12 PROTOZOOLOGY 



fera, which he considered "microscopical cephalopods." In 1828 

 Ehrenberg began publishing his observations on Protozoa and in 

 1838 he summarized his contributions in Die Infusionsthicrchen als 

 vollkommene Organismen, in which he diagnosed genera and species 

 so well that many of them still hold good. Ehrenberg excluded Rota- 

 toria and Cercaria from Infusoria. Through the studies of Ehrenberg 

 the number of known Protozoa increased greatly; he, however, pro- 

 posed the term "Polygastricha," under which he placed Mastigo- 

 phora, Rhizopoda, Ciliata, Suctoria, desmids, etc., since he believed 

 that the food vacuoles present in them were stomachs. This hypothe- 

 sis became immediately the center of controversy, which incidentally, 

 together with the then-propounded cell theory and improvements in 

 microscopy, stimulated researches on Protozoa. 



Dujardin (1835) took pains in studying the protoplasm of various 

 Protozoa and found it alike in all. He named it sarcode. In 1841 he 

 published an extensive monograph of various Protozoa which came 

 under his observations. The term Rhizopoda was coined by this 

 investigator. The commonly used term protoplasm was employed by 

 Purkinje (1840) in the same sense as it is used today. The Protozoa 

 was given a distinct definition by Siebold in 1845, as follows: "Die 

 Thiere, in welchen die verschiedenen Systeme der Organe nicht 

 scharf ausgeschieden sind, und deren unregelmassige Form und ein- 

 fache Organization sich auf eine Zelle reduzieren lassen." Siebold 

 subdivided Protozoa into Infusoria and Rhizopoda. The sharp differ- 

 entiation of Protozoa as a group certainly inspired numerous micros- 

 copists. As a result, several students brought forward various group 

 names, such as Radiolaria (J. Muller, 1858), Ciliata (Perty, 1852), 

 Flagellata (Cohn, 1853), Suctoria (Claparede and Lachmann, 1858), 

 Heliozoa, Protista (Haeckel, 1862, 1866), Mastigophora (Diesing, 

 1865), etc. Of Suctoria, Stein failed to see the real nature (1849), but 

 his two monographs on Ciliata and Mastigophora (1854, 1859-1883) 

 contain concise descriptions and excellent illustrations of numerous 

 species. Haeckel who went a step further than Siebold by distinguish- 

 ing between Protozoa and Metazoa, devoted 10 years to his study 

 of Radiolaria, especially those of the Challenger collection, and de- 

 scribed 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 Fresh- 

 water Rhizopods of North America, which showed the wide distribu- 

 tion 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. 



