ZOOLOGY. 269 



ORDER V. 



INFUSORIA. 



The subjects of this order are all exceedingly minute, being - 

 for the most part only discoverable by the Microscope ; 

 they are found in stagnant waters, vegetable infusions, and 

 are generally known hj the terni Animalcules. They are 

 divisible into three families : * with external organs : **with- 

 ont external organs, flattened : *** without external organs, 

 round. 



1. Brachionus. Bodj/ contractile, covered with a shell, 



and furnished at the head with ciliated rotatory organs. 



2. Vorticella. Body contractile, naked, and furnished with 



ciliated rotatory organs ; this genus is divided into three 

 families ; * anirnal affixed on a stem or pedicle ; ** 

 animal tailed ; *** animal without stem or tail. 



Most of this genus are so minute, as not to be discover- 

 able without the aid of a lens. 



3. Trichoda. Animal minute, pellucid, hairy or horned ; 



there are two families in this genus, the one hairy, the 

 other with horn-like processes. They are all micro- 

 scopic objects, and invisible without the assistance of 

 ' glasses. 



4. Cercaria. Aiiimal invisible to the naked eye ; pellucid 



and tailed. 



