Dermal papillae are regenerated and whiskers are produced after the experimental removal of up to the lower third of the vibrissa follicle, but if more of the follicle is removed neither event occurs (. Similarly, when lengths of the lower third of the vibrissa follicle wall are transplanted into ear skin, whiskers are again produced, but not if lengths of wall are taken from within the upper two-thirds of the follicle . From these experiments it was clear that the outer root sheath and the adherent mesenchymal layer, from which the new papillae are apparently derived, are the essential tissues in the regeneration process.