynx and Oesophagus.- 5.2.3 Stomach.- 5.2.4 Intestines.- 5.2.5 Liver, Pancreas and Spleen.- 5.3 Nutritional Physiology of Camelids.- 5.3.1 Motility.- 5.3.2 Movement of Digesta.- 5.3.3 Retention Time.- 5.3.4 Rumination.- 5.3.5 Rumen Chemistry.- 5.4 Domestic Small Ruminants.- 5.5 Wild Ruminants.- References.