INTRODUCTION. 23 



c. Mollusks living in chains or clusters, like the Salpa. fig. 

 135 ; or upon plant-like stems, like Flustra, [Bryo' 

 zoa.) 



IV. The department of Radiates is divided into three 

 classes : 



1. Sea-urchins, bearing spines upon the surface, [EcYui- 



odeniis^) figs. 12, 26. 



2. Jelly-fishes, (Acalejjhs,) fig. 31. 



3. Polyps, fixed like plants, and with a series of flexible 



arms around the mouth, figs. 48, 77, 143. 



The EcHiNODERMs are divided into four orders : 

 a. Sea-slugs, like biche-le-mar, [Holothurians.) 

 h. Sea-urchins, (Echini,) fig. 26. 



c. Free star- fishes, (Aster ides,) fig. 17. 



d. Star-fishes mostly attached by a stem, (Criiioids^) 



figs. 150, 151. 



The AcALEPHS include the following orders: 



a. Those furnished with vibrating hairs, by which they 



move, (CtcnophorcB.) 

 h. The Medusce, or common jell3^-fishes, (Discophora,) 



figs. 31, 142. 

 c. Those provided with aerial vesicles, (Siphoncqjlwra:.) 



The class of Polyps includes two orders. 



a. The so-called fresh- water polyps, and similar marine 



forms, with lobed tentacles, (Hydro'ids,) fig, 143. 

 h. Common polyps, like the sea-anemone and coraJ* 

 polyp, (Actiiioids,) fig. 48. 



In addition to these, there are numberless kinds of micro- 



