*Professor O. W. Tiegs, F.R.S., died on 5 November 1956, when he had completed, in manuscript, a first draft of a review on arthropod evolution. The present article is an emended extension of this manuscript. I gratefully acknowledge the assistance rendered to me by many colleagues, in particular Dr F. H. Drummond, and other Melbourne colleagues of Professor Tiegs, for preparing a typescript of his manuscript, Dr J. T. Temple, Dr O. Evans and Dr D. T. Anderson, for preparing a typescript of his manuscript, Dr J. T. Temple, Dr O. Evans and Dr D. T. Anderson, who have checked some of the data, Professor O. M. B. Bulman, F.R.S. and Dr C. J. Stubblefield, F.R.S. for reading the manuscript and making further suggestions, and Dr J. P. Harding for similar services and assistance with the photography employed in preparing the figures. S.M.M.
S. M. MANTON
Department of Zoology, King's College, University of London and British Museum (Natural History)