98 THE VITAL FUNCTIONS. 



Ehrenberg forms of these the tribe of Cycloccela, 

 of which the Vorticella citrina, and the Stentor 

 jiolymorphus, are examples. Thus do we dis- 

 cover the same diversity in the structure of the 

 digestive organs of the several races of these 

 diminutive beings, as is found in the other classes 

 of animals. 



The Ilydatina setita, one of the largest of the 

 Infusoria, was found by Ehrenberg to possess a 

 highly developed structure with respect to many 

 systems of organs, which we should never have 

 expected to meet with in animals situated so low 

 in the scale. As connected with the nutritive 

 functions, it may here be mentioned that the 

 head of this animalcule is provided with a regular 

 apparatus for mastication, consisting of serrated 

 jaws ; each having from two to six teeth. These 

 jaws are seen actively opening and shutting when 

 the animal is taking its food, which consists of 

 particles brought within reach of the mouth by 

 means of currents excited by the motions of the 

 cilia. 



Such are the simple forms assumed by the 

 organs of assimilation among the lowest orders 

 of the animal creation ; namely, digesting cavities, 

 whence proceed various canals, which form a 

 system for the transmission of the prepared nou- 

 rishment to different parts ; but all these cavities 

 and canals being simply hollowed out of the 

 solid substance of the body. As we ascend a 



