MORGAN, COAT COLORS IN MICE 89 



me from Iowa some mice caught in the fields, which were supposed to be 

 Peromyscus because of the white belly. These were the same sports that I 

 had obtained in Woods Hole. I have also found in the collection of house 

 mice at the American Museum of Natural History in New York a few 

 skins with the characteristic white belly. The sport must be, therefore, 

 wide-spread. Since it appears to be found less often in the cities than in 

 the country, it may possibly be a variety that occurs most often in the 

 fields, or the conditions there may be more favorable for the appearance 

 of the sport; and since, as will be shown below, it is a dominant type, it 

 may in time spread and supplant the ordinary gray-bellied house mouse. 

 Cuenot has recorded the appearance of this or of a similar sport in his 

 domesticated races, but whether it arose there as a sport or was already 

 present in some of the stock he used (in the yellow, for example) cannot 

 be determined from his data. The sport resembles in all respects the 

 house mouse except in color. The hair under the chin, neck and belly is 

 pure white, the white extending to the flanks. Each hair has a dark base, 

 i. e., it is "ticked" and differs in this respect from the white spots seen in 

 varieties of domesticated mice. This difference shows that the new sport 

 has not arisen from escaped spotted mice. A narrow yellow band extends 

 along the flanks between the fore and hind legs. The yellow band is 

 strongly marked off from the white below, but less so from the gray of 

 the sides above. The rest of the body is gray, but in most of my speci- 

 mens, the gray is somewhat darker than that of the ordinary gray house 

 mouse. Under the microscope, the hairs of the yellow flank are seen to 

 have a yellow tip and a black base. The gray back also contains some 

 hairs with a yellow tip and a black base, also hairs entirely black, while 

 other hairs have a brown tip and a yellow mid-band. The white hairs of 

 the belly have a white tip and a black base, while the ventral gray hairs 

 of the gray-bellied mice have black extending nearly to the tip. The tip is 

 yellow or nearly colorless. Even here, however, one meets with hairs that 

 are yellow all the way to the base. 



There are no intergrades between the white-bellied and the gray-bellied 

 mice. There has never been any doubt concerning the nature of the 

 several hundreds of mice descended from the wild sport that I have ob- 

 tained. On the other hand, it should be stated that there is a wide range 

 of fluctuation of the color of the ventral surface in the house mouse. 

 Individuals are not uncommon that show a distinctly paler belly, but 

 these belong to the common type, and since these lighter forms do not 

 intergrade with the white-bellied sports or produce them, they rank with 

 the common type with gray belly. 



Cages containing the original wild sports and their offspring have been 



