100 Mr. G. P. Mudge. On the Hereditary — [May 8, 
The different types of rats will therefore be symbolically represented as 
follows :— 
Wild self-grey rat...... CGBSP. 
Piebald sh hpi eee CGBsP. 
Wild self-black rat .... CgBSP. 
Piebald Pe ee ae bsie 
A lbintostiabee. oe ertee ce cGBSP, cGBsP, cgBSp, cGbSp, ceGbSP, 
ceBSP, cGbsP,.cgBsP, cGBSp. 
By various combinations of these forms the number of possible albinoes can 
be increased. Thus, if cgBSP x cGBSp, a form cGegBSPp will result. 
It is very doubtful whether an albino not carrying at least one positive 
colour and one positive pattern member of each allelomorphic pair, exists. 
In accordance with the indications given by Miss Durham’s work (17), I 
shall assume that the albino carries the chromogen determiners (G and aD 
and not the ferment = tyrosinase = colour producer (C). 
In applying this “scheme” to my results, it will be necessary to assume 
that every gamete must carry one member of each allelomorphic pair. 
C. THE “IRISH” CHARACTER = CRAMPE’S Cr 6.* 
The form known in the “ fancy ” as the “Irish” rat is a nearly wholly black 
individual with patches of white on the ventral surface. With regard to its 
visible zygotic characters there are apparently two types which Doncaster (15) 
has proposed to call the “Irish” @ and the “ Irish” 6. With this subdivision 
of the “ Irish ” type (Cr 6) I am inclined to agree, and certainly for purposes 
of description it is a very necessary one. 
Doncaster’s definition of the zygotic characters of the “%” form is, however, 
unsatisfactory, because it is not sufficiently precise. According to him this 
form has more white on the ventral surface than the “a” form. My 
experience suggests that this is not the chief difference, and that we should 
define the “ Irish” } as being the form with more or less ventral white and 
with carpal and metatarsal white bands. The “Irish” @ possesses the ventral 
white alone and always very little of it, but has no carpal or meta- 
tarsal bands; the ventral white is usually merely a fleck on the chest or 
abdomen. Some of my “ Irish” 6 forms in respect of the excessive reduction 
of the ventral white approach the a form, but are at once distinguished by 
the presence of the white carpal and metatarsal bands. 
* The symbols Cr 1—Cr 7, which are used in this paper, indicate the seven varieties 
into which Crampe divided rats. These varieties are described on p. 119, and also by 
Bateson (5), and by Doncaster (15). 
