The Results of Crosses between Inbred Strains of Guinea Pigs, Differing in Number of Digits.

Guinea pigs normally have only 3 toes on the hind feet. This is the condition in all of the wild species of the family Caviidae. Atavistic return of the little toe is not, however, especially uncommon. CASTLE (1906) noticed an animal with an imperfect little toe and by inbreeding and selection developed a strain in which every animal had 4 perfect digits on the hind feet. Strain D, in my possession, traces exclusively to 3 animals of this strain, kindly presented by Professor CASTLE in 1915. It has bred true to the 4-toed condition to the present time. As there have seldom been more than 2 or 3 breeding males at a time, there has been much inbreeding. It may safely be assumed to be homozygous in most respects.