92 ANNALS NEW YORK ACADEMY OF SCIENCES 



carried the combination for gray belly. That yellow mice may have intro- 

 duced into their composition the factor for white belly also is shown by 

 the F x yellow crosses ; also by an experiment in which one of these F x yel- 

 lows bred to black produced some gray mice with white bellies. 



I hoped to find out whether yellow mice bearing this factor for white 

 belly have themselves in consequence a white belly, but owing to the 

 great variability of yellows in this regard, I can make no positive state- 

 ments. Most of my yellow mice have a lighter belly. I have seen some 

 with a pure white belly superficially like those of the sport, but I have not 

 tested them. In some of them, the hair was yellow proximally and white 

 at the tips, suggesting possibly the presence of the ticking factor. I have 

 also had yellows whose ventral surface was as yellow as the rest of the 

 pelage. 



Two of the F x gray, gray belly, were crossed with ordinary yellows and 

 gave some gray, gray belly, descendants ; none with white bellies. 



Crosses between the Sport and Gray Mice 



As stated, the wild sports that I obtained seemed to be heterozygous, 

 since they produced both white-bellied and gray-bellied offspring. Sports 

 V and VI, for instance, gave three gray, white-bellied, and one gray, 

 gray-bellied young. Sport V crossed to a wild gray gave two gray, white- 

 bellied and two gray, gray-bellied young. Sport I crossed to a pure race 

 of extracted gray dominants gave four gray, white-bellied and one gray, 

 gray-bellied young. One of the F x grays with gray belly, crossed to an 

 extracted dominant gray, gave six grays with gray belly. 



I have produced races of gray with white belly that breed true to this 

 condition. 



Crosses between the Sport and Black Mice 



Sport III bred to a pure black female gave one gray with gray belly 

 and two grays with white belly. Sport I (or ¥ 1 ?) to black gave two grays, 

 gray belly and one gray, white belly. Sport III, bred to spotted black 

 gave four grays with white belly and one gray with gray belly. These 

 results show again that the wild sports were heterozygous. When an F x 

 gray with gray belly was bred to black there were produced three grays 

 with gray belly and one black. 



Crosses between the Sport and Chocolate Mice 



Sport I crossed with a chocolate female gave five grays with white 

 bellies. Sport V bred to chocolate gave three grays with white belly and 

 two grays with gray belly. 



