ALLEN. — THE HEREDITY OF COAT COLOR IN MICE. 125 



j)igment9, and (3) chocolate mice, containing the chocohite alone. Yel- 

 low mice in whose pelage is only the yellow pigment are a well-known 

 type, but the writer was unable to obtain any thorough segregation from 

 his other stocks. To avoid confusion, these types are here referred to 

 by the terms used in Rateson's paper (: 03'' ) on the types of fancy mice 

 and rats. The hairs of the mice bred by the present writer have been 

 examined with the microscope and the pigment elements found to be as 

 stated by Miss Durham. 



Wild gray house mice breed true to that color, so far as observed. 

 The writer bred a considerable number from a pair captured in Cam- 

 bridge, and four generations of inbreeding failed to produce any but gray 

 animals. 



Four house mice were bred to albinos obtained of a Boston dealer, and 

 by reciprocal crosses G7 young were produced, all of which were gray. 

 Among these was a litter of three of a very light gray, but they unfor- 

 tunately died while only a fortniglit or so old. Subsequently the same 

 parents produced normal gray young only. 



The gray heterozygotes obtained from this cross were interbred, and 

 produced, in addition to the expected albinos (extracted recessives), a 

 number of pigmented animals, 40 in all, which with a single exception 

 were gray like their parents. The exception was a mouse entirely black. 

 Here evidently was a case of segregation, the yellow pigment being 

 entirely lacking. Although this individual appeared coal black, the 

 presence of the chocolate pigment was manifest at times when the pelage 

 was moulted, the new hair appearing brownish. Bateson states that he 

 has not seen any black mouse whose hair did not contain also the choco- 

 late pigment. To account for the presence of this black mouse it may 

 be assumed that among the gametes of both its hybrid gray parents there 

 were present some which lacked the yellow pigment character. Two 

 such gametes must have united to produce the black individual. The 

 black cliaracter was probably transmitted through the albinos used, for, 

 as will be shown farther on, this stock seemed regularly to produce about 

 25 per cent of gametes bearing the black pigment character, the remainder 

 having the gray character. In the formation of gametes, therefore, the 

 gray heterozygotes must have produced some sex cells which lacked the 

 yellow pigment character. It is conceivable that this result may have 

 been brought about by a resolution of the gray character in such a way 

 that yellow and chocolate passed into one gamete, black and chocolate 

 into another. A part of the gray heterozygotes of generation Fj were 

 back-crossed with the albino parent, and of the 31 pigmented animals so 



