XIV CONTENTS. 



fAGE 



V. THE PROTOCHORDATA IN THEIR RELATION TO THE 



PROBLEM OF VERTEBRATE DESCENT 242 



Balanoglossus 242 



External Features 242 



Nervous System and Gonads 244 



Metamerism 246 



Body-cavities; Proboscis-pore; Collar-pores 247 



Alimentary Canal 249 



Development; the Tornaria Larva 250 



The Larva of Asterias Vulgaris; Water-pores and Prreoral 



Lobe 253 



Apical Plate of Tornaria 255 



Metamorphosis of Tornaria 256 



The Nemertines 256 



Cephalodiscus and Rhabdoi'Leura 261 



The Pr/eoral Lobe of Echinoderji Larv.e 267 



The Pr.eoral Lobe of the Protochordates 271 



Anterior and Posterior Neurenteric Canals, and the Position of 



the Mouth in the Protochordates 274 



The Pr.eoral Lobe in the Craniate Vertebr-Ates .... 279 



The Mouth of the Craniate Verteekaies 2S0 



Significance of the Hypophysis Cerebri 2S3 



The Ascidian Ihpophysis ... 2S7 



Conclusion 2S9 



Notes . . 

 References 



Index 



291 



291; 



ii I 



