CONTENTS. MM 



IV. THE ASCIDIANS ............... 



STRUCTURE OF A SIMPLE ASCIDIAN ........... 181 



Test, Mantle, Atrium, Branchial Sac .......... 181 



Dorsal Lamina, Endostyle, and Peripharyngeal Band .... 183 



Visceral Anatomy ................ 186 



Nervous System and Hypophysis .......... 188 



Circulatory System ............... I9 1 



Renal Organs ................. 194 



Comparison between an Ascidian and Amphioxus ..... 194 



DEVELOPMENT OF ASCIDIANS ............. 196 



Segmentation and Gastrulation ........... 197 



Formation of Medullary Tube and Notochord ...... 198 



Origin of Mesoderm ............... 199 



Outgrowth of Tail ............... 201 



Formation of the Adhesive Papilla .......... 204 



Cerebral Vesicle and its Sense-organs ......... 204 



Comparison of Tunicate Eye with the Pineal Eye ..... 207 



Stomodceal and Atrial Involutions .......... 209 



Formation of Alimentary Canal and Hatching of Larva. . . 214 



Clavelina and Ciona ............... 214 



METAMORPHOSIS OF CIONA INTESTINALIS ......... 215 



Vacuolization of the Notochord ........... 216 



Mesenchyme and Body-cavity ........... 217 



Pneoral Body-cavity and Prteoral Lobe ........ 218 



Body-cavity of an Ascidian and Coalom of Amphioxus . . . 220 



Fixation of the Ascidian Larva ........... 222 



Reopening of Neuropore; Degeneration of Cerebral Vesicle; 



Formation of Definitive Ganglion ........ 223 



Primary Topographical Relations and Change of Axis . . . 226 



Formation of Additional Branchial Stigmata ...... 229 



First Appearance of Musculature .......... 235 



Alimentary Canal and Pyloric Gland ......... 235 



Appendicularia ................ 236 



Abbreviated Ontogeny of Clavelina .......... 239 



NOTES ..................... 240 



