CHAPTER XVIL 



THE ANCESTKAL SEKIES OF MAN. 



II. FBOM 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 (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, Acoelomi and Coalomati : the former 

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

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

 Descent of the Ccelomati from the Acoelomi. 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 Intestinal Tube into Gill-intes- 

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

 donia). Ascidian Larva exhibits the Outline of a Choi-da- 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. 

 Skull-less Animals (Acrania) and Skulled Animals (Craniota) . Ninth 

 Ancestral Stage : Skull-less Animals. Amphioxns and Primitive Verte- 

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

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

 to the Cyclostomi (Hyxinoidm and Petromyzonidcs). 



u 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, 

 Is crushed and buried by the traveller's heel. 



