vi CONTENTS. 



PAGE 



Mesenteries - ... 103 



Splanchnocoele .......... 106 



Muscular System ......... 107 



Electrical Organs . . . . . . . .115 



Urogenital Organs . . . . . . . . .116 



Mesenchymatous Structures . . . . . . . .132 



Skeleton ........... 133 



Vertebral Column ........ 134 



Ribs . . . . . . . . . . .143 



Sternum .......... 147 



Skull 150 



Appendicular Skeleton ....... 167 



Organs of Circulation . . . . . . . .178 



Heart 184 



Aortic Arches .......... 185 



Arteries .......... 188 



Veins . . . . . . . . . . .192 



Lymph System ......... 198 



The Segmentation of the Head ....... 201 



The Early History of the Ovum ....... 205 



The Origin of the Vertebrates . . . . . . . .215 



PART II. CLASSIFICATION OF VERTEBRATES. 



Sub-phylum Vertebra ta . . . . . . , . . .218 



Series I. Cyclostomata . . . . . . . , .219 



Class I. Marsipobranchii . . . . . '. .219 



Sub-Class I. Petromyzontes ..... 223 



Sub-Class II. Myxinoidei ...... 224 



Ostracodermi ..... ... 224 



Order I. Heterostraci . . . . . .224 



Order II. Aspidocephali . . . . .2215 



Order III. Antiarcha . . . . . .22^ 



Series II. Gnathostomata . . . . . . . .225 



Grade I. Ichthyopsida . . . . . . . . 226 



Class I. Pisces ......... 227 



Sub-Class I. Elasmobranchii ..... 232 



Order I. Cladoselachii ..... 237 



Order II. Ichthyotomi ..... 237 



Order III. Selachii 238 



Order IV. Holocephali . . . . . 240 



Sub-Class II. Teleostomi 242 



Legion I. Ganoidea ...... 248 



Order I. Crossopterygii ..... 249 



Order II. Chondrostei 250 



Order III. Holostei . . . . .251 

 Legion II. Teleostei ...... 252 



Order I. Ostariophysi ..... 254 



