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- Ft» 
paratus and a definite nervous sys- ptleu * ); 
tern. 
A Ctenophore ( Pleu- 
natural 
Subkingdom III. —Echinodermata. 
The Echinoderms, as Star-fishes and Sea-urchins, are 
distinguished by the possession of a distinct nervous sys¬ 
tem (a ring around the mouth); an alimentary canal, com- 
Fig. 210.—Forms of Echinoderms, from radiate to annnlose type: a, Crinoids; 6, 
Ophiurans; c, Star-fish; d, Echini; e, Holothurians. 
pletely shut off from the body-cavity, and having both 
oral and anal apertures; a water-vascular system of circu- 
17 
