THE SCYPHOMEDUSAE 



section, with perradial angles, and in some cases provided with 

 short perradial lappets (Palephyra). In the Semostomae these 

 lappets are drawn out into long perradial oral arms (Aurelia) with 

 a median groove, often guarded by frilled edges (Pelagia) ; the 

 arms may take origin almost directly from the subumbrella, or 

 may spring from a fairly long manubrium. Very rarely each arm 

 bifurcates once (Aurosa). In both these sub-orders a crucial 



FIG. 12. 



Diagram of Cannorhiza from the subumbral aspect, the arm disc with the eight oral arms 

 having been removed. (From Haeckel.) 



mouth is placed in the centre of the manubrium between the bases 

 of the arms. In the Rhizostomae, a Semostoman stage apparently 

 occurs in the development, and is followed by an incomplete con- 

 crescence of the frilled edges of the bifurcated arms over the 

 median groove and the mouth ; thus, instead of a central mouth, 

 numerous small suctorial openings, numbering often hundreds, are 

 formed along the edges of the arm, which open by short tubes into 



