as fast movers and their remarkable ability to make good their water deficit by drink- 

 ing at one time quantities which — weight for weight — would be impossible to man. 



Reliance on a precarious rainfall does, however, involve the need for some 

 form of adaptation which will furnish nomadic stock with a mobile reserve of food. 

 Vihile in the camel this is located in the hump, in the sheep it is located in the tail. 

 The exact form of the tail varies with different types of sheep. In sheep inhabiting 

 the northern deserts it usually consists of twin lobes, the upper surfaces of which 

 form a continuation of the woolly coat; the under surface being bare of wool. In 

 tropical sheep the tail is long, rather than wide and lobed, but is still capable of 

 storing large quantities of fat. The tail of the fat- tailed sheep may, iii the lush 

 period, attain a weight of 151b. or more; in the lean period it will shrink to an 

 empty bag or 'rope' of small proportions. It would not, I think, be out of place to 

 draw attention to the fact that the existence of a f at - tail is in no way inimical to 

 high productivity, as shown by the fine udder development and good mutton confor- 

 mation of many desert sheep. 



I have attempted in this paper to describe some of the more typical examples 

 of the adaptations of domesticated animals inhabiting desert areas. I have done 

 this with a two -fold object. First, I was anxious to stimulate interest in a field 

 which has in the past been much neglected by zoologists and physiologists, and 

 which not only merits increased attention on account of its economic importance but 

 furnishes a mass of unsolved but intriguing problems. We are, for instance, still un- 

 aware of the factors influencing tolerance to wide variations in environmental tem- 

 perature, apart from specific tolerances to heat and cold. And even in regard to the 

 latter, substantial progress has only been made with cattle, and little or no work 

 has been done on camels, fat -tailed sheep, goats and donkeys. We know little of 

 the mechanism causing local fat deposition, or of the reasons for the wide varia- 

 tions in tail and rump pattern. These and many other problems provide wide scope 

 for the research worker. 



But my second reason for presenting the paper is that it justified, in my view, 

 an extremely cautious approach to any proposals (and many have been made) to in- 

 troduce into desert and semi- arid areas types of livestock which may in their own 

 environment be more productive but which are unsuited either to the climate, the 

 vegetation or the inevitable nomadic life of desert animals. I have indeed tried to 

 show that the existing desert animals are themselves capable of quite outstanding 

 production in spite of their harsh environment. If, as I firmly believe, such animals 

 are destined to continue to play an essential role in the utilization of deserts, it 

 will not be by their replacement by — or even their inter- breeding with — so- called 

 'improved' livestock. Rather must we look for improvement by the better selection 

 among the indigenous animals themselves and by the partial alleviation of the desert 

 environment, — through improvements in water supplies for stock in grazing areas, 

 through the increased practice of semi - nomadism, and - where this is impracticable - 

 through efforts to conserve fodder as an external reserve to reduce the demands on 

 the internal reserves of the animal itself. By such means — and only by such means - 

 can we hope not only to maintain but to increase the contribution of domesticated 

 animals to the desert economy. 



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