142 MISS MAUDE L, CLEQHORN ON THE INHERITANCE OF 



blue eyes the brown pigment is absent and the purple pigment 

 shows through the tissue forming the iris, and makes it appear 

 of a clear deep blue, when the tissue through which it is seen is 

 very delicate — and of a clear grey or pale blue when the tissvies 

 are more or less coarse. So, to trace the dominance of brown 

 eyes the real nature of the variovis kiuds of light eyes must be 

 carefully made out; it then becomes clear that the presence of the 

 hrown pigment in brown eyes makes broivn eyes dominant to blue 

 eyes in ivhich it is absent. If one parent has' very dark brown 

 eyes and the other clear blue eyes, all the children willhave dark 

 eyes, which sometimes include hazel, green or grey, but none will 

 have clear grey or blue eyes. The reason for there being no 

 blue-eyed children is apparent, for all the children inherit a 

 factor, or unit character for pigment from the dark-eyed parent, 

 but a factor lacking in j^igment from the blue-ej^ed parent — and 

 the presence of this pigment in all the children makes brown eyes 

 dominant to blue. 



To return to the colour of the cocoons the simplest explanation 

 will be found in the interaction of two simple Mendelian 

 characters. These two characters are flesh colour F, and yellow 

 colour Y, and the two pairs of unit characters involved are — 



1. Flesh colour F. Absence of flesh colour f. 



2. Yellow colour Y. Absence of yellow colour y. 



The parent moths, then, have the following constitution : — 



(1), Yellow Italian possessing the flesh colour and lacking the 

 yellow colour of the Nistri ... ... ... FFyy 



(2) Japanese white lacking both characters ... . . ffyy 



(3) Nistri lacking the flesh colour and possessing the yellow 



colour YYff 



The actual parents in the experiment were : — 



P^ the Ital.-Jap. Hyb. an F^ of a cross between the Yellow 

 Italian and White Japanese. 



P, the ISTistri. 



The Yellow Italian has a deep pinkish yellow (flesh coloured) 

 cocoon. It inherits two factors, one for the flesh colour F, anel 

 oiie for the absence of the yellow colour y, from each parent, and 

 so consists of the union of two similar pairs of factors Fy and Fy. 

 The Yellow Italian is therefore pure (homozygous) as regards the 

 colour, for the germ-cells (gametes) by the union of which it was 

 formed, each carried the same kinds of factors Fy and Fy. So 

 the gametic composition of the Yellow Italian for the colour of its 

 cocoon is represented as FFyy in Table 4, Diagrams (1) and (2). 



As the whiteness of the Japanese cocoon is due to the absence 

 of both the flesh colour of the Italian, and the yellow of the 



