Abstract
1) In the mouse, melanoblasts positive to the dopa-oxidase reaction appear in the basal layer of the epidermis at neo-natal stages, though they can not be detected in the epidermis of adult mice.
2) There was a significant difference in the number of the dopa-positive melanoblasts per unit area of the epidermis at the neo-natal stages between the two strains examined, C3H/HeNSa and C57BL/6.
3) The difference seems to be attributable to the difference in dopa-oxidase activity of the epidermal melanoblasts from the two strains as determined microspectrophotometrically.
4) The F1 from the reciprocal crosses between the two strains exhibited an intermediate value in both the number of dopa-positive cells and the enzyme activity of the cells.
5) The F2 showed a considerably wider distribution in the number of dopa-positive cells.
6) These results seem to suggest an inhibitory factor is involved in the strain difference in the dopa-oxidase activity and is controlled by more than two loci.
