SUPPRESSED EFFECTS 43 



wild grey shade is dominant to another which produces 

 the yellow-grey shade, while, in the other, a factor which 

 is concurrent with either shade of grey is dominant to 

 a factor which is concurrent with albino ; and, as the 

 factor producing the wild grey shade must have come 

 from the albino parent, albino therefore carries a factor 

 whose effect is invisible. If we symbolize these two 

 pairs of characters by W = wild grey shade, y = yellow- 

 grey shade, C = the factor concurrent with grey, 

 irrespective of shade, and c = that concurrent with 

 albino, then the four groups in the hybrids' progeny 

 should be : 



Unfortunately the connexions between the two shades 

 of grey were not followed up in Mr. Hurst's experiments. 

 Of the seventy hybrids, only seven were bred from ; 

 and, although the yellow-grey was one of these, its 

 colour was not observed again. Among the hybrids' 

 progeny and in later generations, " a few individuals 

 appeared to have rather more yellow and less black 

 than the wild grey ; but, curiously enough, not one was 

 a true yellow-grey hke the Belgian grandparent." This 

 may perhaps be accounted for by the small number of 

 hybrids bred from or by the fact that most of their 

 progeny were killed very young. It may even be that 

 there are many factors producing different shades and 

 yellow-grey is mainly the result of several recessives. 

 At any rate, nothing more can be said meantime about 

 the factors in which yellow-grey and wild grey differ. 



