THE RHIZOSTOMID^. 



125 



chambers, the walls of which unite, become perforated, and 

 thus give rise to a sub-umbrellar cavity with a roof formed 



A ^.■« 



Fig. 2Q.—Cephea ocellata (?).— ^, part of the umbrella, viewed from below, to show 

 the plaited genital membrane (/) and the divided attachment of one of the pillars ; 

 d^ place of one of the lithocysts. B, one of the oral pores {m) surrounded by ten- 

 tacula (/i) ; g, one of the clavate tentacles interspersed between the oral pores. C, 

 one of the pedunculated lithocysts {i) in its notch {d) seen from below, with the 

 oval plate from which muscular fibres (h) take their origin ; e, the radiating canal 

 with its caecal lateral branches, a. 



by the umbrella and a floor, the brachiferous disJc^ suspended 

 by four pillars. In the roof the plaited genital membranes 



5a.©« 



Fig. 2i.— Cephea ocellata (?).— ^, litlioc-yst enlarged with its hood {Jc) and the aboral 

 pore of the canal (c) ; d, the notch of Ihe mararin of the umbrella. B, the brachifer- 

 ous disk with the origins of the arms : f, endoderm ; o, ectoderm. C, tentaculate 

 lip of an oral pore enlarged ; m, oral cavity ; w, nematocysts. 



are developed. The floor (Fig. 21, B) gives off" the subdivided 

 arms, the free margins of which bear the oral pores, and 



