THE CAMBRIDGE NATURAL HISTORY EDITED BY S. F. HARMER, Sc.D., F.R.S., Fellow of King’s College, Cambridge; Keeper of the Department of Zoology in the British Museum (Natural History) AND A. E. SHIPLEY, M.A., Fellow and Tutor of Christ’s College, Cambridge; Reader in Zoology in the University VOLUME IV [Illustration: Signet] MACMILLAN AND CO., LIMITED LONDON · BOMBAY · CALCUTTA MELBOURNE THE MACMILLAN COMPANY NEW YORK · BOSTON · CHICAGO ATLANTA · SAN FRANCISCO THE MACMILLAN CO. OF CANADA, LTD. TORONTO CRUSTACEA By GEOFFREY SMITH, M.A. (Oxon.), Fellow of New College, Oxford; and the late W. F. R. WELDON, M.A. (D.Sc., Oxon.), formerly Fellow of St. John’s College, Cambridge, and Linacre Professor of Human and Comparative Anatomy, Oxford TRILOBITES By HENRY WOODS, M.A., St. John’s College, Cambridge; University Lecturer in Palaeozoology INTRODUCTION TO ARACHNIDA, AND KING-CRABS By A. E. SHIPLEY, M.A., F.R.S., Fellow and Tutor of Christ’s College, Cambridge; Reader in Zoology EURYPTERIDA By HENRY WOODS, M.A., St. John’s College, Cambridge; University Lecturer in Palaeozoology SCORPIONS, SPIDERS, MITES, TICKS, ETC. By CECIL WARBURTON, M.A., Christ’s College, Cambridge; Zoologist to the Royal Agricultural Society TARDIGRADA (WATER-BEARS) By A. E. SHIPLEY, M.A., F.R.S., Fellow and Tutor of Christ’s College, Cambridge; Reader in Zoology PENTASTOMIDA By A. E. SHIPLEY, M.A., F.R.S., Fellow and Tutor of Christ’s College, Cambridge; Reader in Zoology PYCNOGONIDA By D’ARCY W. THOMPSON, C.B., M.A., Trinity College, Cambridge; Professor of Natural History in University College, Dundee MACMILLAN AND CO., LIMITED ST. MARTIN’S STREET, LONDON 1909 All the ingenious men, and all the scientific men, and all the fanciful men, in the world, with all the old German bogypainters into the bargain, could never invent ... anything so curious, and so ridiculous, as a lobster. CHARLES KINGSLEY, _The Water-Babies_. For, Spider, thou art like the poet poor, Whom thou hast help’d in song. Both busily, our needful food to win, We work, as Nature taught, with ceaseless pains, Thy bowels thou dost spin, I spin my brains. SOUTHEY, _To a Spider_.