178. Sea-urchin resorbing the arms of the larva 133 179-181. Successive stages of young Sea-urchin 133, 134 182. Ophiuran which has nearly resorbed the larva 135 183. Larva of Ophiuran (Pluteus) 136 184. Young Ophiuran 137 185. Cluster of eggs of Star-fishes over mouth of parent 137 Diagram of a rocky beach 149 ABBREVIATIONS OF THE NAMES OF AUTHORS. AG. L. Agassiz. A. AG. A. Agassiz. AYRES W. O. Ayres. BLAINV. Blainville. BOSC Bosc. BR. Brandt. CLARK H. J. Clark. CUV. Cuvier. D. & K. Düben and Koren. EDW. Milne-Edwards. FORBES Edw. Forbes. GRAY J. E. Gray. JAEG. Jaeger. LAM. Lamarck. LAMX. Lamouroux. LIN. Linnæus. LYM. Lyman. M. & T. Müller and Troschel. MILL. Miller. PÉR. et LES. Péron and Lesueur. SARS M. Sars. STIMP. Stimpson. TIL. Tilesius. * * * * * MARINE ANIMALS OF MASSACHUSETTS BAY. ON RADIATES IN GENERAL. It is perhaps not strange that the Radiates, a type of animals whose home is in the sea, many of whom are so diminutive in size, and so light and evanescent in substance, that they are hardly to be distinguished from the element in which they live, should have been among the last to attract the attention of naturalists. Neither is it surprising to those who know something of the history of these animals, that when the investigation of their structure was once begun, when some insight was gained into their complex life, their association in fixed or floating communities, their wonderful processes of development uniting the most dissimilar individuals in one and the same cycle of growth, their study should have become one of the most fascinating pursuits of modern science, and have engaged the attention of some of the most original investigators during the last half century. It is true that from the earliest days of Natural History, the more conspicuous and easily accessible of these animals attracted notice and found their way into the scientific works of the time. Even Aristotle describes some of them under the names of Acalephæ and Knidæ, and later observers have added something, here and there, to our knowledge on the subject; but it is only within the last fifty years that their complicated history has been unravelled, and the facts concerning them presented in their true connection.