50 THE MENDEL JOURNAL 



course is determined by the bodily qualities brought 

 in by the gametic factors of his parents. In other 

 words, it is determined by the germ plasm. It is a 

 congenital matter. 



In Table III. all two year old running is ignored, 

 as horses of that age are rarely asked to race over a 

 greater distance than five furlongs, and further at this 

 period of their existence the tissues, and especially 

 the dark red muscle fibres, are immature. If a horse 

 does not run after two years it is difficult to arrive at 

 his somatic composition as regards muscle fibre. 

 The same difficulty arises in connection with those 

 individuals which run after that age but do not 

 succeed in winning a race on the flat over any distance. 

 Not infrequently the interactions of nerve force and 

 muscle fibre lead to some strange and unexpected 

 results. A horse may have all the physical and 

 physiological properties of a " stayer," but be too 

 slow for racing, owing to his motor-nerve cells dis- 

 charging with insufficient force or rapidity. On the 

 contrary, he may possess nerve cells capable of dis- 

 charging in a superlative degree, but carry muscle 

 fibres which become asphyxiated before he has run, 

 at racing pace, the minimum distance of five furlongs. 

 To include these two classes would introduce a large 

 element of personal opinion, therefore they have 

 been omitted from the produce groups of the various 

 stallions. In regard to horses and geldings the slow 

 staying group is undoubtedly the more numerous, 

 but in mares the reverse condition obtains. Thus 

 though the sexes are produced in approximately 



