72 



NATURAL HISTORY. 



Fio. 69. — Two rotifers, one of which 



Brachionus) leads ;i free life; 



th e other i B, Stepkanoceros) builds 



:i tulx'. 



Ill 



head of a pin, but their transparence renders it an easy task to study their 



In the typical forms there is a circle of cilia surrounding 

 the mouth, and the rapid motion of these cilia 

 gives one the same impression as a rapidly 

 turning wheel, whence both the common and 

 the scientific names. In others the circle of 

 cilia is drawn out into lobes or slender pro- 

 cesses, as shown in Figure 69, B, while in still 

 others the cilia may be entirely lacking. 



In habits there is a considerable difference 

 among rotifers. Some live attached to some 

 submerged object, while others swim freely 

 and rapidly through the water. Many of the 

 attached forms build a protective case, which 

 most instances is gelatinous, but in one form (Melicerta) it is so pecu- 

 liar as to deserve a moment's notice. That charming writer on natural 

 history, the late Mr. Gosse, first described the way in which this case is 

 built. The continual motion of the cilia of the animal 

 drives the minute particles in the water to the mouth. 

 Here the edible portions are swallowed, while the indigest- 

 ive ones are formed into little pellets, fastened together 

 by a glutinous secretion. Then the animal bends over 

 and places this pellet on the supporting object. Again 

 and again is the process repeated, until at last, just as the 

 brick-layer erects a building, the animalcule constructs a 

 circular wall around his body. In Figure 70 but a por- 

 tion of this case is shown. 



Among the free forms of rotifers three kinds of motion 

 may be seen. Most species only swim, the motion of the 

 cilia propelling them gracefully and rapidly through the 

 Fio.70. -a tube-build- water. A few, however, progress with a looping motion 

 oKe'tube'remo^ed like a leech, while still fewer have a jumping or skipping 

 motion, which is effected by long arms which project from 

 ; he body. Etol iters are especially noticeable from their power of withstanding 

 desiccation. They may be so dried that their bodies will blow hither and 

 thither with the wind, and yet a short soaking in water will revive all of 

 their activities. This fact readily explains their presence in what are 

 apparently the most unfavorable situations, as temporary roadside pools or 

 the water in the gutters of buildings. 



