CONTENTS. 
PAGE 
Introduction, ............ 5 
History, ........... 5 
Bibliography, ........... 8 
Anatomy, ........... 12 
Classification, . . .. . . . . . .12 
The Colony, . . . . . . . . . .12 
The Test, .......... 13 
The Ascidiozooid, . . . . . . . . .15 
The Mantle, . . . . . . . . . .17 
The Branchial Sac, . . . . . . . . .18 
The Endostyle, . . . . . . . . . .19 
The Dorsal Lamina, . . . . . . . . .19 
The Tentacles, .......... 20 
The Hervous System, &c., ........ 20 
The Alimentary Canal, . . . . . . . .21 
The Blood, &c., .......... 22 
The Eeproductive Organs, . . . . . . . .23 
Gemmation, .......... 24 
Description of the Species, &c., ......... 27 
Ascidise Compositse, .......... 28 
Botryllidie, . . . . , ... . . .33 
Botrylloides, . . . . . . . . . .38 
Sarcohotrylluide>s, . . . . . . . . .56 
Polycycliis, . . . . . . . . . .61 
Distomidie, .......... 69 
Colella, .......... 72 
Anatomy and Histology of Co/eKa . . . . .77 
Anatomy and Histology of Oolella thomsoni, . ... . .95 
DistapUa, .......... 126 
Genus doubtful, . . . . . . . .132 
Cystodytes, . . . . . . . . . .135 
Sijmplegma, .......... 144 
Pol.vclinidse, . . . . . . . . . .148 
Pharyngodictyon, . . . . . . . . .152 
Tylohranchion, ......... 157 
Atupogaster, . . . . . . . . . .163 
Morchellioides, . . . . . . . . .176 
