98 CLASS I.— ORDER III. 



NAISA. 



A FIXED Polypidom; stem slender, membra- 

 nous, frequently ramified, terminated, as are also its 

 branches, by a polypus, whose body can wholly enter 

 within the stem, and whose mouth is surrounded by a 

 row of tentacula, generally ciliated. 



These Polypidoms are found in various situations ; 

 some place themselves beneath the large leaves of 

 the Nymphasas which float on the surface of running- 

 waters ; others prefer stones that shelter them from the 

 light. 



They seldom exceed three centimetres in height, 

 but are generally much smaller. 



It is usually in clear running streams that the Naisas 

 are to be found ; the number of their species is small, 

 probably because they are not much known, and the 

 few that are known are confined to Europe ; although 

 there is no reason to suppose they do not exist in the 

 equatorial regions, as these little beings, concealed 

 beneath the leaves of aquatic plants, have been over- 

 looked by the naturalists who have visited those 

 distant countries. 



CREEPING. 



1. Naisa repens. Tubes nearly cylindrical, black- 

 ish, narrow at their base, larger at their summit, and 

 spreading. 



In the Rhone, and other fresh waters in the north 

 of Europe. 



