IV] Pied Varieties 85 



pattern depended on the existence of a dominant. So also, 

 exactly as in the case of dilution and saturation, an albino 

 may carry either the whole-colour factor, or its absence. 

 Consequently when a Dutch rabbit is crossed with an 

 albino bearing self-colour, F^ is self-colour and F^ gives 

 9 self-colour : 3 Dutch : 4 albinos. 



In rats there is a type of colouring which rather closely 

 corresponds to the Dutch of rabbits. This has a **hood" 

 of colour over the back of the head and shoulders continued 

 down the back in a stripe which may either be entire or 

 broken into spots. This behaves towards the self-colour 

 just as does the Dutch in the rabbit ; and just as in the 

 rabbit the heterozygote between the self-pattern and this 

 hooded type always has some white. Crampe (^'^, a) 

 observed this fact before the days of Mendelian analysis. 

 He noticed that when a wild grey rat was crossed with an 

 albino, /^i, as we call it, might be a real self-colour, or might 

 have some white; but that subsequently hooded rats only 

 occurred as offspring of those which had some white. Such 

 rats, which are nearly whole-colour but have a little white, 

 are known in the fancy as the "Irish" type. Experiments 

 made by Doncaster and also by Mudge indicate that these 

 may be again divided into two subordinate classes, distin- 

 guished by the amount and distribution of the white, and 

 there is some evidence to show that these two types of 

 Irish rats have distinct gametic compositions. 



Though the Dutch rabbit and the hooded rat are each 

 such clearly recognizable types, yet within these types there 

 is great fluctuation, and it is practically certain that the 

 fanciers ideal Dutch-pattern rabbit, with the demarcation 

 between the colour and the white passing in a sharp trans- 

 verse line across the middle of the animal, does not exist as 

 a gametic entity. Such individuals of course come into 

 existence from time to time, but selection will not fix their 

 type. As Castle and MacCurdy (183) have shown in the 

 case of rats, selection may nevertheless to a considerable 

 extent be effective in producing hooded types with more 

 colour, and with less colour, which are evidently gametic 

 possibilities. 



In mice no pied type exists which is quite so definite 

 as the Dutch pattern of rabbits or the hooded type of rats, 



