ECHINODERMATA. 395 



IV. POLYPI or Zoophytes; comprehending all those small, 

 gelatinous, and compound or aggregated animals which have a 

 mouth surrounded by tentacula, and conducting into a simple 

 stomach. 



V. The INFUSORIA, or those smaller beings only known 

 through the medium of the microscope, which are found in stag- 

 nant waters. The greater part of these have a gelatinous body, 

 and are destitute of viscera, though some of the species pos- 

 sess visible organs of movement and a stomach. 



CLASS X. ECHINODERMATA. 



Body suborbicular, with a coriaceous or crustaceous covering, 

 radiated) destitute of head, eyes, and articulated feet ; 

 mouth inferior, simple, or multiform ; organs of digestion 

 compound ; exterior tubes or pores for respiration. 



THE animals of this class were arranged by some of the older 

 naturalists among the testaceous Mollusca ; by others among 

 the Zoophytes ; while others considered them as allied to the 

 Crustacea. The more modern writers, however, founding their 

 divisions on the comparative structure of the animals, as well 

 as their external characters, have placed the animals of this 

 group in a separate class, Cuvier making them the first class 

 of his great division of ZOOPHYTES, or animals with prehensile 

 and retractile tentacula, and Lamarck placing them also in a 

 separate class, under the title of RADIARIA. 



In this class the radiated structure, both externally and in- 

 ternally, forms a distinctive character. The body is generally 

 orbicular, covered with a skin or a crustaceous or calcareous en- 

 velope, and often armed with tubercles or jointed and moveable 

 spines. The interior cavity is provided with distinct viscera, 

 and a kind of vascular system maintains a communication with 

 the different parts of the intestine and with the organs of respi- 

 ration. These organs consist in pores or orifices, or exterior 

 tubes for the passage of the water. The animals of this class 

 are destitute of head, eyes, and articulated feet ; their nervous 



