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is termed a popular or qui tam action, because it is brought by a person qui tam pro domino rege quam pro se ipso sequitur. A suit by an informer must be brought within a year of the offence, unless a specific time is prescribed by the statute. The term informer is also used of an accomplice in crime who turns what is called “king’s evidence” (see Accomplice). In Scotland, informer is the term applied to the party who, in criminal proceedings, sets the lord advocate in motion.

INFUSORIA, the name given by Bütschli (following O. F. Ledermüller, 1763) to a group of Protozoa. The name arose from the procedure adopted by the older microscopists to obtain animalcules. Infusions of most varied organic substances were prepared (hay and pepper being perhaps the favourite ones), the method of obtaining them including maceration and decoction, as well as infusion in the strict sense; they were then allowed to decompose in the air, so that various living beings developed therein. As classified by C. G. Ehrenberg in his monumental Infusionstierchen als volkommene Organismen, they included (1) Desmids, Diatoms and Schizomycetes, now regarded as essentially Plant Protista or Protophytes; (2) Sarcodina (excluding Foraminifera, as well as Radiolaria, which were only as yet known by their skeletons, and termed Polycystina), and (3) Rotifers, as well as (4) Flagellates and Infusoria in our present sense. F. Dujardin in his Histoire des zoophytes (1841) gave nearly as liberal an interpretation to the name; while C. T. Van Siebold (1845) narrowed it to its present limits save for the admission of several Flagellate families. O. Bütschli limited the group by removing the Flagellata, Dinoflagellata and Cystoflagellata (q.v.) under the name of “Mastigophora” proposed earlier by R. M. Diesing (1865). We now define it thus:—Protozoa bounded by a permanent plasmic pellicle and consequently of definite form, never using pseudopodia for locomotion or ingestion, provided (at least in the young state) with numerous cilia or organs derived from cilia and equipped with a double nuclear apparatus: the larger (mega-) nucleus usually dividing by constriction, and disappearing during conjugation: the smaller (micro-) nucleus (sometimes multiple) dividing by mitosis, and entering into conjugation and giving rise to the cycle of nuclei both large and small of the race succeeding conjugation.

EB1911 Infusoria - Ciliata.jpg
Fig. i. Ciliata.

1. Opalinopsis sepiolae, Foett.: a parasitic Holotrichous mouthless Ciliate from the liver of the Squid. a, branched meganucleus; b, vacuoles (non-contractile).

2. A similar specimen treated with picrocarmine, showing a remarkably branched and twisted meganucleus (a), in place of several nuclei.

3. Anoplophrya naidos, Duj.; a mouthless Holotrichous Ciliate parasitic in the worm Nais. a, the large axial meganucleus; b, contractile vacuoles.

4. Anoplophrya prolifera, C. and L.; from the intestine of Clitellio. Remarkable for the adhesion of incomplete fission-products in a metameric series. a, meganucleus.

5. Amphileptus gigas, C. and L. (Gymnostomaceae). b, contractile vacuoles; c, trichocysts (see fig. 2); d, meganucleus; e. pharynx.

6, 7. Prorodon niveus, Ehr. (Gymnostomaceae). a, meganucleus; b, contractile vacuole; c, pharynx with horny cuticular lining.

6. The fasciculate cuticle of the pharynx isolated.

8. Trachelius ovum, Ehr. (Gymnostomaceae); showing the reticulate arrangement of the endosarc, b, contractile vacuoles; c, the cuticle-lined pharynx.

9, 10, 11, 12. Icthyophthirius multifilius, Fouquet (Gymnostomaceae). Free individual and successive stages of division to form spores. a, meganucleus; b, contractile vacuoles.

13. Didinium nasutum, Müll. (Gymnostomaceae). The pharynx is everted and has seized a Paramecium as food. a, meganucleus; b, contractile vacuole; c, everted pharynx.

14. Euplotes charon, Müll. (Hypotrichaceae); lateral view of the animal when using its great cirrhi, x, as ambulatory organs.

15. Euplotes harpa, Stein (Hypotrichaceae); h, mouth; x, cirrhi.

16. Nyctotherus cordiformis, Stein (a Heterotriceae), parasitic in the intestine of the Frog; a, meganucleus; b, contractile vacuole; c, food particle; d, anus; e, heterotrichous band of membranelles; f, g, mouth; h, pharynx; i, small cilia.

Thus defined, the Infusoria fall into two groups:—(1) Ciliata, with cilia or organs derived from cilia throughout their lives, provided with a single permanent mouth (absent in the parasitic Opalinopsidae) flush with the body or at the base of an oral depression, and taking in food by active swallowing or by ciliary action: (2) Suctoria, rarely ciliated except in the young state, and taking in their food by suction through protrusible hollow tentacles, usually numerous.

The pellicle of the Infusoria is stronger and more permanent than in many Protozoa, and sometimes assumes the character of a mail of hard plates, closely fitting; but even in this case it undergoes solution soon after death. It is continuous with a firm ectosarc, highly differentiated in the Ciliata, and in both groups free from coarse movable granules. The endosarc is semifluid and rich in granules mostly “reserve” in nature, often showing proteid or fat reactions. One or more contractile vacuoles are present in some of the marine and all the freshwater species, and open to the surface by pores of permanent position: a system of canals in the deeper layers of the ectoplasm is sometimes connected with the vacucle. The body is often provided with not-living external formations “stalk” and “theca” (or “lorica”).

The character of the nuclear apparatus excludes two groups both parasitic and mouthless: (1) the Trichonymphidae, with a single nucleus of Leidy, parasitic in Insects, especially Termites; (2) the Opalinidae, with several (often numerous) uniform nuclei, parasitic in the gut of Batrachia, &c., and producing 1-nuclear zoospores which conjugate. Both these families we unite into a group of Pseudociliata, which may be referred to the Flagellata (q.v.). Lankester in the last edition of this Encyclopaedia called attention to the doubtful position of Opalina, and Delage and Hérouard placed Trichonymphidae among Flagellates.

The theca or shell is present in some pelagic species (fig. iii. 3, 5) and in many of the attached species, notably among the Peritricha (fig. iii. 21, 22, 25, 26) and Suctoria (fig. viii. 11); and is found in some free-swimming forms (fig. iii. 3, 5): it is usually chitinous, and forms a cup into which the animal, protruded when at its utmost elongation, can retract itself. In Metacineta mystacina it has several distinct slits (pylomes) for the passage of tufts of tentacles. In Stentor it is gelatinous; and in the Dictyocystids it is beautifully latticed.

The stalk is usually solid, and expanded at the base into a disk in Suctoria. In Peritrichaceae (fig. iii. 8-22, 25, 26), the only ciliate group with a stalk, it grows for some time after its formation, and on fission two new stalks continue the old one, so as to form a branched colony (fig. iii. 18). In Vorticella (fig. iii. 11, 12, 14, &c.) the stalk is hollow and elastic, and attached to it along a spiral is a