The conformation of the Jack Russell Terrier follows it’s original function. Early British fox hunters used a black and tan type terrier, rather than the Fell or Welsh Terrier, whose colouring was too similar to the quarry it was hunting, namely, the fox.
Difficulty in telling the terrier from the creature it was bolting out of it’s den brought about the desire for a more white-bodied dog. In all probability the English Black and Tan Terrier was crossed with the Old English White Terrier (both now extinct) to achieve the type of coat and colouring we have today in our Jack Russell Terriers.
The Jack Russell Terrier of today is still able to perform the functions it was originally bred to do. It has longer legs which enable it to run with the hounds. It also has a flexible body that allows it to squeeze into underground dens. This along with its engaging terrier temperament allows it to be a wonderful companion and an excellent hunter.