576 



GENERAL CONSIDERATIONS 



Verfebrata 



Cephalochorda ia 



Arfhropoda 



Annelio/of 

 Chaefogna^ha 



Urochordata 



Mollusca 



Echinodermafa 

 (Secondary Raa/ial) 



Brachiopoda 



Bryozoa 



True Coelom 



Nemer-ti'neoi 

 (CoelomFJ 



Nemafhelmin fhes 

 (Body Cavity) 



Plafyhelmin fhes 



Cfenophora 

 (Biradial) 



Rofifera 

 (Body Cavii-y) 



Alimentary Canal 



Bilateral Symmetry 

 Triploblastic 



Coelenterata 

 {Radial) 



_pi2lob/astic 



Porifera 

 (Radial) 



First Life 

 Fig. 394. — Diagram of a phylogenetic tree illustrating one conception of the relation- 

 ship of the animal phyla, and also suggesting the uncertainty attending the relationship 

 of most of the different phyla above the Coelenterata. Levels of organization are indicated 

 by horizontal lines of dashes. Retrogression is suggested by the branch turning downward. 

 Enteropneusta is a class of Hemichordata which includes Balanoglossue. 



