THE WHEEL-ANIMALCULE. 75 



(indicated by the colour, pi. xn, fig. 3) are seen passing 

 down to the stomach ; and at the constriction, or neck, 

 the particles may be traced in a continuous line from 

 the mouth to the internal cavities. The motion of the 

 rotators is voluntary : it can be instantly arrested, and 

 the organs drawn out of sight, and again protruded, at 

 the will of the animal. When the wheels are drawn 

 in, while the body remains extended, and its trunk pro- 

 jecting, they appear like two flat semi-elliptical disks, 

 immediately above the jaws, (pi. xn, fig. 4, b, b). 



An individual fixed by its tail, and having its body 

 much contracted, is shewn in pi. xn, fig. 7. 



The Rotifer is oviparous, and eggs in progressive 

 stages of development may generally be seen within the 

 body. A young one just escaping from the egg is re- 

 presented in pi. XH, fig. 5. The increase of this species 

 is in a ratio almost incredible. Ehrenberg has ascer- 

 tained, by direct observation, that from a single indi- 

 vidual a million may be produced by the tenth day, 

 four millions by the eleventh, sixteen millions by the 

 eighteenth, and so on. 



Such is the organisation of the Rotifer, as seen 

 under a good defining power. The mode of obtain- 

 ing these animalcules, and the varied appearances, and 

 diversified shapes and attitudes which they assume, are 



