IV 



PHYLUM OELENTERATA 



109 



of the umbrella is fringed by numerous close-set marginal 

 tentacles (/). 



In the centre of the lower or sub-umbrella surface is a 

 four-sided aperture, the mouth (mtli), borne at the end of 



99" 



FIG. 51. Aurelia aurita. Ventral view two of the oral arms are removed; tt.r.c, 

 radial canal; gon, gonads; i.r.c, radial canal; mg. Ifi, marginal lappet; mth t 

 mouth; or. a, oral arm; p.r.c, radial canal; s.g.p, sub-genital pit; /, 

 tentacles. 



an extremely short and inconspicuous manubrium: sur- 

 rounding it are four long delicate processes, the oral arms 



