CHAPTER XVII 

 THE ANIMAL KINGDOM 



The animal kingdom may be subdivided into 17 phyla, only 

 about 10 or 12 of which are ordinarily studied by the beginning 

 student. The present account includes all the phyla and usually 

 the major subdivisions, but detailed descriptions are confined 

 to animals commonly studied in the laboratory. Since there is 

 still uncertainty as to the proper systematic position of some 

 animals, the grouping followed here must be regarded as a 

 tentative one and not necessarily the ultimate arrangement. In 

 citing examples of animals typical of a phylum or its subdivisions, 

 there is given either the scientific name, consisting of the name 

 of the genus followed by that of the species, or the generic name 

 alone. A common name is mentioned also where a common name 

 is in use.* 



PHYLUM 1— PROTOZOA 



Knowledge of the existence of the group of animals now known 

 as Protozoa dates from 1674, when they were observed and 

 described by the Dutch microscopist, van Leeuwenhoek, whose 

 pioneer work with the microscope led to the discovery of many 

 organisms of minute size. The term Protozoa was applied to 

 the group by Goldfus in 1820. Protozoa (first or primitive 

 animals) may be defined as single-celled animals living singly, 

 or in colonies in which the members are attached to one another. 

 The apparent simplicity of their organization is largely a matter 

 of minuteness in size of the individual organisms. Visible 

 evidence of differentiation consists in the presence of organelles, 

 which to all intents and purposes are functionally comparable to 



* In the preparation of this chapter numerous sources were drawn upon, 

 particularly the following: H. S. Pratt: "A Manual of the Common Inverte- 

 brate Animals," Philadelphia; H. S. Pratt: "A Manual of Land and Fresh- 

 water Vertebrate Animals," Philadelphia; H. H. Wilder: "The Pedigree of 

 the Human Race," New York; C. L. Metcalf and W. P. Flint: "Destructive 

 and Useful Insects," New York. 



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