The Classification of Protozoa 105 



were subdivided, on the basis of number and position of openings to the 

 supposed digestive tract, into Anopisthia (with one terminal opening), 

 Enantiatreta (with an opening at each end of the body), Allotreta (with 

 a lateral opening), and Catotreta (with a ventral opening). 



Ehrenberg's basic misinterpretation of protozoan morphology was soon 

 corrected by Dujardin (9) who reached the conclusion that Infusoria are 

 simple organisms composed of a fundamental living substance, sarcode. 

 Repetition of Ehrenberg's feeding experiments indicated that the sup- 

 posedly fixed stomachs of ciliates are merely food vacuoles. Dujardin 

 divided the Infusoria into Asymmetrica and Symmetrica. The former 

 included species without visible locomotor organelles (bacteria), those 

 with pseudopodia (mostly Sarcodina, in the modern sense), those with 

 flagella, and those with cilia (about 50 genera of ciliates). The Sym.metrica 

 included the ciliate genus Coleps. 



In 1845, von Siebold (20) redefined the "Protozoa," in which Goldfuss 

 (11) had included certain coelenterates with the "Infusoria," and char- 

 acterized them as unicellular animals. Although such a characterization 

 is inadequate by modern standards, von Siebold's definition served a 

 useful purpose in stressing morphological differences between Protozoa 

 and higher animals. The Protozoa now included the Class Infusoria — the 

 Astoma, without a mouth {Opalina and the flagellates), and the Stoma- 

 toda, with a mouth (about 30 genera of ciliates) — and the Class Rhizo- 

 poda with (pseudopodia). 



Further investigation brought more recruits to the Protozoa. In 1845, 

 von Kolliker concluded that gregarines are Protozoa instead of trema- 

 todes, and this interpretation was supported by Stein in 1848. Increased 

 interest in these organisms finally led to Leuckart's erection of the 

 Sporozoa in 1879. Preliminary observations of Meyen, and the extensive 

 work of Huxley on Thalassicolla led J. Muller, in 1858, to establish the 

 Radiolaria as a subdivision of the Rhizopoda. The group Ciliata was set 

 up by Perty in 1852; the Flagellata, by Cohn in 1853; and extensive in- 

 vestigations on both groups were reported by Claparede and Lachmann 

 in 1858-1861. By the time Stein's (21) monograph was completed, the 

 Flagellata were divided into 15 families, some of which are now con- 

 sidered orders; the Ciliata, into the orders Holotricha, Heterotricha, 

 Hypotricha, and Peritricha. Stein's classification of ciliates on the basis 

 of distribution of cilia has been carried on, with modifications, into later 

 systems. 



Contemporary contributions included Haeckel's separation of the Heli- 

 ozoa from the Radiolaria, erection of the Mastigophora by Diesing, 

 the Sporozoa by Leuckart, the Myxosporidia and the Dinoflagellata by 

 Biitschli, and the Sarcosporidia by Balbiani. As a result, the classification 

 of Protozoa began to resemble more modern systems. 



Kent's monograph (14) covered the following groups: 



