592 



THE AMEBIC AN NATURALIST [Vol. XL VII 



since in generation 3 the two individuals g and h each ap- 

 pear twice, and by our rule any ancestor is only counted 



_ _ 100(16-10) nms 

 Z, - 16 - 37.5, 



since in generation 4 the individuals m and n appear four 

 times and are only counted as different ancestors once 

 each. 



TABLE III 

 Continued First-Cousin x First-Cousin Mating 



It will be seen from this table that the upper limit 

 intensity of inbreeding approached by continued cousin 

 matings is 50 per cent. In general, cousin mating is one 

 half as intense a form of inbreeding as brother X sister 

 mating, with a lag of one generation behind. That is Z 3 

 for cousin matings is one half as large as Z 2 (not Z s ) for 

 brother X sister matings. 



The curve of inbreeding for cousin matings is given in 

 Fig. 1. 



Illustration IV. The Pedigree of the Thoroughbred 

 Horse, Postumus 



Leaving now the hypothetical cases we may consider 

 some actually realized pedigrees, and measure the degree 

 of inbreeding exhibited. I have chosen as a first case of 



of 

 sin 

 ne 



