THE WHEEL-ANIMALCULE. 73 



the upper extremity of the body there is a protuberance, 

 or trunk, on which are two round red eyes placed on 

 ganglions, and a soft eye-speck. On each side this 

 trunk is a rotator, consisting of a semicircular cup 

 fringed with strong cilia: these organs are commonly 

 called the wheels. There is a respiratory tube, for the 

 free passage of water to the interior. The lower ex- 

 tremity of the body is furnished with a tail having six 

 points when expanded. The upper part of the aliment- 

 ary canal has a constriction or pharynx, which is sur- 

 rounded by four hemispherical muscular masses, placed 

 opposite to each other in a crucial position ; and these 

 are very manifest when in action. The pair of jaws, 

 with teeth, are of the type figured and described in 

 p. 56, and may be distinctly seen even in the em- 

 bryo. The nature and relative situation of these se- 

 veral parts will be best understood by reference to a 

 highly magnified view, by Ehrenberg, of a Rotifer 

 with the wheels displayed, and of which pi. xu, fig. 3, 

 is a reduced figure. 



a, The trunk or proboscis on which the eyes are placed. 



i, b, The rotatory organs, or wheels. The spiral course of the eddies in- 

 duced in the water by the action of their cilia is indicated by the 

 arrows. 



c, The respiratory tube. 



