Through a series of interrogatories, unsolved problems of antler evolution, anatomy, development, physiology, and pathology are probed, with commentaries, on the following prospects for future research: 1. How could these improbable appendages have evolved mechanisms to commit suicide, jettison the corpse, and regenerate new ones every year? 2. By what developmental processes are antlers able to prescribe their own morphogenesis with mirror image accuracy year after year and in some cases produce deliberate asymmetries? 3. What causes the scalp to transform into velvet skin as a deer's first antlers develop? 4. Why do healing pedicle stumps give rise to antler buds instead of scar tissue? 5. How is the unprecedented rate of antler elongation related to the diameter and length of the structure to be grown? 6. How come wound healing by pedicle skin is held in abeyance for several months until new growth resumes? 7. How is it that tropical deer regenerate antlers at any time of year, while in temperate zones deer do so in seasonal unison? 8. How do deer find enough calcium to make such massive antlers in only a few months? 9. What is the nature of the bizarre tumors that some antlers grow following castration?
A landmark in the history of regeneration has been the discovery that the fingertips of young children are capable of growing back after a m p u t a t i~n .~~~~ This remarkable result is achieved simply by avoiding the heretofore standard surgical procedure of suturing flaps of skin over the When the amputation surface is left raw with suitable dressings, healing occurs in part by wound contraction but in large measure by epidermal migration over the exposed mesodermal tissues. This leads to the replacement of the fingertip in a matter of weeks, including the development of fingerprints and the production of a new fingernail (Fig. 1). Not surprisingly, the original length of the finger is seldom restored. Evidence thus far available indicates that the best results are obtained in the youngest children and that regeneration is possible only after amputation distal to the last joint of the finger.25The clinical implications of this phenomenon with respect to the possibilities for regeneration in other human appendages depend in large measure on whether the replacement of fingertips in children is a true case of epimorphic regeneration or simply an impressive instance of wound healing and Professor of Biology and Dean
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