The chief investigators of this group have been Huxley, Cienkowski, Allman, Bütschli, and G. Pouchet, while Ischikawa and Doflein have elucidated the conjugation.

CHAPTER VI

PROTOZOA (CONTINUED): INFUSORIA (CILIATA AND SUCTORIA)

IV. Infusoria.

Complex Protozoa, never holophytic save by symbiosis with plant commensals, never amoeboid, with at some period numerous short cilia, of definite outline, with a double nuclear apparatus consisting of a large meganucleus and a small micronucleus (or several),[[149]] the latter alone taking part in conjugation (karyogamy), and giving rise after conjugation to the new nuclear apparatus.

The name Infusoria was formerly applied to the majority of the Protozoa, and included even the Rotifers. For the word signifies organisms found in "infusions" of organic materials, including macerations. Such were made with the most varied ingredients, pepper and hay being perhaps the favourites. They were left for varying periods exposed to the air, to allow the organisms to develop therein, and were then examined under the microscope.[[150]] With the progress of our knowledge, group after group was split off from the old assemblage until only the ciliate or flagellate forms were left. The recognition of the claims of the Flagellates to independent treatment left the group more natural;[[151]] while it was enlarged by the admission of the Acinetans (Suctoria), which had for some time been regarded as a division of the Rhizopoda.

I. Ciliata

Infusoria, with a mouth, and cilia by which they move and feed; usually with undulating membranes, membranellae, cirrhi, or some of these. Genera about 144: 27 exclusively marine, 50 common to both sea and fresh water, 27 parasitic on or in Metazoa, the rest fresh water. Species about 500.

We divide the Ciliata thus:[[152]]—

(I.) Mouth habitually closed, opening by retraction of its circular or slit-like margin; cilia uniform Order 1. Gymnostomaceae.
Lacrymaria, Ehrb.; Loxodes, Ehrb.; Loxophyllum, Duj.; Lionotus, Wrez.; Trachelius, Schrank; Amphileptus, Ehrb.; Actinobolus, St.; Didinium, St.; Scaphiodon, St; Dysteria, Huxl.; Coleps, Nitzsch.; Dileptus, Duj.; Ileonema, Stokes; Mesodinium, St.
(II.) Mouth permanently open, usually equipped with one or more undulating membranes, receiving food by ciliary action (Trichostomata, Bütschli)
(a) Cilia nearly uniform, usually extending over the whole body, without any special adoral wreath of long cilia or membranellae; mouth with one or two undulating membranes at its margin or extending into the short pharynx. Order 2. Aspirotrichaceae.
Paramecium, Hill; Colpoda, O. F. Müll.; Colpidium, St.; Leucophrys, Ehrb.; Cyclidium, Cl. and L.; Lembadion, Perty; Cinetochilum, Perty; Pleuronema, Duj.; Ancistrum, Maup.; Glaucoma, Ehrb.; Uronema, Duj.; Lembus, Cohn; Urocentrum, Nitzsch; Icthyophtheirius, Fouquet.
(b) Strong cilia or membranellae forming an adoral wreath, and bounding a more or less enclosed area, the "peristome," at one point of which the mouth lies.
(i.) Body more or less equally covered with fine cilia; adoral wreath an open spiral Order 3. Heterotrichaceae
Spirostomum, Ehrb.; Bursaria, O. F. Müll.; Stentor, Oken; Folliculina, Lamk.; Conchophtheirus, St.; Balantidium, Cl. and L.; Nyctotherus, Leidy; Metopus, Cl. and L.; Caenomorpha, Perty; Discomorpha, Levander; Blepharisma, Perty.
(ii.) Body cilia limited in distribution or absent; peristome anterior, nearly circular, sinistrorse. Order 4. Oligotrichaceae.
Halteria, Duj.; Maryna, Gruber; Tintinnus, Schrank; Dictyocystis, Ehrb.; Strombidium, Cl. and L. (= Torquatella, Lank.).
(iii.) Peristome extending backwards along the ventral face, which alone is provided with motile cirrhi, etc.; dorsal cilia fine, motionless. Order 5. Hypotrichaceae.

Stylonychia, Ehrb.; Kerona, O. F. Müll.; Oxytricha, Ehrb.; Euplotes, Ehrb.; Stichotricha, Perty; Schizotricha, Gruber.
(iv.) Body cilia reduced to a posterior girdle, or temporarily or permanently absent; peristome anterior, nearly circular, edged by the adoral wreath,[[153]] bounded by a gutter edged by an elevated rim or collar. Order 6. Peritrichaceae.
Lichnophora, Cl.; Trichodina, Ehrb.; Vorticella, L.; Zoothamnium, Bory; Carchesium, Ehrb.; Epistylis, Ehrb.; Opercularia, Lamk.; Vaginicola, Lamk.; Pyxicola, Kent; Cothurnia, Ehrb.; Scyphidia, Lachmann; Ophrydium, Bory; Spirochona, St.