INTRODUCTION 13 



Butschli (1880-1889) 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 gen- 

 eral protozoology. The painstaking researches by Maupas, on the 

 conjugation of ciliates, corrected erroneous interpretation of the 

 phenomenon observed by Balbiani some 30 years before and gave 

 impetus to a renewed cytological study of Protozoa. The variety in 

 form and structure of the protozoan nuclei became the subject of in- 

 tensive studies by several cytologists. Weismann 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 Dofiein in Germany wrote modern textbooks of protozo- 

 ology dealing with the biology as well as the taxonomy. Jennings de- 

 voted his time for nearly 40 years to the study of genetics of Pro- 

 tozoa. Recent development of bacteria-free culture technique in cer- 

 tain flagellates and ciliates, has brought to light important informa- 

 tion regarding the nutritional requirements and metabolism of these 

 organisms. 



Today the Protozoa are more and more intensively and exten- 

 sively studied from both the biological and the parasitological sides, 

 and important contributions appear continuously. Since all parasitic 

 Protozoa appear to have originated in free-living forms, the com- 

 prehension of the morphology, physiology, and development of the 

 latter group is obviously fundamentally important for a thorough 

 understanding of the former group. 



Compared with the advancement of our knowledge on free-living 

 Protozoa, that on parasitic forms has been very slow. This is to be ex- 

 pected, of course, since the vast majority of them are so minute that 

 the discovery of their presence has been made possible only through 

 improvements in the microscope and in technique. 



Here again Leeuwenhoek seems to have been the first to observe 

 a parasitic protozoan, for he observed, according to Dobell (1932), in 

 the fall of 1674, the oocysts of the coccidian Eimeria stiedae, in the 

 contents of the gall bladder of an old rabbit; in 1681, Giardia intes- 

 tinalis in his own diarrhceic stools; and in 1683, Opalina and Nycto- 

 therus in the gut contents of frogs. The oral Trichomonas of man was 

 observed by O. F. Miiller (1773) who named it Cercaria tenax (Do- 

 bell, 1939). There is no record of anyone having seen Protozoa living 

 in other organisms, until 1828, when Dufour's account of the grega- 

 rine from the intestine of coleopterous insects appeared. Some ten 

 years later, Hake rediscovered the oocysts of Eimeria stiedae. A 



