140 On the Inheritance of Colour in Pigeons 



white and so, when meeting with colour in the silver, reconstitutes the 

 original blue. In these experiments one case is met with (Exp. 63) 

 where the white is heterozygous in Bl., and so both blues and silvers 

 are produced from the mating of a silver with a white, and no doubt 

 further seai'ch would have revealed a white from which the factor was 

 absent. 



In these experiments both blue and silver chequers occurred, the 

 blues being chequered with black, and the silvers with dun. Chequering 

 is dominant to its absence. As will be seen it was introduced by the 

 whites used. Whites can be homozygous for the presence or absence 

 of this factor, or hetei'ozygous respecting it. The degree of chequering 

 varied considerably, and, in the case of the blues, a few of the darker 

 birds were with difficulty distinguished from the " reversionary blues " 

 of the Barb-Fantail matings. 



From these matings coloured birds having a certain amount of 

 white in their plumage were also obtained. The amount of white 

 varied very considerably, and the birds can be roughly classified as 

 follows : 



(a) Coloured birds with very few white feathers, i.e. considerably 

 less than in a typical C. livia. These birds have not been bred from, 

 and the significance of the few white feathers is not apparent. The 

 presence of a very few white feathers does not necessarily imply that 

 the bird is heterozygous, for I have already shown in my first report 

 that a blue with very few white feathers (No. 19 raised in Exp. 5) 

 when mated to a white (Exp. 13) did not produce any white offspring. 



(b) Typical C. livia. These birds were obtained in F„ from the 

 cross between Irish Rock Dove and white. 



(c) Coloured birds with several white feathers. When bred together 

 these have produced whites, and they are comparable with the mottled 

 birds produced in the Barb-Fantail experiments. White feathers were 

 found both on chequered and non-chequered birds. 



Lastly recessive whites were produced. No coloured feathers were 

 seen on the plumage of any white, with the single exception of one 

 bird raised in Exp. 66. A pair of whites, which were being kept for 

 further use, were allowed to mate up in an aviary containing several 

 other birds. These produced one white bird. Beyond this no pairing 

 of whites together has been made. In the Barb-Fantail experiments 

 it was shown that whites bred true, and there is no reason to believe 

 that those I'aised in these crosses would behave otherwise. 



