II. THE INHERITANCE OF WHITE-SPOTTING IN RABBITS, 



WITH SPECIAL REFERENCE TO GAMETIC 



CONTAMINATION.' 



One of the commonest color variations of mammals is white- 

 spotting the occurrence of wholly unpigmented areas in the skin and 

 the hair arising from it. Small unpigmented areas are frequently 

 found in the coats of wild mammals, as, for example, in the fur of wild 

 mice, rats, the common North American rabbit (Lepus sylvaticus), 

 and cavies (e.g., Cavia cutleri). The white-spotting found in these 

 wild forms is usually not extensive. It consists of a white "star" 

 in the forehead or a spot on the chest, or at the end of the tail, or on 

 a foot. Such locations of the white-spotting suggest a deficiency of 

 pigment in the skin, either where it closes together in the median line 

 during development of the embryo or at the extreme limits of its 

 peripheral extension during development. At places where the skin 

 regenerates after injury, even in self-colored animals, a white spot 

 frequency develops. This is especially noticeable on the backs and 

 shoulders of horses where the harness has "galled" them. That such 

 slight congenital deficiencies of pigment as occur in wild mammals 

 are hereditary has been shown by Little in the case of the house- 

 mouse, and by Phillips and myself (unpublished observations) in the 

 case of the field-mouse, Peromyscus. We observed in a colony of 

 Peromyscus reared from animals taken in Massachusetts the occur- 

 rence of individuals having tails partly or wholly white. This con- 

 dition was found to be a Mendelian recessive character in crosses. 

 After one or two selections of white-tailed individuals, we noted exten- 

 sion of the white area on to the belly. 



In some wild mammals the white-spotting is more extensive, taking 

 the form of a definite pattern, as in skunks, the harp-seal, and the 

 Malay tapir. The color pattern of skunks, while characteristic, is 

 known to vary slightly, the value of a pelt increasing with the amount 

 of black which it contains, a fact which the incipient industry of 

 skunk-farming in the United States notes with interest. Selective 

 breeding is being directed toward the establishment of all-black 

 strains and no doubt it will ultimately be successful. 



White-spotting is so common in the domestic animals as to need 

 no comment. White-spotting in more or less definite patterns char- 

 acterizes the majority of our breeds of cattle, horses, dogs, and swine. 

 Often the pattern is so definite and so strongly inherited as to con- 

 stitute a sort of trade-mark of breed purity, as in Hereford (white- 

 faced) cattle, Dutch belted cattle, and Dalmatian coach-dogs. Much 



1 Valuable assistance in the conduct of this investigation was given by my former pupil, Prof. 

 H. D. Fish. 

 4 



