IJ4 Hagedoorn. 



ever result in a permanent amelioration, nevertheless it is a very 

 simple matter to find the animals homozygous for H, by testmating 

 them to fade agouti (ABCDEFGh) individuals. 



The absence of H does not only make the coat have a less 

 lustrous appearance, but it also affects the colour of the eye in some 

 combinations. Thus I found that ABcDEFgh (fade chocolate) mice 

 and rabbits, have eyes which are ruby under a certain light. Chocolate 

 having H also sometimes have eyes in which a faint glimmer of red 

 can be discerned, but this is never so marked as in the hh animals. 

 In cavies the eyes seem to be less heavily pigmented than in rabbits 

 and mice, for all hh cavies have ruby eyes, as has been stated by 

 Miss SOLLAS. We have already seen that in mice the ee animals 

 have red eyes, whatever the other factors are. It can not be said 

 that ruby eyes in mice or rabbits are caused by the absence of one 

 factor, I found that all those types which lack both c and H have 

 ruby ej'es. There are, however, combinations in which c and H are 

 both present and which nevestheless give ruby-eyed individuals. Thus 

 were my abccJEFGh (dilute agouti) cavies ruby-eyed, and nearly all 

 my ABCdEFGH mice. I also found that some of the AbcDEFDH and 

 AbcDEFgH (orange and clear orange), mice were ruby-eyed. If there- 

 fore any-one wanted to study the ruby eye as a "character" he would 

 have a very difficult task and probably would find many con- 

 tradictory facts. 



The tact that in chocolate animals absence of H produces at the 

 same time a less richly coloured coat and redder eyes explains the 

 difficulty with which the breeders of chocolate rabbits are contending. 

 They have set themselves a standard of perfection, caUing for a rich 

 brown coat and brown eyes. It is of course possible occasionally to 

 find a ruby-eyed animal whose coat is rather dark, but it is an 

 obvious impossibility to produce a fixed strain combining these two 

 "characters". 



As I have already stated, the wild Mus mnscnlus are either H or h. 

 It seems to me as if in Mus decumamis, the brown rat, there exist 

 individuals lacking H. All my rats at present contain this factor, 

 but occasionally I have seen adult wild rats which were of the colour 

 which in mice would correspond to the formula ABCDEFCh. 



It is in all the different rodents at first rather difficult to distinguish 

 between those having and those lacking H. An exception is the agouti 

 cavy, which is strikingly different with or without tliis factor. In 



