Acknowledgments

To my supervisor at University College, London, Professor D. M. S. Watson, F.R.S., I am deeply grateful for advice and encouragement. My thanks are also due to the following: The Minister of Internal Affairs, Wellington, for permission to collect and export specimens of Leiopelma; Mr. E. G. Turbott, M.Sc., of the Auckland War Memorial Museum, for the loan of two adult specimens of Ascaphus truei, the X-ray photographs of which have been extremely useful; Dr. W. Wallace Main and Mr. B. N. Gibson, of Auckland, and Mr. Venning, of the Department of Anatomy, University College, London, who prepared X-ray negatives for me; Mr. W. A. Brackenbury, of the

Department of Zoology, University College, London, for a photograph of the vertebral column.