LIST OF ILLUSTRATIONS xxi 



PIG. 



82. Sycon gelatinosum, pore-membrane . . . 109 



83. ,, ,, apopyle . 109 



84. External form of various Sponges . . .115 



85. Ascetta primordialis ...... . 116 



86. Diagrams of canal-system of various Sponges . .117 



87. Vertical Section of Spongilla .... . . 118 



88. Cells of ectoderm of Sponge . . . . . . 119 



89. Development of tri-radiate spicule ... . 120 



90. Skeleton of various Sponges . . 121 



91. Various forms of Sponge spicules . 122 



92. Pheronema Carpenter! . . ... 123 



93. Larva of Clathrina blanca . ... ... 124 



94. Development of Sycoii raphanus . 125 



95. Obelia . . .130 



96. ,, Vertical section of polype .... ... 132 



97. Nematocysts of Hydra . . . 133 



98. Tentacle of Eucopella . 134 



99. Obelia, medusa ........ . . 135 



100. Diagram of medusa ... . 136 



101. Derivation of medusa from polype . 137 



102. Projections of polype and medusa. . . 138 



103. Development of zoophyte . . . 140 



104. Bougainvillea ramosa . . . . 144 



105. Various forms of Leptolinre . . 145 



106. Ceratella . . 146 



107. Hydra . . .147 



108. Protohydra leuckartii ... . . 148 



109. Various forms of leptoline Medusas ... . 150 



110. Diagram illustrating formation of sporosac by degeneration of 



medusa ............. 151 



111. Early development of Eucope .... . 152 

 1J2. Two Trachymedusje . . . 154 



113. Two Narcomedusse ..... . 154 



114. ^Eginura, tentaculocyst ... . 155 



115. Larva of ^Eginopsis ... . . 156 



116. Millepora alcicornis, skeleton . . .157 



117. Millepora, diagram of structure . .158 



118. Stylaster sanguineus, skeleton . . 159 



119. Halistemma tergestinum .... . 160 



120. Diagram of a Siphonophore . . . . . . 162 



121. Development of Halistemma ...... . . 163 



122. Physalia .... .164 



123. Diphyes campanulata ..... . . 165 



124. Porpita pacifica ......... . 166 



125. Graptolites ..... . 167 



126. Aurelia aurita, dorsal and ventral views . . . . 169 



127. ,, ,, side view and vertical section ..... 171 



128. ,, ,, portion of umbrella with tentaculocyst . .172 



