66 PROCEEDINGS OF THE AMERICAN ACADEMY. 



which Schlumberger ('94) figures and describes an ancient Japanese 

 netzuke, or charm, carved in wood, and representing with great minute- 

 ness an entire family of dancing mice. The fatlier and the mother, as 

 well as four of the young, are spotted black- white, while of the four 

 other young, two are entirely white and two entirely black. The two 

 white young, as well as their black-white mother, have pink eyes ; all 

 the others have black eyes. The dancing character in mice of this 

 variety is heritable, and, as pointed out by Castle ( : 03*^, p. 225), is 

 transmitted quite independently of color characters. 



Although the actual origin of the various breeds of mice is thus 

 practically unknown, certain of the writer's experiments seem to throw 

 light upon the method by which they may have arisen. For example, 

 albino mice of unknown ancestry were in his experiments bred to gray 

 house mice, and in the first generation only gray young were obtained, 

 indistinguishable in outward appearance from their gray parent. Sub- 

 sequently these gray offspring were bred intnr se, and also back crossed 

 with the albino stock. From both of these crosses there resulted, in 

 addition to animals of the gray type, an occasional black individual, and 

 two such black mice, when mated, produced only black young (or, if 

 they contained albinism i-ecessive, they produced albino as well as black 

 offspring, in the Mendelian ratio, 1 : 3). It may be that in this case a 

 segregation of the pigment elements has taken place in such a way 

 that the yellow element has disappeared from certain individuals, and 

 this segregation has been favored in some way by the cross made. On 

 the other hand, it is not improbable that in this particular case the black 

 character may have been transmitted directly through the albino grand- 

 parent without a segration of the compound gray character. This view 

 will be explained in detail further on. The brown, or chocolate, ele- 

 ment is present in these black mice, but is not evident to the naked 

 eye except at such times as the regular moult of the pelage takes place, 

 when the new hair is distinctly tinged with brown. 



From these black mice of /lonse-moitse derivation the writer has been 

 unable, by crossing with the same albino stock, to obtain a further seg- 

 regation of the pigments, but it would seem plausible to suppose that 

 chocolate and yellow might yet be obtained from this stock by such a 

 method. In the case of a black-white stock, however, further segre- 

 gation was obtained. The black-whites used were purchased of a dealer 

 by Professor Castle, under the name of Japanese mice, though they were 

 not of the dancing variety. These mice, when bred to the same stock of 

 albinos that was used in the house-mouse crosses, gave both gray young 



