Sentence:  Regeneration in the animal kingdom always requires a "wound stimulus". Regrowth of antlers is no exception, the wounded pedicle exposed by the casting of the previous set of antlers serving as a vital stimulus for renewal of antler growth. This was convincingly demonstrated in congenitally polled (‘<WSD>hummel</WSD>') red deer, which lack antlers, have pedicles, and can be induced to form a set of antlers if the tips of the pedicles are amputated. 
Meaning of the word marked with <WSD> tags:  A stag that has failed to grow antlers; a cow that has not developed horns. (from late 15th c.)