LUMINOUS ECHINODEBMS. 29 



CHAPTER IV. 



LUMINOUS ECHIITODERMS. 



IN the fourth grand branch of the animal kingdom, numer- 

 ous creations are known which exhibit luminosity.. The* 

 Echinoderms, as they are termed, are not well known to those' 

 who are not familiar with the seashore. To those who visit' 

 the marine beaches, one of the first objects that is met cast' 

 up by the tide, either fresh from its ocean bed among the. 

 rocks, or lying cast up high and dry amongst the vast masses 

 of kelp, algse, and other marine debris, is a sea-urchin, — so' 

 called for want of a better name, although the spines with 

 which it is powerfully armed give good color to the nomen- 

 clature. The term Echinoderm is used to express all the; 

 kinds, as they have spines on the skin. As the arrangement 

 of this division of Nature suggests, the creatures which are 

 embraced here are next farther advanced in perfection of 

 structure from the third, which includes the corals, and sea- 

 anemones. The animals are of most varied shape, exteriorly 

 most unlike each other, yet internally possessing a structure 

 each characteristic of the type. The sea-stars, forms quite 

 as common as the sea-urchins which we first mentioned, aie 

 closely alike in structure, though so different in shape. Yet 

 another form is seen in the celebrated trepang, which is 

 dried, smoked, and sold to the Chinese for food, — a great 

 luxury to them. Small species are found- on our coast.; 



