yi CONTENTS. 



PAGE 



Mesenteries 103 



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



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



Electrical Organs . . . . . . . .115 



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



Mesenchymatous Structures 132 



Skeleton 133 



Vertebral Column 134 



Ribs H3 



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. 



i 



Sub-phylum Vertebrata . . . . . . . . . .218 



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



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



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



Sub-Class II. Myxinoidei . . . . . 22^ 



Ostracodermi ..... ... 224 



Order I. Heterostraci . . . . . . 22 + 



Order II. Aspidocephali . . . . .22^ 



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



Series II. Gnathostomata . . . . . . . .22^ 



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



Class I. Pisces 22^ 



Sub-Class I. Elasmobranchii . . . . . 2]2 

 Order I. Cladoselachii . . . . 2 ^7 



Order II. Ichthyotomi . . . . j - 



Order III. Selachii -> 



Order IV. Holocephali ..... 2^0 



Sub-Class II. Teleostomi 2+2 



Legion I. Ganoidea ...... 248 



Order I. Crotsopterygtt .... 249 



Order II. Chondrostei . . . . 250 



( )rder III. Holostei . . . . . .25! 



Lr-ion II. Trlrostri 



Order 1. Ostariophy.si 2^4 



