44 



ZOOLOGY. 



their internal organs can readily be seen through the skint, 

 ■while they are so minute, being from one fortieth to tliree 

 hundredths of ;ui inch in length (f tof 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 montlis to such a degree that little if any moist- 

 ure is left in the body, tliey may be revived and become 

 active. Professor Owen has observed tlie revivification of 

 a liotifer after having been kept for four years in dry 

 sand. 



Their body is often broad and fiat, divided into a few 

 segments of unequal size. They perform their rapid move- 

 ments by means of two ciliated flajis, one on each side of 

 the head, and wliich 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. — Poltzoa {Moss Animals). 



General Characters of the Polyzoans. — Tlie Polyzoa, 

 though not usually met with in fresh water, are among 



Fig 40 — fVIK of ^ea- Fia, ^7 — Branchinp: marine Polrzoon. (Natural size t 

 mat, enlaitred. 



See Ihe works of Hudson, (iossc, buleusky, IJ3 all, etc. 



