CLASS OF THE ROTIFEBA. 



457 



composed of animated jelly, nourished by imbibition; now it 

 is no longer the simplicity of their structure which surprises 

 us, but the complication of their organization, wholly micro- 

 scopic. 



These animalcules are met 

 with in stagnant waters. Their 

 body is semi-transparent, and 

 presents traces sufficiently dis- 

 tinct of annular divisions. The 

 mouth occupies the anterior ex- 

 tremity, and on each side, or 

 even all around the orifice, may 

 generally be seen vibratile cilia, 

 the rotatory movements of which 

 are extremely remarkable. Al- 

 most always the phary nx (ar-r iere- 

 bouche) is furnished with power- 

 ful muscles, and armed with 

 lateral jaws. The digestive canal 

 is straight ; it extends from one 

 extremity of the body to another, 

 and has generally towards the 

 middle an enlargement, repre- 

 senting the stomach of these 

 small beings ; often may be seen 

 on either side of this tube, bodies 

 apparently glandular, and at its 

 posterior extremity a sort of cloaca, in which terminate the 

 oviducts. A great number of muscles have also been dis- 

 covered in these animalcules, and even a ganglionary nervous 

 system. 



587. The rotifera (Fig. 154), one species of which has 

 become celebrated by the experiments of Spallanzani on the 

 suspension of life which follows its drying up, may be taken 

 as a type of the class. Their body is elongated, and is ter- 

 minated anteriorly by two small coronoe of cilia, which, at the 

 will of the animal, are withdrawn into the interior or expanded 

 externally, and which by their vibrations produce the image of 

 two small wheels turning rapidly on their axis. They ter- 



Fig. 443. The Hydatina.* 



* Anatomy of the Hydatina, a microscopic animalcule next the Rotifera: 

 a, vibratile cilia ; b, fleshy mass surrounding the mouth and moving the 

 jaws; c, the stomach; d, the cloaca; e, the anus; /, salivary glands; g, 

 ovaria; h, the muscles. 



