142 ZOOLOGY. 



SUB-KINGDOM VII. Protozoa. 

 CLASS 1. Infusoria. 



207. If a quantity of boiling water be poured upon a 

 few stalks of hay, or other vegetable matter, and allowed 

 to stand for a few days : if a drop of this infusion be then 

 taken and examined by a microscope, it will be found to 

 contain a multitude of minute creatures, moving about 

 with great agility. A like result will be produced by 

 placing the vegetable substance in a glass of water, and 

 exposing it for a few days to the rays of the sun. These 

 animals have been called Infusoria, because they were 

 first met with in vegetable infusions. The early ob- 

 servers included the Eotifera in this class ; but, as these 

 are much more highly developed animals than the In- 

 fusoria, they have now been placed in the sub-kingdom 

 Annuloida. 



208. The animals produced at first are called monads, 

 and are extremely small. " If arranged side by side 

 in contact with each other like the beads of a necklace 

 twelve thousand of them could be placed within the 

 length of a single inch." If the infusion be allowed to 

 remain for some time longer, fresh forms will be produced, 

 some of them considerably larger than the monads. 



The Infusoria are not confined to infusions of animal 

 or vegetable matter, as they abound in stagnant water 

 everywhere, and are even found in the sea. 



They may be defined as Protozoa, which possess a per- 

 manent mouth, and short gullet, which terminates in the 

 central mass of sarcode. Their bodies consist of three dis- 

 tinct layers, the outer one being generally furnished with 

 cilia. They differ from the Ehizopoda, also, in not having 

 the power of protruding pseudopodia. 



209. Some of the Infusoria are free swimming, others 

 are attached to aquatic plants by a slender stalk. Para- 

 mcEcium (Gr. parameTces, oblong) may be taken as an 



