484 Scientific Proceedings, Royal Dublin Society. 



But this makes black and chocolate differ from each other in two pairs of 

 characters, while the first experiment showed them to differ in one pair only. 

 Thus black carries only one new dominant, say Z, which, since it is outside 

 the characters concerned in the first set, must also be carried by the three 

 remaining groups. The characters carried by the four groups are now 

 therefore — 



Agouti, . . . 9 Z 



Cinnamon agouti, . . 3 X 



Black, . . . . '6 X 



Chocolate, . . . . 1 x 



Since Y and Z are the characters carried by black at the top of the second 

 set, the two pairs concerned are Y and y, and Z and s, and, since the 

 characters borne by black and chocolate and the positions in the set of blue 

 and silver fawn are already known, we may write down the set as follows : — 



Black, . . . . 2 X Y Z 



Blue, . . . . Z Y z 



Chocolate, . . . . 3 cc i/ Z 



Silver fawn, . . . 1 i/ s. 



But, since it is outside the characters in the set and is carried by both black 

 and chocolate, iv must also be carried by the two remaining groups, blue and 

 silver fawn. 



It is now obvious that there are three pairs of characters and eight 

 different combinations, all of which may now be set down along with the 

 colours of such as have been identified : — 



The two unfound colours could have been found by a cross between the 

 first and the last or between any other two differing in three pairs of 

 characters, but Miss Durham found them by two separate crosses between 

 colours differing from each other in two pairs of characters. 



Agouti was mated with blue, and their hybrids' progeny consisted of 

 agoutis, dilute agoutis, blacks, and blues in the ratio 9:3:3:1. The 



