A few words of explanation are necessary with reference to the joint authorship of the book. The drawings and the investigations, where they are not referred to other observers, have been made by MR. A. AGASSIZ, the illustrations having been taken, with very few exceptions, from nature, in order to represent the animals, as far as possible, in their natural attitudes; and the text has been written by MRS. L. AGASSIZ, with the assistance of MR. A. AGASSIZ's notes and explanations. CAMBRIDGE, May, 1865. * * * * * NOTE. This second edition is a mere reprint of the first. A few mistakes accidentally overlooked have been corrected; an explanation of the abbreviations of the names of writers used after the scientific names has been added, as well as a list of the wood-cuts. The changes which have taken place in the opinions of scientific men with regard to the distribution of animal life in the ocean have been duly noticed in their appropriate place, but no attempt has been made to incorporate more important additions which the progress of our knowledge of Radiates may require hereafter. CAMBRIDGE, January, 1871. * * * * * CONTENTS. PAGE ON RADIATES IN GENERAL 1 GENERAL SKETCH OF THE POLYPS 5 ACTINOIDS 7 MADREPORIANS 16 HALCYONOIDS 19 GENERAL SKETCH OF ACALEPHS 21 CTENOPHORÆ 26 EMBRYOLOGY OF CTENOPHORÆ 34 DISCOPHORÆ 37 HYDROIDS 49 MODE OF CATCHING JELLY-FISHES 85 ECHINODERMS 91 HOLOTHURIANS 95 ECHINOIDS 101 STAR-FISHES 108 OPHIURANS 115 CRINOIDS 120 EMBRYOLOGY OF ECHINODERMS 123 DISTRIBUTION OF LIFE IN THE OCEAN 141 SYSTEMATIC TABLE 152 INDEX 154 LIST OF THE WOOD-CUTS. Unless otherwise specified, the illustrations are drawn from nature by ALEX. AGASSIZ. FIG. PAGE