CCELENTERATA. 



171 



--WUS. 



FIG. 80. Sections of types of Ccelenterates (diagrammatic) : i (longitudinal) and 2 

 (transverse) of a tubular hydroid; 3, Sea Anemone (longitudinal); 4, same (transverse, 

 at the level of the upper dotted line) ; 5, same (transverse, at the level of the lower 

 dotted line); 6, longitudinal or vertical section of a Medusa; 7, transverse section 

 of same at the level of ih$ dotted line. The continuous line is ectoderm, the broken 

 line, entoderm, and the stippled portion, mesenchyma. c.c., circular canal; g, gullet; 

 g.i'., gastrovascular cavity; m, mouth; ma., manubrium; mes., mesentery; mes. 1 , direc- 

 tive mesentery; o, ostium; r.c., radial canal; *, tentacle; v, velum. 



Questions on the figures. By a careful comparison of the diagrams 

 what points of similarity do you find in these three types? What are the 

 principal points of difference? Examine similar diagrams in other texts. 

 Why is Coalenteraie an appropriate name for all? 



may float freely. The second type is the active jelly-fish, or 

 medusoid (bell) type. The medusae, though varying greatly 

 as to details agree in having a shape comparable to that of 

 an umbrella or a bell. The convex surface is normally the 

 upper surface. At the margin of the umbrella are tentacles 

 often very numerous, and frequently much elongated. In the 

 middle of the concave surface is a projection, at the lower end 

 of which is the mouth-opening. The gullet leads from the 

 mouth into a cavity in the central portion of the body of the 

 bell (gastro-vascular cavity}. From the central cavity 



