j.86 Scientific Proceedings, Royal Dublin Society. 



seems dominant to black. In the course of his experiments recorded in 

 the "Journal of the Linueau Society " for 1904, Mr. C. C. Hurst bred both 

 black and grey rabbits which bred true, and, when they were mated, tlieir 

 hybrids were grey, wliile their hybrids' progeny were greys and blacks in the 

 ratio 3 : 1 (actually 38 and 10). Thus the previous inference is confirmed, 

 and black and grey seem each the result of single factors. 



But later experiments by Professor Castle of Harvard — a statement 

 of whose work is to be found in " Science " for 1907, new series, vol. xxvi — 

 show this conclusion to be erroneous. He dealt with six colours which he 

 divided in two groups according as they were judged to be produced by 

 or without certain pigments. I'wo different pigments and a factor which 

 affected their localization were judged to be producing the following six 

 colours {B stands for black pigment, Y for yellow, and A for tlie localization 

 factor) : — 



Series I. Series II. 



Grey, B FA Black, B Y 



Blue-grey, B (dilute) Y A Blue, B (dilute) Y 



Yellow,' B (traces) Y A Tortoiseshell,^ B (traces) Y. 



Among the six colours Professor Castle found the following Meudelian 

 relations : — 



(1) Grey is dominant to blue-grey, black, and yellow. 



(2) Blue-grey is dominant to blue. 



(3) Black is dominant to blue and tortoiseshell. 



(4) Yellow is dominant to tortoiseshell. 



(5) Grey is produced by mating black with either yellow or blue-grey. 



Since it is dominant to three different colours, grey must be the result 

 of three different factors at least, and since they are intermatable, so also 

 must the other five colours. There should therefore be three pairs of factors 

 in operation, and eight different colours in all. Since blue-grey, black, and 

 yellow differ each from grey in one pair of characters, the first four groups 



in the set are determined at once, name 



Grey, 

 Blue-grey, 

 Black, 

 . Yellow, . 



■y— 



. 27 X Y Z 



. 9 X r s 



. 9 X !/ Z 



. 9 X Y Z. 



and " ; these are the English equivalents of white-bellied yelloir and sooty yellow. 



