112 Eye-Colours of Mice [ch. 



knowledge as to which of these colours are compatible with 

 the pink eye and which are not. 



Elaborate experiments were made by Darbishire (90) 

 to test the inheritance of these mice. The waltzers used 

 were all pink-eyed and bred true to that character. In 

 general terms the coat-colour was fawn-and-white, but no 

 detailed account of the pigments present has been published. 



Crosses were made between these waltzers and ordinary 

 albinos. The F^ generation so produced were usually, as 

 regards coat-colour, grey like wild mice, the shade being 

 sometimes darker, sometimes lighter, together with more or 

 less white. In a few families the colour was black. The 

 albino parents being of miscellaneous origin, such diversity 

 in /^l colour is what we should now expect. 



In respect of eye-colour the remarkable fact was ob- 

 served that the F^ mice were always black-eyed. \xv F^ 

 various coat-colours occurred, including a peculiar new type 

 with exceedingly dilute pigment in the hair, spoken of as 

 "lilac." Among these coat-colours the eye-colours were 

 distributed according to systems not yet ascertained. All 

 that can be clearly perceived is that the mice with agouti 

 or full black in the coat-colour (whether pied with white 

 or not) always had black eyes ; the completely white indi- 

 viduals always had pink eyes ; and lastly, the eyes of the 

 ''lilac" mice were always pink^. The facts were un- 

 fortunately presented by Darbishire in a form which makes 

 further analysis impossible. A proper investigation of this 

 series of phenomena would have greatly increased our 

 knowledge of the genetics of pigmentation. 



The important conclusion may nevertheless be con- 

 fidently drawn that at least two factors are concerned in 

 producing the black colour of the eye. Cu^not (88, p. 11), 

 as the result of his own experiments, identifies these with 

 (i) colour in the coat; (2) a factor determining the black- 

 ness of the eye, which needs the coat-colour factor as its 

 complement. This is no doubt a part of the truth, but 



* Miss Durham (116) has shown that the pink eyes of these "lilac" 

 mice and of the original pink-eyed waltzers are not wholly devoid of 

 pigment, but contain traces both in the iris and choroid visible in 

 microscopic sections. The eyes of the albino mice are absolutely without 

 pigment. 



