PORIFERA (_CONTINUED_): FORMS OF SPICULES—CALCAREA—HOMOCOELA —HETEROCOELA—HEXACTINELLIDA—DEMOSPONGIAE—TETRACTINELLIDA —MONAXONIDA—CERATOSA—KEY TO BRITISH GENERA OF SPONGES 183 CHAPTER IX PORIFERA (_CONTINUED_): REPRODUCTION, SEXUAL AND ASEXUAL—PHYSIOLOGY —DISTRIBUTION—FLINTS 226 COELENTERATA CHAPTER X COELENTERATA—INTRODUCTION—CLASSIFICATION—HYDROZOA—ELEUTHEROBLASTEA —MILLEPORINA—GYMNOBLASTEA—CALYPTOBLASTEA— GRAPTOLITOIDEA —STYLASTERINA 245 CHAPTER XI HYDROZOA (_CONTINUED_): TRACHOMEDUSAE—NARCOMEDUSAE—SIPHONOPHORA 288 CHAPTER XII COELENTERATA (_CONTINUED_): SCYPHOZOA = SCYPHOMEDUSAE 310 CHAPTER XIII COELENTERATA (_CONTINUED_): ANTHOZOA = ACTINOZOA—GENERAL CHARACTERS —ALCYONARIA 326 CHAPTER XIV ANTHOZOA (_CONTINUED_): ZOANTHARIA 365 CTENOPHORA CHAPTER XV CTENOPHORA 412 ECHINODERMATA CHAPTER XVI ECHINODERMATA—INTRODUCTION—CLASSIFICATION—ANATOMY OF A STARFISH —SYSTEMATIC ACCOUNT OF ASTEROIDEA 427 CHAPTER XVII ECHINODERMATA (_CONTINUED_): OPHIUROIDEA = BRITTLE STARS 477 CHAPTER XVIII ECHINODERMATA (_CONTINUED_): ECHINOIDEA = SEA-URCHINS 503 CHAPTER XIX ECHINODERMATA (_CONTINUED_): HOLOTHUROIDEA = SEA-CUCUMBERS 560 CHAPTER XX ECHINODERMATA (_CONTINUED_): PELMATOZOA—CRINOIDEA = SEA-LILIES —THECOIDEA—CARPOIDEA—CYSTOIDEA—BLASTOIDEA 579 CHAPTER XXI ECHINODERMATA (_CONTINUED_): DEVELOPMENT AND PHYLOGENY 601 INDEX 625 SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK _The names of extinct groups are printed in italics._ PROTOZOA (pp. 1, 48).