138 



ZOOLOGY 



SECT. 



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

 form the acttial 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 



raxiccce 



tactbU/G 



ad-ra-d-Lics \ 



Sub-radiiL£ ^ ^ ^> 

 a,d- radiws 



suiradiuyf 



per-radlus 



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

 gon. gonad ; fimh. manubrium. 



the endoderm-lamella (C, avJ. Icmi), and remaining only along 

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

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



While Ijoth 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), 



