PHYLUM I. 



PROTOZOA.* (SINGLE-CELLED ANIMALS.) 



The Protozoa are minute, aquatic animals which consist each of a single 

 cell. The body, like any other animal cell, is a mass of protoplasm con- 

 taining one or more nuclei. Distinct organs, in the ordinary sense, are not 

 present, but certain specialized structures are usually found in the body 

 which perform certain special functions. The Protozoa perform all the 



Fig. 1 Fig. 2 



Fig. 1 Amoeba Umax (Conn). Fig. 2 Amceba proteus (Conn); cv, contractile 



vacuole; ec, ectosarc; en, entosarc; ex, excreta; n, nucleus; 



p, pseudopodium. 



essential functions which characterize the 'animal body. The superficial 

 layer of the protoplasmic body is usually hyaline and distinct and is called 

 the ectosarc (Fig. 2). It secretes in most forms a cuticula or even a hard 

 shell which gives the body definite form. In the simplest cases, locomotion 

 is accomplished by the thrusting out of projections called pseudopodia 

 (Fig. 2) in the direction of movement. In the highest forms, however, cilia 



* See "Protozoa," by O. Biitschli. Bronn's "Klassen u. Ord. des Thierreichs," 

 Vol. I, 1880-1889. "A List of the Protozoa and Rotifers Found in the Illinois River," 

 etc., by A. Hempel, Bull. 111. St. Lab., Vol. 5, p. 301, 1898. "A Report on the Pro- 

 tozoa of Lake Erie," etc., by H. S. Jennings, Bull. U. S. Fish. Com., 1899, p. 105. 

 "The Protozoa," by G. N. Calkins, 1901. "Marine Protozoa of Woods Hole," by same, 

 Bull. U. S. Fish. Com., 1901, p. 413. "The Protozoa of the Fresh Waters of 

 Connecticut," by H. W. Conn, Bull. No. 2, State Geol. and Nat. Hist. Survey. "The 

 Protozoa of Iowa," by C. H. Edmondson, Proc. Acad. Sci., Davenport, 1906. "The 

 Protozoa of Sandusky Bay," by F. L. Landacre, Proc. Ohio St. Acad. Sci., Vol. 4, 

 p. 421, 1908 (containing a full bibliography). "Protozoology," by G. N. Calkins, 

 1909, "Lehrbuch der Protozoenkunde," by F. Doflein, 3d Ed., 1911. "The Protozoan 

 Parasites of Domestic Animals," by H. Crawley, Circ. 194, Bur. An. Ind., Dep. of 

 Ag., 1912. 



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