CONTENTS. Xlil 



TAGE 



IV. THE ASCIDIANS iSo 



Structure of a Simple Ascidian iSi 



Test, Mantle, Atrium, Branchial Sac i8i 



Dorsal Lamina, Endostyle, and Peripharyngeal Band .... 1S3 



Visceral Anatomy iS6 



Nervous System and Hypophysis 1S8 



Circulatory System 191 



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 Papillje 204 



Cerebral Vesicle and its Sense-organs 204 



Comparison of Tunicate Eye with the Pineal Eye 207 



Stomodoeal and Atrial Involutions 209 



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



Clavehna and Ciona 214 



Metamorphosis of Ciona Intestinalis 215 



Vacuolization of the Notochord 216 



Mesenchyme and Body-cavity 217 



Preeoral Body-cavity and Praeoral Lobe 21 8 



Body-cavity of an Ascidian and Ccelom of Amphio.xus . . . 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 



