42 Colours of Animals [CH. 



Horse. 



Chestnut recessive to bays and browns. Relations of these two domi- 

 nants to each other not clear. Hurst (158). 



Pigs. 



Several notes published by Spillman (249, 251-2). White is usually a 

 dominant to colour in domesticated races* but piebalds are frequent in F^. 

 The relation of black to red is not yet clear. The white belt, characteristic 

 of certain breeds, is, according to Spillman, due to a complementary pair of 

 factors which may be separately carried by self-blacks. He makes the 

 interesting suggestion that the appearance of the belt may be a "reversion" 

 to a condition like that of the Indian Tapir (251). 



The colour of the wild boar is dominant to the red of Tamworth and 

 segregates normally from it (252). The wild colour is presumably due to 

 an " agouti " factor like that of the rodents. 



Sheep. 



From such fragments of evidence as I can find it seems that the white 

 of ordinary sheep is not, as in the pig, a dominant to colour, but a 

 recessive. From Darwin's record (An. and Pits. n. p. 4) of the appearance 

 of all black sheep from a cross between white Southdown ewes and a 

 Spanish ram with two black spots, it may perhaps be inferred that the 

 black colour is due to complementary factors. 



Black face and white face give a speckled face in the heterozygote. 

 The dark ring round the eyes depends on a separable factor (Wood, 312). 



Fowls. 



Colours very complicated and genetics imperfectly understood. Whites 

 are of various kinds, one being dominant and at least two recessive. 

 Colour depends on complementary factors which may be borne by whites. 

 Black is an imperfect dominant to black-red. Brown-red a dominant to 

 black-red (Fig. u). Blue is a heterozygous colour of black and a splashed 

 white. The red and yellow pigments of the black-red cock may be replaced 

 by white, thus giving the Silver Duckwing, but in the hen the red of the 

 breast is not thus replaced, and the Duckwing hen differs from the black- 

 red in having the yellow of hackle and mantle replaced by white. These 

 replacements may occur as consequence of recombination in F 2 from 

 crosses between white and coloured breeds, whence it is to be inferred that 

 the replaced reds and yellows depend on a special factor. Pencilling is a 

 dominant to its absence, and various mottlings are also dominant. The 

 descent of colour is influenced in some cases by sex in ways not yet clear, 

 and in both sexes heterozygous types occur. 



The relations of the buff of Cochin (and of other breeds derived from 

 it) to other colours are not yet known. 



As regards colour of the down, the brown striped condition is dominant 

 to the pale brown down associated, for example, with Wheaten. Both 

 types of down may occur in the same breed (e.g. Indian Game), and the 

 fact seems to have no relation to the adult plumage. R.E.C. (21, 22). 



* Mr Staples-Browne has given me confirmatory evidence. 



