138 



ZOOLOGY 



SECT. 



enteron (ent. cav') and being lined with endoderm. From such a 

 form the actual condition of things found in the medusa would be 

 produced by the continuous cavity in the bell being for the most 

 part obliterated by the growing together of its walls so as to form 



rcvcUcce 



radius 



ad-rcuiciMf \ 



CrUtffOsdsiios \ 



SUb-radiu,j> » „ ^ 



a-d- radiws 



sub radius 

 ptr- ra dius — 



Fig 102.^Projections of polype (A) and medusa (B), showing the various orders of radii; 

 gon. gonad ; mnb. manubrium. 



the endoderm-lamella (D', end. lam), and remaining only along 

 four meridional areas — the radial canals (rad. c), and a circular 

 area close to the edge of the bell — the circular canal (cir. c). 



While both polype and medusa are radially symmetrical, the increase in 

 complexity of the medusa is accompanied by a differentiation of the structures 

 lying along certain radii. If a polype is projected on a plane surface (Fig. 102, A), 



