1 10 Rye-Colours [CH. 



other characteristics. In all such inquiries the first step is 

 to distinguish the critical differences which are treated as 

 units in the constitution of the germ-cells. 



In addition to these observations on man we have a 

 few indications as to the heredity of iris-colours in birds. 



The iris of the domestic breeds of fowls presents at least 

 three types of coloration. The common colour in the full 

 grown birds is a bright red, apparently due to the formation 

 of a red pigment when the period of adult life is approached, 

 the colour in earlier stages being a dull blackish green. 



Malay fowls are peculiar in having a pale, yellowish 

 white iris the "daw-eye" of fanciers which behaves as a 

 recessive to the red iris. This eye may be found in birds 

 of various colours and probably it always indicates an 

 admixture of Malay blood*. I have seen, for instance, a 

 daw-eye in a White Leghorn of a good strain. Here it 

 undoubtedly cropped out as a recessive character among the 

 normal red-eyed birds, and I happen to know that White 

 Malays were used by a prominent White Leghorn breeder 

 to increase the size of his strain. 



Another peculiar type is seen in the nearly black iris 

 of Andalusians and Silkies. In Andalusians we have found 

 this eye imperfectly dominant to the red. The case of the 

 Silkies is much more complex and the inheritance is dis- 

 turbed by sex in the manner hereafter to be described. 



In the Little Owl (Athene noctua), Giglioli has described 

 the occurrence of a remarkable variation in eye-colour which 

 is evidently an example of the appearance of a recessive in 

 the wild state. The irides of the normal birds are yellow, 

 but in the variety, of which several specimens were found 

 in one district, the irides were black. The circumstances 

 of the discovery which are related by Giglioli in detail t 

 leave little doubt that the condition was recessive. It is a 

 curious fact that, in all the aberrant individuals found, the 

 distribution of the brown markings on the feathers also 

 differed from that of the type. So distinct was the variety 

 from the ordinary A. noctua that a new specific name was 

 suggested for it until the fact that it could be bred from the 

 type was established. 



* Sir J. Bowring (Philippine Islands, 1859, p. 151) says that "white eyes" 

 are preferred in fighting cocks. Probably these are the origin of our Malays, 

 t Giglioli, Ibis, 1903, p. i. 



