@misc{Calkins_Gary_Nathan_(1869–1943)_The_1901,
 author={Calkins, Gary Nathan (1869–1943) and Macmillan Company.},
 copyright={Public Domain},
 address={New York ;},
 address={London},
 journal={Columbia Biological Series},
 howpublished={online},
 year={1901},
 publisher={Macmillan Company},
 language={eng},
 title={The Protozoa},
 type={Text},
 URL={http://rcin.org.pl/Content/134867/PDF/WA488_169633_2019726_Calkins-The-Protozoa.pdf},
 keywords={Protozoa - historical overview, Modern classification of protozoa, Protozoa physiology some problems},
}