104 The Classification of Protozoa 



relatives, the taxonomist encounters organisms which range from typical 

 flagellates (of which many are apochlorotic and some are holozoic) to 

 filamentous algae with temporary flagellate stages. In assigning algal 

 flagellates to the Phylum Protozoa and leaving their close relatives with 

 the botanists, protozoologists obviously have made arbitrary decisions 

 which are more indicative of taxonomic convenience than of biological 

 relationships. The dual taxonomic role of the slime-molds as Sarcodina 

 and Fungi indicates another point at which the boundaries of the Phylum 

 Protozoa are obscure. Comparable uncertainty exists at the lower levels 

 of protozoan taxonomy, and there are instances in which orders appar- 

 ently overlap to such a degree that the exact positions of certain genera 

 are still uncertain. In modern taxonomic practice, it is no novelty for a 

 particular genus or family to be moved from one subphylum, class, or 

 order to another. Old orders have sometimes disappeared completely, in 

 suppressions or amalgamations, and new orders have been carved out of 

 older groups. The continued erection of new genera and species is paral- 

 leled to some extent by the suppression of old names. In other words, a 

 certain amount of taxonomic confusion extends throughout much of the 

 Phylum Protozoa. This confusion does not indicate chaos. Instead, it is 

 the result of continued activity in a field still seriously handicapped by 

 the lack of adequate information. 



TAXONOMY PRIOR TO 1900 



Although current classifications leave much room for improvement, 

 there has been tren;iendous progress since Gesner described one of the 

 Foraminiferida as a mollusc in 1565. Protozoa apparently were first sep- 

 arated from other animalcules in 1752, when John Hill placed some of 

 them in his group of Gymnia (animalcules without external organs). In 

 1786, O. F. Miiller (17) erected the Infusoria (including about 150 species 

 of Protozoa) as a subdivision of the worms, and divided the group into 

 species with, and those without, visible locomotor organelles. 



Ehrenberg's (10) more extensive monograph included descriptions of 

 about 350 species from original observations, but an important part of 

 his taxonomic system was based upon a liberal interpretation of the 

 Infusoria as complete organisms. On the basis of feeding experiments with 

 pigments, Ehrenberg concluded that a digestive system is characteristic 

 of ciliates. "Polygastric" types were believed to have a mouth, oesophagus, 

 many stomachs, a spiral intestine, an anus, and possibly a pancreas. The 

 Infusoria were separated into Anentera (without a digestive tract) and 

 Enter odela (with a digestive tract). The Anentera were subdivided into 

 Gymnia (no visible appendages), including about 30 genera of flagellates; 

 Pseudopoda (with pseudopodia), including Amoeba, Arcella, and certain 

 Suctorea; and Epitricha (with cilia), including a few ciliates and several 

 dinoflagellates. Additional ciliates were placed in the Enterodela which 



