CHAPTER XVII. 



THE ANOESTEAL SEBIES OP MAN. 



II. — From the Peimitive Worm to the Skulled Animai.. 



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

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

 Animals (Sponges and Sea-Nettles), in the other the Parent Form of 

 Worms. — Eadiate 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 Cayity and Blood-vessel System. — 

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

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

 (^Tunicata) and Chorda- Animals (Ohord^onia) . — Seventh Stage: Soft- 

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

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

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

 doma). — Asoidiau Larva exhibits the Outline of a Chorda-Animal, — 

 Construction of the Notochord. — Mantled Animals and Vertebrates as 

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

 the other Higher Animal Tribes (Articulated Animals, Star-Animals, 

 Soft-bodied Animals). — Significance of the Metameric Formation. — 

 Sknll-less Animals (Acrania) and Skulled Animals (Craniota). — Ninth 

 Ancestral Stage : Skull-less Animals. — Amphioxus and Primitive Verte- 

 brate. — Development of Skulled Animals (Construction of the Head, 

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

 to the Cyclostomi (Myxinoidw and Fetromyzonidce). 



" Not like the gods am I ! Full well I know j 

 But like the worm which in the dust must go, 

 And, finding in the dust his life and weal, 

 Is crashed and buried by the traveller's heel. — 



