CONTENTS 



SECTION XIII 



PACK 



Phylum Chokdata .... . . . i 



Sub-phylum and Class I. Hemichorda (Adelochorda) 2 



Sub-phylum and Class II. Urochorda 14 



1. Example of the Class — Ascidia ... . . 14 



2. Distinctive Characters and Classification . . . 21 

 Systematic position of the Example . . .24 



3. General Organisation ... . . 24 



Sub-phylum III. Euchorda ... . . 43 



Section I. Acbania . . .44 



Section II. Craniata . . , ... 65 



Class I. Cyclostomata ... . ... 123 



1. Exampls of the Class — Petromyzo)i 124 



2. Distinctive Characters and Classification . . . 137 



3. Comparison of the Myxinoids with the Lamprey . . 138 



4. General Remarks 142 



Class II. Pisces .... . 144 



Sub-class I. Elasmobranchii .... 144 



1. Example of the Sub-class — Scyllmm (■<(iiii:ula or HemimyUiuni 



modestum .... . 144 



2. Distinctive Characters and Classification ■. . . 166 



3. General Organisation . .... 170 



