INTROD UCTION 15 



kel, 1862, 1866), Mastigophora (Diesing, 1865). Of Suctoria, 

 Stein failed to see the real nature (1849), but his two mono- 

 graphs on Ciliata and Mastigophora (1854, 1859-1883) contain 

 concise descriptions and excellent illustrations of numerous 

 species, several of which are inserted in the present work. In- 

 deed, we owe to him much of the classification of the Ciliata 

 which is most commonly adopted at present. 



Haeckel (1873), who went a step further than Siebold and 

 distinguished between Protozoa and Metazoa, devoted ten 

 years to his study of Radiolaria, especially those of the Chal- 

 lenger collection, and described in his celebrated monographs 

 more than 4000 species. 



In 1879 the first comprehensive monograph on the Protozoa 

 of North America was put forward by Leidy under the title of 

 "Freshwater Rhizopods of North America," which showed the 

 wide distribution of many known forms of Europe and revealed 

 a number of new and interesting forms. This work was followed 

 by Stokes' "The Fresh-water Infusoria of the United States," 

 which appeared in 1888. Butschli (1880) established Sarcodina 

 and made an excellent contribution to the taxonomy of the then- 

 known species of Protozoa, which is still considered as one of the 

 most important works on general protozoology. The painstak- 

 ing researches by Maupas, on the conjugation of ciliates, cor- 

 rected erroneous interpretation of the phenomenon observed by 

 Balbiani some thirty years before and gave impetus to a re- 

 newed cytological study of Protozoa. The variety in form and 

 structure of the protozoan nuclei became the subject of intensive 

 studies by several cytologists. Weismann (1881) put into words 

 the immortality of the Protozoa. Schaudinn contributed much 

 toward the cytological and developmental studies of Protozoa. 



In the first year of the present century. Calkins in the United 

 States and Doflein in Germany wrote modern textbooks on pro- 

 tozoology dealing with the biology as well as the taxonomy. 

 Calkins initiated the so-called isolation pedigree culture of 

 ciliates in order to study the physiology of conjugation and 

 other phenomena connected with the life history of the ciliates. 

 The application of this method has been wide. 



Today the Protozoa are more and more intensively studied 

 from both the biological and the parasitological sides, and im- 



