Wilson — Unsound Mendelian Developments. 413 



represented by .r, which is common to both groups. Its dominant must 

 tlierefore be X ■ 



It will be noticed that, when X has a chance of showing itself, the rabbits 

 are coloured, while, when x has a similar chance, they are albinos. The 

 difference between X and x is that X is conciin-ent witli colour-production, 

 and X with albinism. It is no unfair assumption, therefore, that, in some 

 way not disclosed, X allows or causes colour to be made, while x does not. 

 Thus, tlie factor which allows colour to be produced as in the grey is 

 dominant to that which does not allow it to be produced as in the albino. 



The factors left over to have effect in the production of some particular 

 colour are Fand //; and, since grey occurs in the group of nine, and black 

 in the group of tliree, I" must be the factor connected with grey, and y with 

 black. 



Substituting now the initial letters of the words ' colour,' ' grey,' 

 ' black,' and ' albino ' for the symbols previously used, we can write down 

 the whole ease thus : — 



And this solution agrees with the facts of the ease. The constitutions of 

 the pure individuals in each group are grey CCGG, black CCbb, grey 

 albino aaGG, and black albino aahb. One albino contains the factor for 

 greyness, while the other contains that for blackness, just as Mr. Hurst 

 fouud ; and in the first crosses the greys will behave as dominants to all, 

 just as Mr. Hurst found, while the second crosses from all possible pairs will 

 come out in agreement with experimental and other observations, thus : — 



1. Grrey x black will give 3 grey : 1 black. 



2. Grey x grey albino will give 3 grey : 1 albino. 



3. Grrey x black albino will give 9 grey : 3 black : 3 grey albino : 

 1 black albino. 



4. Black xgrey albino will give the same result. 



5. Black X black albino will give 3 black : 1 albino. 



6. Grey albino x black albino will give albinos only. 



The presence and absence theory arrives at a different result. It 

 introduces an extra factor which pushes the factor for blackness out into 

 a new position. The factors employed are — grey {G), absence of grey {g); 

 presence of colour (C), absence of colour (c) ; and black {B). The factor g 



