46 A. Comfort 



were under 13 years old lived slightly longer (17-39 ±0-36) 

 than those whose parents were over 13 (16-45 ± 0*48; t ^ 

 1-4, 0-2 > P > 0-1), and the difference was greater in the 

 extreme segments of these groups (dam and sire ^ 9, 17 • 91 ± 

 0-47; ^ 16, 15-71 iO-83; t ^ 2-3, 002>P > 0-01). This 

 difference is much smaller than that described by Vitt from 

 maternal age alone, and is of the order of the difference 

 between cohorts. 



In view of this result, the five additional cohorts (sample B) 

 were extracted and scored for parental age, with the results 

 shown in Table III. The differences found in the 1875-80 

 sample were not repeated here. The longest-lived group were 

 the progeny of parents of 16 years and over, but the standard 

 error was very large (17-26 i 1-90); the 220 animals which 

 were the progeny of two young parents had numerically the 

 shortest lifespans (16-51 i • 52) ; none of the differences was 

 significant, and all were in the reverse direction to those in the 

 1875-80 sample. 



The mean expectations of life were also calculated for the 

 foals sired early and late in life by three selected stallions: 

 Hermit, by Newminster (1864-1890); Galopin, by Vedette 

 (1872-1899); and Hampton, by Lord Clifden (1872-1897), for 

 comparison with Vitt's analysis of the progeny of Swynford. 

 These three stallions produced in their lifetime 141, 119 and 

 159 fillies which returned to stud. Forty-six, 13 and six of 

 these came from the cohorts already scored, the remaining 347 

 being new lives. The combined curve of survival for all 

 Hermit, Galopin and Hampton mares coincided closely with 

 that for the original six cohorts ; their mean expectation of life 

 at 4 years was 16-50 ±0-39 years. The 121 mares got during 

 or after their sire's 20th year had a slightly, but not a signi- 

 ficantly, higher expectation than the global mean (16-65 db 

 0-57) (Table III; Fig. 3). Only 41 mares were got by the 

 three selected stallions in or after their 16th year upon dams 

 16 years old or more; these had a mean expectation of life of 

 16-29 ±0-94 years. By combining these mares with the 



