ECHINODERMATA. 



357 



CLASS III. Ctenophora. 



The Ctenophora, (as the Pleuro- 

 brachia, Cesium, and Beroe) secrete 

 no hard deposit. They are trans- 

 parent and gelatinous, swimming on 

 the ocean bj 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 Coelente- 

 rates, having a complex nutritive ap-Fio.209 A ctenophore (Pieu- 



, ,. . robrachia pileut) ; natural 



paratus and a dennite nervous sys- size. 

 tern. 



Subkingdom IV. ECHINODERMATA. 



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

 tinguished by the possession of a distinct nervous system (a 

 ring around the mouth with radiating branches); an all- 



Fie. 210. Forms of Echiuoderms, from radiate to annulose type: o, Crinoids; ft, 

 Ophiarans; c, Star-fish; d, Echini; , Holothurians. 



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

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



IT 



