WILD SHEEP OF ASIA AND AMERICA 293 



northern races mentioned below have the ears 

 smaller and more blunted than in the typical big- 

 horn, and as the same feature is found in the 

 Asiatic members of the group, it is evident that 

 an increase in ear-length has been gradually deve- 

 loped as these sheep passed from high to low lati- 

 tudes. This increase in size is, however, not solely 

 dependent upon latitude, for it is a notable fact that 

 the races with the longest ears are inhabitants of 

 desert districts, like Sonora ; and as a number of 

 other desert-dwelling animals are characterised by 

 their unusually large ears, it seems evident that the 

 reception of sound is more difficult in deserts than 

 in other parts of the world. 



By common consent all the foregoing are rightly 

 regarded as nothing more than local phases of the 

 true bighorn. The remaining members of the 

 group are distinguished by their smaller size and 

 lighter, more divergent, and sharply pointed horns 

 of the rams (pi. xxiii. fig. i), as well as by a ten- 

 dency in the ears to become shorter, blunter, and 

 more thickly haired. American naturalists regard 

 all these as specifically distinct from the typical 

 bighorn ; but the difference, although much greater 

 than between any two of the foregoing, is only one 

 of degree, and they are accordingly all classed here 

 as races of O. canadensis, or O. cervina, if that 

 name be preferred. 



The special point of interest connected with 



