MANUBRIUM 



315 



through the angles to the centre of the manubrium are called 

 " perradial," while those bisecting the perradial planes and passing 

 therefore through the middle line of the fiat sides of the manu- 

 brium are called " interradial." 



The free extremity of the manubrium in many Scyphozoa is 

 provided with four triangular perradial lips, which may be 

 simple or may become bifurcated or branched, and have fre- 

 quently very elaborate 

 crenate edges beset 

 with batteries of nem- 

 atocysts. In Pelagia 

 and Chrysaora and 

 other genera these lips 

 hang down from the 

 manubrium as long, 

 ribbon - like, folded 

 bands, and according t 

 to the size of the 

 specimen may be a 

 foot or more in length, 

 or twice the diameter 

 of the disc. 



In the Ehizosto- 

 mata a peculiar modi- 

 fication of structure 

 takes place in the 

 fusion of the free 

 edges of the lips to 

 form a suture perforated by a row of small apertures, so 

 that the lips have the appearance of long cylindrical rods or 

 tubes attached to the manubrium, and then frequently called 

 the " oral arms." The oral arms may be further provided with 

 tentacles of varying size and importance. In many Ehizo- 

 stomata branched or knobbed processes project from the outer 

 side of the upper part of the oral arms. These are called the 

 " epaulettes." 



The lumen of the manubrium leads into a large cavity in the 

 disc, which is usually called the gastric cavity, and this is ex- 

 tended into four or more interradial or perradial gastric pouches. 

 The number of these pouches is usually four, but in this, as in 



Fig. 143. — Vlmaris prototypus. (7, Gonad ; /, interradial 

 canal ; M, the fringed lip of the manubrium ; P, per- 

 radial canal ; S, marginal sense-organ ; ^, tentacle. 

 X 1. (After Haeckel.) 



