What is not so generally taken into consideration is that the assemblage is formed by the agglutinations of millions of years, and that it is hence composed of parts of different ages and pedigrees, some exceedingly ancient and hoary, some middle-aged, and some relatively new and recent.

In other words, the daughter cells of the constituents of the rete Malpighii which have grown into the corium pass through a degeneration precisely similar to that undergone by cells shed at desquamation, or those which eventually give rise by their agglutination to a hair.