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IRE AMERICAN NATURALIST [Vol. L 



In an earlier paper (1913), I have reported a cross sim- 

 ilar to the one here recorded and have shown that three 

 pairs of alternative mendelizing factors are involved. 

 These are : 



A — gray-bellied agouti. a — non-agouti. 



B — black pigment. b — no black pigment. 



D — intense pigmentation, d — dilute pigmentation. 



The gray-bellied agouti parent was homozygous for 

 the factors for gray-bellied agouti, black and intensity 

 being AABBDD in zygotic formula. The dilute brown 

 parent was homozygous for the hypostatic conditions, 

 non-agouti, no black pigment, and dilute pigmentation, 

 and was, therefore, aabbdd in formula. 



The Fj gray-bellied agoutis would of course be hetero- 

 zygous for all three pairs of factors and would be AaBbDd 

 in formula. When such ¥ 1 hybrids are crossed together, 

 eight color classes of young are expected in a 27, 9, 9, 9, 

 3, 3, 3, 1 ratio. As will be seen from Table II, this result 

 was approximated with the addition of a ninth and un- 

 expected color variety, the white-bellied agouti. 



TABLE II 



