594 



THE AMEBIC AN NATURALIST [Vol. XL VII 



100( 4 - 4) 

 4 



100(8 - 8) 



Z 4 = \ = 15.625, 



100(82 - 

 32 



From these results it is possible to make a precise 

 statement as to how much Postumus was inbred. In the 

 five ancestral generations, to which the pedigree extends, 

 he was inbred to an extent (15.6 per cent.) which repre- 

 sents approximately three fifths of the intensity of in- 

 breeding involved in once mating first cousins. In other 

 words, if in the first ancestral generation, a mating of 

 first cousins had occurred, and there had been no other 

 mating of relatives whatever, Postumus would in that 

 event have been nearly twice as much inbred as he actu- 

 ally was. 



In the first three ancestral generations Postumus was 

 not at all inbred, and in the first four only 6.25 per cent., 

 an intensity equal to about one fourth of that involved in 

 once mating parent X offspring. 



These figures are definite pedigree constants for the 

 horse Postumus, which are directly comparable with 

 similar constants for other animals. 



Illustration V. The Pedigree of the Brown Swiss 

 Bull, Saxton (2668) 



We may next consider a more complex case, in which 

 the intensity of inbreeding is greater, and in which the 

 calculation of the coefficients is not so simple a matter be- 

 cause of the length of the pedigree. On this account the 

 method of computation will be illustrated in detail. As 

 before the "X" with an animal's name indicates that it 

 has appeared at least once before in the lower ancestral 

 generations and can not therefore be counted again. The 

 pedigree of Saxton, a bull of the Brown-Swiss breed of 

 cattle, is given as Pedigree Tables VII-XVI. 



