Metamorphosis

Metamorphosis was a change undergone by some life-forms. Caterpillars underwent a metamorphosis into a butterfly, as did giant maggots into giant flies. (TV: The Green Death) Solonians experienced "accelerated genetic metamorphosis" seasonally. (TV: The Mutants) The Wirrn also underwent metamorphosis. (TV: The Ark in Space)

The newly regenerated Second Doctor compared his change to a butterfly leaving its chrysalis. (TV: The Power of the Daleks) Both Mawdryn and the newly regenerated Sixth Doctor also compared regeneration to metamorphosis. (TV: Mawdryn Undead, The Twin Dilemma)

Rutan scouts were specially trained in metamorphosis techniques. (TV: Horror of Fang Rock)

Princess Astra of Atrios, realising that she was the sixth segment of the Key to Time, referred to her "metamorphosis". (TV: The Armageddon Factor)