INFUSORIA. 617 



Order IV. 



Polypi, with the mouth furnished with hairs. These 

 vibrate rapidly, and produce currents in the water. Very 

 minute, and require the aid of the microscope in their exa- 

 mination. 



1st Tribe. 



Oral hairs in tufts. This includes the genera Folliculi- 

 na, Brachionus, Furcularia, Urceolaria, Vorticella and 

 Tubicolaria. 



2d Tribe. 



Vibrating hairs not collected in tufts, as Rattulius, Tri 

 chocerca and Vaginicola. 



Class IV, INFUSORIA. 



The animals of this last class exhibit the greatest simpli- 

 city of parts. They have no visible mouth, stomach, or 

 internal vessels. They possess, however, the power of 

 swimming about in the water, by the action of parts, the 

 structure of which the microscope cannot help us to unfold. 

 They appear to propagate by buds, eggs, or spontaneous 

 division. They are usually met with in infusions of vege- 

 table and animal substances, both in fresh and salt water. 

 They are too minute for the eye to perceive their forms, 

 and require the aid of the microscope. The work of MUL- 

 LER on the " Animalcula Infusoria," is the storehouse 

 from which naturalists derive their descriptions of all the 

 genera of this class, and of the last order of the preceding. 

 LAMARK has contributed a good deal towards distributing 

 the genera into convenient groups, but a great deal yet re- 

 mains to be done, even with the materials which MULLER 

 has furnished. 



Order I. 



The animals of this order have always some external or- 

 gans, as cuticular processes or hairs. Two of the genera 

 VOL. u. R r 



