52 THE AMERICAN NATURALIST [Vol. XLIII 



This was the real beginning of the trotting breed of horses. 

 During the later years of the life of Hambletonian 10 and sub- 

 sequent to his death his sons were patronized by owners of 

 well-bred and speedy mares. The more successful of these 

 sons naturally received heavy stud patronage as long as they 

 remained serviceable. When the grandsons of Hambletonian 

 10. with two generations of speed-producing sires back of them 

 and out of selected female ancestry, came into service, it was 

 found that in many instances they sired faster colts than did 

 their sires or grand sire. Only in more recent years were 

 representatives of popular families used for stud purposes in 

 earlier life. 



In view of these facts, I deem it unfair to base a conclusion 

 upon a comparison of two results, one of which (13 years as 

 the average age at time of service of sires in four generations 

 back of horses in the 2.10 list) comes largely from an investiga- 

 tion of the formative period of the breed, while the other (9.43 

 years as the average age at time of service of immediate sires 

 of average horses) mainly refers to more recent conditions. 



If the figures 9.43 and 13.00 had been derived by similar 

 means their value would be unquestionable. A really fair com- 

 parison would demand the same procedure in one case as in 

 the other. Either all sires in the four generations of the thou- 

 sand horses should be used or else only the immediate sires of 

 those in the 2.10 list. 



Assuming 9.43 to be correct for the average age of the sires 

 when they produced the first one thousand horses in the Index 

 Digest, I have attempted to secure a similar figure for the 

 immediate sires of the horses in the 2..10 trotting list as pub- 

 lished in "Yearbook," Volume 22. The list published in that 

 volume contains 279 horses. In thirty cases the records failed 

 to show the horse's age. In seven cases the age of the sire is 

 not given. This leaves 242 of the 279 in the list for which the 

 ages are shown. 



Below are given two extremes and the average for 242 horses 

 regarding which there exists no uncertainty: 



