HEREDITY OF RACEHORSE STAMINA 77 



Some Hypothetical Coxsiderations. 



Reviewing all the circumstances then, it may be 

 gathered that the assumption of the dark and pale red 

 muscle fibres being represented in the germplasm of 

 the thoroughbred by two alternative unit characters 

 requires a little qualification. It would be more 

 correct to say that a number of separate entities are 

 with some regularity correlated to form a unit 

 character, for it seems fairly certain that the various 

 properties which mark off the dark fibre are in the 

 nature of additions to the pale fibre. At some time 

 far back in the phylogeny of the horse, those additions 

 no doubt arose through germinal variation, and were 

 fixed by natural selection. But, as the thoroughbred 

 is a comparatively recent creation, having arisen in 

 the 17th and early part of the 1 8th centuries from 

 crossing the Arab, Turk, Barb, and the native Gallo- 

 way, some of his ancestors brought in the phylo- 

 genetically newer staying character, and some — there 

 are good grounds for the belief that it was the hybrid 

 Turkish horse — the older character. From the incep- 

 tion of the thoroughbred to the present moment there 

 has been persistent segregation of the two types of 

 muscle. Sprinters and stayers have with constant 

 regularity made their appearance when intermediates 

 have been bred together. And this is true whether 

 we take results in the mass or analyse the offspring 

 of specific parents as I have done in Table XII. (page 

 90). The crossing of stayers and true sprinters has 

 nearly always given intermediates. 



That these intermediate forms should at times 



