DIVISION OR TYPE VIII. : PROTOZOA. 



Body composed of a single cell, the organs of the higher animals 

 being therefore absent. 



CLASS I. : INFUSORIA. 



Pbotozoa of a definite shape, the surface of which is wholly or partially- 

 covered with cilia, with definite oral and anal apertures. 



The Slipper Animalcule (Paramcecium aurelia). 



(Length about T ^ inch.) 



(With remarks on Protozoa and Infusoria in general.) 



A. Name. 



In 1675 the celebrated Dutch naturalist Van Leeuwenhoek (pro- 

 nounce " Layvenhook ") placed some pepper in a glass and covered it 

 with water. A few days after, on examining a drop of the liquid under 

 the microscope, he found, to his astonishment, a number of minute 

 animals swimming rapidly through the water. He had, in fact, dis- 

 covered the wonder- world of the minutest living organisms. Owing to 

 the fact that these animals were obtained by pouring water on all sorts 

 of vegetable, animal, and mineral substances — i.e., by making infusions 

 —they were called Infusoria, which name they retain to the present day. 



To obtain a view of these creatures, we shall proceed in exactly the 

 same manner as their discoverer. If we steep some hay in water, we 

 shall find a few days after every drop of it alive with Infusoria. The 

 whitish films on the surface especially teem with these creatures. 

 (Examine for the same purpose ponds and pools.) The commonest 

 species among these is certain to be one having the shape of the sole of 

 a shoe or slipper, and hence called the " slipper animalcule." For this 

 reason, and on account of its relatively large size, we shall here consider 

 this species as an example of the whole class. 



