116 INVERTEBRATES. 



Found fixed by their base. They are common, and are often seen 

 in immense shoals. One species of them is vulgarly known by 

 the name of sun-fish. 



The Polypes have a hollow, cylindrical, or conical "body, 

 with one extremity open, which serves for their mouth, and is 

 surrounded by a number of tentacula. The simple cavity thus 

 formed constitutes their only organ, and performs all the functions 

 of which they are capable. They seize their prey and convey it 

 to their mouths with the tentacula, and, as their bodies are gela- 

 tinous and semi-transparent, the operation of digestion may be 

 seen going on within. Many of the polypes have been celebrated 

 on account of the fact, that when one is divided into several pieces, 

 each piece becomes a distinct animal, perfect in all its parts. The 

 immense beds of coral, and the different kinds of sponge, are no- 

 thing but the habitations of infinite numbers of these little animals, 

 and are produced by their labor. 



The Antmalcules are animals still more minute, and are 

 scarcely discernible except by the assistance of the microscope. 

 Thousands of them are in this way brought to our view, of various 

 shapes, sizes, and appearances. Most of them offer to the view 

 merely a gelatinous mass, capable of an imperfect sort of motion. 

 Some, however, present appearances of a structure which might 

 give them a claim to a higher rank in the scale of beings, did not 

 their minuteness prevent a proper examination. These animals 

 are principally found in some animal and vegetable fluids and in- 

 fusions, and hence have sometimes received the name of Infusoria. 



