CHAPTER XVIL 

 THE ANCESTRAL SERIES OF MAN. 



11. Feom the Primitive Worm to the Skulled Animal. 



The Four Higher Animal Tribes are descended from the Worm Tribe. — The 

 Descendants of the Gastraea; in one direction the Parent Form of Plant- 

 Animals (Spongea and Sea-Nettles), in the other the Parent Fortn of 

 Worms. — Radiate form of the former, Bilateral form of the latter. — The 

 Two Main Divisions of the Worms, Acoelomi and Coelomati : the former. 

 without, the latter with, a Body Cavity and Blood vessel System. — 

 Sixth Ancestral Stage : Archelminthes, most nearly allied to Turbellaria. 

 — Descent of the Coelomati from the Accelomi. — Mantled Animals 

 {Tunicata) and Chorda-Animals (Chordonia). — Seventh Stage: Soft- 

 Worms (Scolecida). — A Side Branch of the Latter: the Acorn- Worm 

 (Balanoglossus). — Differentiation of the lutestiual Tube into Gill-intes- 

 tine and Stomach-intestine. — Eighth Stage : Chorda- Animals (Chor- 

 doma). — Ascidian Larva exhibits tlie Oatline of a Cliorda-Animal. — 

 Construction of the Notochord. — Mantled Animals and Vertebrates as 

 Diverging Branches of Chorda-Animals. — Separation of Vertebrates from 

 the other Higher Animal I'ribes (Articulated Animals, Star-Animals, 

 Suft-bodied Animals). — Significance of tho Metameiic Formation. — 

 Skull-less Animals (Acrania) and Skulled Animals (Craniota), — Kinth 

 Ancestral ^tage : Skull-less Animals. — Amphioxus and Pi-imitive Verte- 

 brate. — Devt'lopment of Skulled Animals (Construction of the Head, 

 Skull, and Brain). — Tenth Ancestial Stage: Skulled Animals, allied 

 to the Cyclostomi {Myxinoidce and I'etromyzonidas). 



** Not like the gods am I ! Full well I know 5 

 But like the worm which in the dust must go. 

 And, finding in the dust his life and \ve;il, 

 Is crushed and buried by the traveller's heel. — • 



