PROTOZOA. 165 



this class because the species abound in any infusion 

 of vegetable or even animal matter which is allowed 

 to putrefy. The word was formerly applied to a much 

 larger number of species than now, since many forms 

 once considered animal have been placed in the vegeta- 

 ble kingdom, as the Desmids, the Diatoms, the Volvox, 

 and many other Protophytes. The Rotifers, or wheel- 

 animalcules, also, on account of their organization, are 

 referred to the articulate type of animal life. It is pos- 

 sible that some of the Infusoria may be but larval forms 

 of higher animals. After all this pruning, however, the 

 class is still a large one, and full of interest. It is divided 

 into three orders : Ciliata, Suctoria^ and Flagellata. 



Ciliated Infusoria (ciliatd) are most numerous, and are 

 named from the cilia, or hair-like organs, round the 

 mouth, or body, of the animalcule. Cilia are not con- 

 fined to animalcules. They are found among Proto- 

 phytes, (Chap. VI, Sec. 3.) They also exist in many 

 organs of the higher animals, as in the respiratory pas- 

 sages even of man himself. They appear to be tapering 

 prolongations of bioplasm, or of formed material in con- 

 nection with bioplasm, and have a sort of waving or 

 circular motion. In the internal organs of man their 

 actions are constant, entirely without consciousness, and 

 may continue long after the death of the body. In the 

 animalcules the ciliary action is interrupted and renewed 

 in such a way as to impress an observer with the idea of 

 choice and direction. 



Vorticella, or the bell-shaped animalcule, was described 

 in Chap. I, Sec. 6, and the life-history there given may 

 serve for a representation of the entire order. 



