C(ELOMATA. 33 



Subgrade B. CCELOMATA. (Triploblastica). 



Bilaterally symmetrical forms with a praeoral region (head). A third 

 cellular body-layer, the mesoderm, present between the embryonic ecto- 

 derm and mesoderm. Within this a body-cavity (coelom) is usually 

 developed outside the digestive cavity. 



