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 Nymphaeas 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 Na'isas 
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 cylihdrical, black- 
ish, narrow at their base, larger at their summit, and 
spreading. 
In the Rhone, and other fresh waters in the north 
of Europe. 
