HEREDITY OF RACEHORSE STAMINA 55 



number the mares by two to one. The following 



figures, taken for the last ten years, show the ratios 



of horses to mares for the different ages, the mares at 



each age being represented by unity : — 



7 yrs. 

 and 

 2 yrs. 3 yrs. 4 yrs. 5 yrs. 6 yrs. upwards 



1 1-6 1-9 2-4 3-4 5 



In the following Table IV. is shown the propor- 

 tion of winning colts to fillies from three years up- 

 wards of the progeny derived from the stallions 

 numbered one to sixty in Table III. 

 TABLE IV. 



Table showing the Proportion of Winning Colts 

 TO Fillies, from Three Years Upwards, all 

 FROM THE Stallions shown in Table III. 



* St. Simon's winners prior to 1899 are not included in the calculation. 



The above figures show that factors are at work 

 which place the mares at a disadvantage as race- 

 horses after two years of age. One of these factors, 

 manifestly, is a sex limitation, in certain mares, of the 

 specific functions of the staying muscle fibre. 



A further proof of sex limitation for this character 

 is obtained by taking out, from the produce Table 

 III. of the specified sires, the ratios of horses to 



