F. M. Durham 161 



mice without the factor for concentration are produced. These when 

 mated with blues or silver fawns throw only the dilute varieties, whereas 

 pink-eyed mice descended from unions between pink-eyed mice and 

 dark-eyed mice of the concentrated form only throw concentrated forms 

 when mated with the dilute varieties. There is a great deal of varia- 

 tion in the depth of colour of the pink-eyed mice and I think that the 

 presence or absence of the factor for concentration accounts for this. 

 Unfortunately I did not recognize this fact early enough in my experi- 

 ments to be able to give numbers in support of this view. In the case 

 of the champagne mice, however, a different variety which I called 

 " silver champagne," arose and always appeared in the F^ generation 

 from a mating between champagne and silver fawn. These silver 

 champagnes mated with dilute forms always gave dilute forms. 



When the chocolate lilac mouse is mated with the ordinary wild 

 colour or golden agouti mouse, the ^i is always golden agouti. All 

 possible forms should appear in F^. Black, chocolate, golden agouti, 

 cinnamon agouti, blue lilac, chocolate lilac, champagne, pink-eyed golden 

 agouti, pink-eyed cinnamon agouti. 



The pink-eyed agoutis, golden and cinnamon, are very much alike in 

 appearance. In fact at first and for some time I took the pink-eyed 

 cinnamon agouti to be a pale or dilute form of the pink-eyed golden 

 agouti, and owing to the small amount of pigment present, I thought 

 that the pink-eyed golden agouti must be the cinnamon variety. 

 However, the genetic behaviour of the two forms when mated with 

 chocolate showed their differences. 



The pink-eyed golden agouti gives only golden agouti when mated 

 with chocolate and the pink-eyed cinnamon agouti gives only cinnamon 

 agoutis as a result of mating with chocolate. 



The small amount of pigment present makes the microscopical 

 determination very difficult. 



Pink-eyed coloured mice are recessive to dark-eyed mice and when 

 mated inter se never throw the dark-eyed form. 



Taking all the results irrespective of colour and classifying only 

 according to eye-colour, then as a result of mating pink-eyed mice with 

 dark -eyed mice in F^ I obtained 



875 dark eye, DE, 303 pink eye, PE, observed 

 883-5 „ 294-5 „ calculated. 



From matings between heterozygous DE with PE 

 105 DE, 113 PE, observed 

 109 109 calculated. 



