i88 



ZOOLOGY 



have changed the land contours by additions of marginal reefs. 

 Much of the limestone of the crust of the earth is from corals. 



FIG. 87. 



s.b 



r.z: 



FIG. 87. A very diagrammatic and generalized illustration of a complex coelenterate colony. 

 The shaded portion represents the gastro-vascular cavity. The light portion, the body tissues. 

 b., a bell-like individual developed into an air-bladder; m. t mouth; n.z., nutritive individual; p.*.. 

 protective individual; r.z. 1 , r.z.*, r. z.* f different types of reproductive individuals; s.b., swimming 

 bell; /, tentacles, which are sensory and protective structures. After Lang. 



Questions on the figure. What is meant by "generalized" above? How does 

 such a polymorphic colony as this differ from a highly organized individual? 

 In what respect is it similar to an individual ? What is the function of the gastro- 

 vascular system? What is the gain in its wide distribution through the colony? 

 How do the Siphonophora differ from the other colonial coelenterates ? 



