54 
ZOOLOGY, 
their internal organs can readily be seen through the skin, 
while they are so minute, being from one fortieth to three 
hundredths of an inch in length (f to f mm.), that high 
powers of the microscope are needed in studying them. 
They are of special interest from the fact that after being 
dried for months to such a degree that little if any moist- 
ure is left in the body, they may be revived and become 
active. Professor Owen has observed the revivification of 
a liotifer after having been kept for four years in dry 
sand. 
Their body is often broad and flat, divided into a few 
segments of unequal size. They perform their rapid move- 
ments by means of two ciliated flaps, one on each side of 
the head, and which in motion resemble wheels, whence 
their name^, wheel-animalcules. By means of the rotatory 
movements of the hairs on the edges of the flaps the micro- 
scopic Kotifer is whirled rapidly around.* 
Class IV. — Polyzoa {Moss Animals). 
General Characters of the Polyzoans. — The Polyzoa, 
though not usually met with in fresh water, are among 
Fig. 58.— Cells of Sea- Fig. 59.— Branching marine Polyzoon. (Natural size.) 
mat, enlarged. 
See the works of Hudson, Gosse, Salensky, Hyatt, etc. 
