a larger and more compact body in areas of low temperature, and a less compact 

 body with longer limbs and greater surface area in hot climates. As regards coat 

 covering, one would naturally expect a thicker coat — with correspondingly greater 

 insulation ~ in colder than in warmer climates, though this may of course be affected 

 by seasonal shedding. 



These differences are well illustrated in the conformation and coat formation of 

 sheep as one goes from the northern latitudes to the equator, i.e. as the environ- 

 mental temperature increases. The Dorset Horn sheep is typical of our own tem- 

 perate area. The body is of fair size, the conformation compact, the legs short, the 

 neck stocky and the ears small. There is a thick and compact wool coat. This ani- 

 mal may be compared with the Kurdi sheep, typical of the Northern Iraq desert. Here 

 the body is still of fair size and the coat ample, as would indeed be necessary dur- 

 ing the cold seasons. But the legs are longer, the neck less stocky and the ears 

 large, — a phenomenon which is incidentally paralleled in Hamilton's work on ear 

 size in hares. The desert sheep of the tropics (for instance of Eritrea and the Sudan) 

 illustrate the extreme development of these various features. The body is far less 

 regular and compact, the legs exceptionally long, the neck elongated and the ears 

 large. Moreover, there is now a complete change in the nature of the coat, which in 

 place of wool consists of fine short hair, — a characteristic typical of sheep in all 

 hot tropical regions of low elevation. I say 'of low elevation' because at higher al- 

 titudes (and therefore at lower environmental temperatures) this generalization no 

 longer holds. The sheep of the Yeman plateau, which is at the same latitude as the 

 Sudan, are not only wooUed and otherwise comparable to those of the northern 

 deserts, but are in fact virtually earless. 



Closely comparable changes in conformation and coat thickness are found in 

 desert goats. The Angora or Maraz goat — the origin of our Mohair supplies — which 

 is found in Turkey and the extreme north of Iraq, is relatively compact, with shor- 

 tish extremities, small ears, and a copious covering of fine hair. The Persian goat, 

 still well coated, is somewhat longer limbed and longer eared, with a less compact 

 body,- characteristics which are exaggerated (particularly as regards ear size) in 

 the Syrian desert goat. Here again, however, there is a dramatic change in both 

 form and coat in the tropical regions. As with the tropical desert sheep there is a 

 marked elongation of the body and neck, the legs are characteristically lengthened, 

 and the ears are almost uncomfortably large. Moreover the thicker coat of the nor- 

 thern type is again replaced by one of fine short hair. 



Too much influence on length of leg should not, of course, be attributed to 

 direct climatic effects; apart from other reasons, animals in desert areas are charac- 

 teristically nomadic, and therefore require facilities for long and often relatively 

 rapid movement. This is perhaps best illustrated (if I may break my sequence) in the 

 length of leg of animals inhabiting northern deserts, — of which an excellent example 

 is the wild ass of the Gobi Desert. Donkeys are the most important class of equines 

 used by man in desert areas and their ability to cover long distances over waterless 

 tracts is one of their greatest assets, — not unconnected, probably, with their origin 



170 



