CHAPTER XV 

 THE PARAMECIUM AND ITS ALLIES 



PABAMECIUM 1 belongs to the Protozoa, 2 the lowest 

 group of animals, characterized by the fact that the body 

 contains no specialized tissues and organs, but is made 

 up of a single cell, and is usually microscopic. Protozoa 

 live in water or in moist situations. 3 



The Infusoria were unknown to man until the latter 

 half of the seventeenth century, when a Dutch naturalist 

 named Leeuwenhoek, by means of the newly invented 

 compound microscope, studied and described several kinds 

 which he had found in standing water and called animal- 

 cules or water insects. As the microscope became per- 

 fected, progress was made in the study of these organisms, 

 but even in the early half of our century several eminent 

 zoologists maintained that the Infusoria possessed digestive, 

 neural, haemal, and reproductive organs. The proper 

 structure of the Infusoria has been generally recognized 

 only within the last fifty years. 



The conceptions formerly entertained concerning the 

 origin of Infusoria were as erroneous as those relating to 

 their internal structure. These erroneous conceptions 

 were an inheritance from a time when even scientific men 



1 Trapa/i^/c^s, somewhat long. 



2 TT/OWTOJ, earliest ; fa>ov, animal. 



8 Keys to the four classes of Protozoa and to the orders of Infusoria will 

 be found in the Appendix to this Chapter, page 229. 



222 



