242 



ECHINODERMA. 



the mouth communicating id) with the tentacles, (b) with five 

 radial vessels, one for each ambulacral area, (c) with a 

 " Polian vesicle " or more than one pendent in the body 



ov.<^ 





h 



Fig. yS. — Dissection of Holoth 



The gut has been removed ; there is a bristle throtigh anus (a) and 

 cloaca (r) ; o, mouth ; 'J\ the retracted tentacles ; ^>?-, a respiratory 

 tree ; i>7', the ovary ; otf, the oviduct ; *, a bristle at genital aperture. 



cavity, (d) with a " stone canal " which usually hangs freely in 

 the body cavity, and opens into it. The radial vessels may 



uiia. (After HuMER.) 



