ECHINODERMATA. 
257 
Class III. —Ctenophora. 
The Ctenophora (as the Pleuro- 
brachia , Cestum , and Beroe) 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¬ 
paratus and a definite nervous sys¬ 
tem. 
robrachia pileus) ; natural 
size. 
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 ali- 
e 
Pig. 210_ Forms of Echinoderms, from radiate to annnlose type: a , Criuoids; b , 
Ophiurans; c, Star-fish; d, Echini; e, Holothurians. 
mentary canal, completely shut off from the body-cavity, 
and having both oral and anal apertures; a water-vascular 
17 
