THE SHEEP. 
The domestic sheep {Ovis aries) is not a natural species, 
but an association of races whose specific origin is obscure. 
Some authors regard the turf sheep of the Stone Age oi 
Europe as the ancestor of the domestic sheep, since forms 
Fig. 317.— Rocky Mountain Sheep or Big-Horn. 
like it are now liviugin the Shetland Islands and in Wales. 
It was of small size, with slender legs, and erect, short 
horns. This sheep was supplanted by a curved, large- 
horned form, the modern domestic sheep. This latter 
