ECHINODERMATA. 



267 



Class III. — Ctenophora. 



The Ctenophora (as the Pleuro- 

 hrachia, Cestum, and JBeroe) secrete 

 no hard deposit. They are trans- 

 parent and gelatinous, swimming on 

 the ocean by means of eight comb- 

 like, ciliated bands, which work like 

 paddles. The body is not contrac- 

 tile, as in the Jelly-fishes. They are 

 considered the highest of Ccelente- 

 rates, having a complex nutritive ap-Fio.ang — a ctenophore («e«- 



1 1 u . robrachia pileus) ; natural 



paratus and a dennite nervous sys- size, 

 tem. 



Subkingdom IV. — Echinodeemata. 



The Echinoderms, as Star-fishes and Sea-urchins, are dis- 

 tinguished by the possession of a distinct nervous system (a 

 ring around the month with radiating branches); an ali- 





Fio. 210. — Forme of Echinoderms, fi'om radiate to anniilose type: li, Crinoids; 6, 

 OphiurauB ; c, Star-fish ; d, Echini ; e, Holothnrians. 



mentary canal, completely shut off from the body-cavity, 

 and having both oral and anal apertures; a water-vascular 



17 



