Abstract
Each of 98 virgin female albino mice was presented for the first and only time with a 10-day old pup that had been randomly selected, shaven or unshaven, and killed by freezing. From analyzing the principal parental activities, it emerged that the shaven pup more than its unshaven litter-mate stimulated retrieving and nest-building. The greater infantile effectiveness was clearly linked to the lack of fur. The behaviour of the females seemed to evince uncertainty, consistent with the hypothesis that the shaven pup releases not only signals proper to its age but also a signal of younger age.