COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 3! 



on the hypothesis of alternative dominance between agouti and black- 

 red, the young should be in the proportions, i agouti to 3 black-red to 4 

 albino. The numbers observed are 2 agouti to 3 black-red to 5 albino 

 too few to be conclusive, but favoring the former hypothesis. On the 

 whole it seems highly probable that agouti as a rule dominates over 

 all other pigment combinations, but in the case of exceptional animals 

 like ? 2020, page 27, black or black-red gametes may be formed which 

 have a potency equal to that of agouti. This is an indication of indi- 

 vidual prepotency like that discussed further on, under the heading, 

 " Prepotency and Dominance." 



Agouti synthetically produced. An occasional animal with an ex- 

 cellent agouti coat may result from mating a red with a black individual. 

 One such animal, $ 1178, tested as to the character of its gametes, ap- 

 parently forms pure red and pure black gametes in approximately equal 

 numbers, for mated with red females he has produced 3 red, 2 black, 

 and i agouti young. His red gametes uniting with those furnished by 

 the red females should produce red offspring, while his black gametes 

 forming similar unions should produce either black or agouti young. 

 Hence the result observed is exactly what we should expect, on the 

 hypothesis that black and red have formed merely a temporary, not a 

 permanent union in the agouti parent, and that the gametes formed by 

 it contain either red or black, but not the two united in the agouti com- 

 bination. What conditions, if any, can bring about a permanent union 

 between segregated red and black my experiments do not as yet indicate. 



THE BLACK TYPE. 



My original black animals were obtained from Miss Soule. Bred 

 inter se they produce only black offspring, though a few red hairs 

 may usually be found by careful search somewhere on the body. The 

 relation of black to agouti has already been discussed, so that we 

 may pass immediately to its relations with red and with albinism. 



Black X red. The young produced by this cross have ordinarily 

 a black coat, but of a reddish shade, as if the pigmentation of the black 

 parent had been diluted with that of the red one ; in other words, the 

 characters of both parents show their influence in the offspring, which 

 are not intermediate, only because black pigment is so much more 

 opaque than red that the latter is scarcely visible. In other cases the 

 weakening of the black pigmentation is seen in a restriction of the 

 black pigmented areas, which then fall into the series of pigmented 

 patches described on page 9, while red, or red and white together, fill 

 up the intervening spaces. This results in the production of a black- 

 red or black-red-white spotted animal. Or, thirdly, and less often 

 still, the black and red may have the characteristic distribution which 

 produces the agouti coat. 



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