LESSON 32.] NUTRITION IN THE ECHINODERMA. 



109 



the circular vessel (184, d) passing round the margin, and by placing 

 the living Medusa in sea water tinged with indigo, the stomach (18P, 

 c), the radiating vessels (184, b, 5), and the circular marginal canal 

 (184. d), are soon found to be filled with the blue coloring matter, 



Fie. 183. FIG. 184. 



Cetonia aurita. 



Cetonia aurita. 



while the rest of the animal remains colorless. The free margin of 

 the mantle is fringed with a row of minute tentacula, which appear 

 to be highly sensitive, and in constant motion ; the organs of vision 

 (according to Ehrenberg) are placed in the slight depressions around 

 the free edge of the disc (e, 183 ; /, 184). 



LESSON XXXII. 



ORGANS OF NUTRITION IN THE ECHINODERMA. 



527. The bodies of Star- 

 fishes, Echini, &c., are more 

 or less covered with spines 

 (Fig. 185), and hence the 

 name of the class, which is 

 formed from echinus, a spine 

 and derma, skin ; frequently 

 they are called the prickly- 

 skinned animals. 



528. The digestive ap- 

 paratus in the Star-fishes, Echinus. 



and its immediate allies (Euryale, Ophiura, or brittle stars, Asterias, 



