THE RIIIZOSTOMID^. 



125 



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

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



^ :^ 



B -,r>. 



^ \ 



#"% 



^ A- :'' 



Fig. 'HQ.—Cei^hea occUata (?).— ^, part of the umbrella, viewed from below, to Phow 

 the plaited geuital membrane ( f) and the divided attaclimeiit oi' one of i he pillars ; 

 d, place of one of the lithocysts. B, one of the oral pores (m) purrouuded by ten- 

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

 one of ihe pedunculated lithocysts {/) in its nolcli {^d) seen from below, witli the 

 oval plate from which muscular tibres(/0 take their origin ; e, the radiating canal 

 with its cajcal lateral branches, g. 



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

 by four pillars. In the roof the plaited genital membranes 



3C) na^-^ 



Fig. 2\.— Ceph€a ocellata {'t).—A, lithncyst enlarged with its hooci (A-) and the aboral 

 pore of tlie canal (c) ; rf, the notch of tiie margin of the umbrella. B, the brachiler- 

 ons disk with the.oriirins of the arms ; /", endoderm ; o. ectoderm. C, tentaculate 

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



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

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



