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 Rotifer 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 Rotifer 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 



77 



Fig. 58.— Cells of Sea- 

 mat, enlarged. 



Fig. 59.— Branching: marine Polyzoon. (Natural sizf .) 



* See the works of Hudson, Gosse.. Suleusky, Hyatt, etc 



