CLASSIFICATION OF ANIMALS 577 



sented it as possessed of one main trunk with all of the branches springing 

 from it. The relationship between the various phyla above the coelen- 

 terates is so uncertain that in the present state of our knowledge it seems 

 impossible to present exact continuity here. In interpreting such a 

 diagram the fact should also be borne in- mind that no existing type is 

 ancestral to any other existing type but that if the two are related this 

 relationship is through a common ancestor, now extinct. With these 

 facts in mind the accompanying scheme (Fig. 394) is presented. 



