226 MAINE AGRICULTURAL EXPERIMENT STATION. I915. 



besides the general theory of the inbreeding coefficients and the 

 practical means for their calculation, the consequences of con- 

 tinued brother X sister and parent X offspring breeding were 

 discussed. Along the same line we shall now consider the the- 

 oretical consequences of 



(a) Continued mating of first cousins, and 



(b) Continued breeding of individuals exhibiting the avun- 

 cular type of relationship, that is, uncle X niece or nephew X 

 aunt. 



Another matter which will be discussed, as it was not con- 

 sidered at all in Bulletin 215, is the measurement of the pro- 

 portionate part played in the total observed inbreeding by the 

 fact that sire and dam are related to each other, as compared 

 with inbreeding in the ancestr}' of either sire or dam alone. 



Cousin Mating. 



There are two possible sorts of first cousins, single and 

 double. In the first case one of the parents of any individual 

 is a brother (or sister) to the one of the parents of the other 

 individual in the mating. In the second case, both the parents 

 occupy this relation to the parents of the other individual in the 

 mating. 



These two sorts of first cousinship are shown in Pedigree 

 Tables I and II. 



