108 Hagedoorn. 



Two pairs of thpse whitcbellied rats of the spcond ^PtiPration gave: 

 one pair 8 whitebellied and 3 darkbeilied. the other pair g'ave ouly 

 wiiitebellied young, 11 in all. of which one waltzer. 



We can find records of only one mating between two darkbellied 

 yellows and this produced 8 young, all darkbellied yellow. 



Silver animals may or may not contain this factor B which in 

 agouti and yellow rats produces a white belly. Its presence or absence 

 makes no difforence in the colour of the belly or any part of the coat. 



Onf pair of silvers bred intor se produced 8 silvers, and 3 yellows, 

 (if wliidi one darkbellied. 



Mating the original silver with a whitebellied yellow produced 

 7 whitebellied yellows and 6 silvers. 



A darkbellied yellow mated to a silver produced 1 white bellied 

 yellows and 5 silvers, the factor B having be^n introduced by the 

 silver parnnt. There is one litter of four young from a silver female 

 and a darkbellied agouti. 2 young are black, and 2 whitebellied agouti. 

 The agouti parent must have been homozygous for one or both of the 

 factors, which the yellows have less than the blacks and agoutis, and 

 the silver parent has introduced the faetoi' B, making the agouti young 

 whitebellied. 



One pair ^f two iilarks must have been heterozygous both for 

 factor A, for ß and foi' either C. D or both. Their offspring consisted 

 of 10 blacks, 1 darkbellied agouti, 1 whitebellied agouti, 1 silver and 



I whitebellied yellow. 



The original pair of darkbellied agoutis, born in the same litters 

 with our first yellows and waltzers gave 14 darkbellied agouti and 

 5 darkbellied yellow. 



»liite tailtip. 



Two litters from a ])air of two whitebellied airoutis contained 



II whitebellied agouti and 4 darkbellied agouti, one of the former having 

 a white tip. This is the second time in which animals with white tips 

 were produced, and in this mating again it is clearly seen that two 

 genes are concerned. In almost all instances however, where such new 

 characters originated by a simultaneous lack of two genes, there was, 

 later shown to be only a difference in one gene between animals with 

 the novel character and related normals. In this mating both animals 

 must have been heterozygous for E and F. being EeFf. Later work 

 with this character must have consisted in crossing ef animals to 



