General Description of the Protista and of Paramecium
It is the aim of this chapter to describe briefly the nature of the material that will be dealt with in the rest of this book.
The term protozoa (which today includes only the single-celled animals) was coined by Goldfuss in 1820.1 Goldfuss included some metazoa as well as singlecelled animals in his protozoa. Haeckel2 classified all organisms into three groups: plants, animals, and the single-celled organisms, or Protista. Later Haeckel3 revised his system and made it explicit that the single-celled protozoa were included in the Protista. Protists have often been considered by biologists to be the first living things existing on this planet, from which protozoa and multicellular animals and plants have evolved. In former times, university courses in biology started with brief descriptions of the protozoans, amoeba and Paramecium, with the implication that they were simple, unicellular organisms and were at the first stage of evolution toward higher multicellular animals and plants. Now we recognize DNA as the indispensable component of nuclei, and it is held to be the foundation of genetics. Most textbooks on biology now begin with the structure and function of DNA.