C. J. Bond 77 



Hurst's classification of eyes as Simplex and Duplex, and it might be 

 better to divide eyes from the colour standpoint into (a) non-anteriorly 

 pigmented and (6) anteriorly pigmented eyes, while (b) would be further 

 divided into singly pigmented (Hurst's duplex) and doubly pigmented or 

 (triplex) eyes. If the eye of the Silky Fowl be examined in the fresh 

 condition, or preferably after a few days preliminary hardening in 

 formalin, and if the anterior surface of the iris be exposed by careful 

 peripheral detachment from the scleral margin under water and if 

 further the anterior layer of black pigment cells be carefully scraped 

 away with the point of a scapel from the front of the exposed iris, an 

 underlying layer of reddish yellow pigment comes into view. This yellow 

 layer can in its turn be scraped away, leaving exposed the unpigmented 

 stroma cells and the muscular fibre cells of the deeper portions of the 

 iris, and if these be removed the posterior uveal pigment is reached. 

 The histology of this double layer of pigment cells of different colours 

 in the Triplex eye is of interest. 



The anterior black layer is made up of a dense network of ramifying 

 cells crowded with dark brown or black spherical granules, uniform in 

 size, such as we have already described as occurring in the black eyes 

 of many species of wild birds. These cells are especially numerous 

 around the capillaries on the anterior surface of the iris. The yellow or 

 red-yellow layer lies beneath this and, as in the yellow eye of other 

 breeds of fowls, is made up of two factors: (a) connective tissue cells 

 containing large numbers of yellow pigment granules (these cells are 

 less branched than the black cells and are situated around the capillaries 

 in striated muscle fibres); (6) a copious deposit of yellow pigment 

 granules in the striated muscle cells. There is a marked discontinuity 

 and absence of grading between the yellow and black pigment layers. 

 An object lesson is thus provided in the adult individual zygote of the 

 definite histological deposition of one unit character, viz, black pigment 

 over a lower grade unit character, viz. yellow pigment, and a realization 

 in the individual of the factorial composition of the gametes into epi- 

 static and hypostatic precursory factors. 



The Genetics of the "Triplex" or double/ anteriorly pigmented eye. 



Experiments have been carried out to test the behaviour of these two 

 unit characters, black and yellow pigment, in the same eye by cross 

 breeding. Five black-eyed Silky hens crossed with a gravel-eyed Old 

 English Game Bantam cock gave in the ^i generation gravel-eyed cocks 

 and mostly black over yellow-eyed hens. In the F^ generation some 



