488 Scientific Proceedings, Royal Dublin Society. 



than one pair of characters. If we call the third dominant Z, then the 



characters carried by the first set of four groups are 



Grey, . . . . Q K Y Z 

 Black, , . . . i X !/ Z 

 Yellow, . . . . ^ X Y Z 

 Tortoiseshell, . . . \ x y Z. 



Blue- grey differs from grey in one pair of characters. Tiiere are only 

 three possible combinations which fulfil tliis condition, namely, XYz, Xi/Z, 

 and xFZ, but, as the last two are already appropriated by black and yellow, 

 the remaining one, XYz, must belong to blue-grey. 



The characters belonging to three of the groups in the second set are 

 now known, and, if we write down the four groups with the characters of 

 the three already known, we shall be able to infer tlie characters belonging 

 to the fourth : — 



Grey, . . . . Q X Y Z 



Blue-grey, . . . . 3 X Y z 



Black, . . . . 3 X y Z 

 Blue, .... 1 



By being common to three groups, X must be common to all four, and 

 the differentiating characters in the set are therefore Y and y, and Z and s. 

 The only combination left for blue to carry is Xyz. This is precisely the 

 same result as before, and again the two unfound colours belong to the 

 combinations xYs and xi/z. 



Still another example might be considered — more especially as it has 

 received a different interpretation — in which the distribution of the characters 

 is obscured by some of the factors having inseparable effects and also by the 

 effects of certain factors being suppressed by those of others. This is tlie 

 well-known example of the fowls' combs. Rose-combed fowl were mated 

 with pea-combed, and, while their hybrids had walnut-sliaped combs, their 

 hybrids' progeny had four different kinds : walnuts, roses, peas, and singles 

 in the ratio 9:3:3:1. Since tliere are four groups in the usual propor- 

 tion, there are two pairs of characters, but since the eff'ects of the factors 

 are inseparable, the set must be set down with " unknown " symbols, 

 thus : — 



Walnut, . . . . 9 X Y 



Eose, S X 1/ 



Pea, 3 X Y 



Single, . . . , 1 X y. 



