1. Follicles go through cycles of growth, degeneration and rest, and then regeneration and another growth phase. During growth, the follicle cells divide to create the hair shaft. The natural length of this shaft is controlled by the extent of this phase. To conserve energy, in most animals, growth stops when the shaft reaches an appropriate length, the follicle degenerates, the hair shaft is held in the skin and the follicle goes into its rest phase.
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