CHAPTER XVII. 

 THE ANCESTRAL SERIES OF MAN. 



II. FKOM THE PRIMITIVE WOEM TO THE SKULLED ANIMAL. 



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

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

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

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

 Two Main Divisions of the Worms, Accelomi and Ccelomati: the former 

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

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

 Descent of the Coelomati from the Acrelorni. Mantled Animals 

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

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

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

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

 donia). Ascidian 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 tho Metameric Formation. 

 Skull-less Animals (Acrania) and Skulled Animals (Cran iota) .Ninth 

 Ancestral ^ t:ige : Sknll-less Animals. Amphioxus and Primitive Verte- 

 brate. Development of Skulled Animals (Construction 01' the Head, 

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

 to the Cyclostomi (Myxinuidov and 1'etromyzonidce), 



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

 But like the worm which in the dust must go, 

 And, finding in the dust his life and weal, 

 IB crushed and buried by the traveller's heel. 



