ALLEN. — THE HEREDITY OF COAT COLOR IN MICE. 123 



D + D = gray " species," 

 DR + DR = bhick-wliite, 

 4 DR'D = Fi, mostly with white flecks. 



This generation, Fi, interbred, should give gametic unions as follows : 



DR+ D 

 DR + D 



DR + 2DR-D + D = theoretical classes, 

 77 : lo3 : 25 = observed numbers, 

 58.75 : 117.5 : 58.75 := calculated numbers. 



Crampe obtained the three theoretical classes : plainly spotted (DR), 

 hardly spotted (DR*D), and unspotted (D). These classes occurred 

 in something like the anticipated proportions, though it is clear that 

 there were more spotted rats than expected. Moreover, as his first 

 cross (Fi) showed, the union of DR and D does not always give spotted 

 animals, and this fact might serve to reduce still further the class D, 

 which is less than 50 per cent of what it was expected to be. These 

 facts may indicate incomplete segregation of the two characters, which, 

 indeed, differ only in degree. 



In general, however, it is clear thai in mice and rats the cross of a 

 wholly pigmented variety with one having partial pigmentation serves to 

 reduce the extent of the white areas in tlie offspring, so that the latter 

 may either show very slight traces of albinism at the places where albin- 

 ism is most apt to occur, or they may show no white at all. 



3. Summary on heredity of partial alhinism. To sum up, partial 

 albinism among mammals which normally are wholly pigmented occurs in 

 certain definite places in the shape of wliite })atches or breaks between 

 pigmented areas. These areas, in suffering reduction, become diminished 

 toward certain centres, of which there are ten arranged symmetrically, 

 five on either side of the longitudinal axis. 



According as the pigment patches are little or more reduced, or dis- 

 appear entirely, various degrees of partial albinism may be recognized. 

 The extreme on the one hand is that condition in which albinism occurs 

 at the extremities of the appendages, or as small flecks at the points 

 where two adjacent pigment patches had just failed to meet. The op- 

 posite extreme is that condition wherein pigment production is found 

 only in the eye, and even here a certain amount of reduction may take 

 place in the coloring matter. 



