THE RHIZOSTOMHLE. 



125 



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

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





Fig. 20.— Cephea ocellata (?).— A, 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 (n) ; g, one of the clavate tentacles interspersed between the oral pores. C, 

 one of the pedunculated lithocysts (j) in its notch (d) seen from below, with the 

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

 with its csecal lateral branches, g. 



by the umbrella and a floor, the brachiferous disk, suspended 

 by four pillars. In the roof the plaited genital membranes 



Fig. 21.— Cephea ocellata (?).— A, lithocyst enlarged with its hood (£) and the aboral 

 pore of the canal (c) ; rf, the notch of "the margin of the umbrella. B, the brachifer- 

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

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



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

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



