So far as is known, no direct investigations have been made to test how far inbreeding may be carried in the _Equidae_; but, on the other hand, the breeding of race-horses may perhaps be looked upon as a gigantic experiment in this direction. Our English thoroughbreds can be traced back to a few imported sires--the Byerly Turk, imported in 1689; the Darley Arabian, in 1710; and the Godolphin Arabian, in 1730. Since then, by careful breeding and nutrition, they have increased on an average some eight or nine inches in height. There is, however, a widely spread impression that at present there is a marked deterioration in the staying power and in the general ‘fitness’ of the racer. The falling off is further shown by a fact commented on by Sir Walter Gilbey--viz., “the smallness of the percentage of even tolerably successful horses out of a prodigious number bred at an enormous outlay.” In support of this he quotes a sentence from the _Times_ (December 27, 1897), referring to a sale in which thirty-two yearlings had been sold for 51,250 guineas: “These thirty-two yearlings” (said the _Times_) “are represented by two winners of five races, Florio Rubattino and La Reine, who have contributed about 2,000_l._ to the total cost; and there is not, so far as can be known, a single one of the thirty others with any prospect of making a race-horse.” If, then, it is true that the English race-horse is on the down grade, what steps should be taken to arrest this descent? Sir Everett Millais restored a pack of basset hounds by crossing them with a bloodhound, the original forefather of bassets. The resulting pups were bassets in form, but not quite bassets in color; when, however, these cross-breeds were mated with bassets the majority of the pups turned out to be perfect bassets both in shape and coloration. This indicates that one way to rejuvenate the race-horse would be to have recourse to a new importation of the best Arab mares that the plains of Arabia can produce. Breeders hesitate to adopt this course, because their present breed is not only larger but, over very short distances, fleeter than its forefathers. The shortening of the course in recent years is probably a further sign of the degeneracy of our present racers. Were new blood introduced and more three- or four-mile races instituted, we should doubtless soon have a return to the champion form of bygone days. Another method would be to import some of the racers of Australia or New Zealand and cross them with the home product. Different surroundings, food, etc., soon influence the constitution, and this being so, it would be advisable to select those horses of pure descent which have been longest subjected to these altered conditions. Thus the chance of reversion occurring would be increased.