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Bible Encyclopedias
Infusoria
1911 Encyclopedia Britannica
or the name given by Biitschli (following O.F. Ledermiiller, 1763) to a group of Protozoa. The name arose 3 FIG. i. Ciliata.
1. Opalinopsis sepiolae, Foett.; a parasitic 8. holotrichous mouthless Ciliate from the liver of the Squid. a, branched meganucleus; b, vacuoles (non-contractile).
2. A similar specimen treated with picr09, carmine, showing a remarkably branched and twisted meganucleus (a), in place of several nuclei.
3. Anoplophrya naidos, Duj.; a mouthless Holotrichous Ciliate parasitic in 13. the worm Nais; X 200. 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 14. fission-products in a metameric series. a, meganucleus.
5. Amphileptus gigas, C. and L.; (Gymno vacuoles; c, trichocysts (see fig. 2); stomaceae) X too. b, contractile 15.
d, meganucleus; e, pharynx. 16.
6, 7. Prorodon niveus, Ehr.; (Gymnostomaceae); X 75. a, meganucleus; b, contractile vacuole; c, pharynx with horny cuticular lining.
6. The fasciculate cuticle of the pharynx isolated.
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 vollkommene Organis- men, they included (I) 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. Biitschli limited the group by removing the Flagellata, Dinoflagellata and Cystoflagellataunder 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 a 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 10 and giving rise to the cycle of nuclei both large and small of the race succeeding conjugation.
Thus defined, the Infusoria fall into two groups: - (I) Ciliata, with cilia or organs derived from cilia throughout their lives, provided with a 12 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 notliving 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 Herouard 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. II, 12, 14, &c.) the stalk is hollow and elastic, and attached to it along a spiral is a Trachelius ovum, Ehr. (Gymnostomaceae); X 80; showing the reticulate arrangement of the endosarc, b, contractile vacuoles; c, the cuticlelined pharynx.
0, II, 12. Icthyophthirius multifilius, Fouquet (Gymnostomaceae) X 120. Free individual and successive stages of division to form spores. a, meganucleus; b, contractile vacuoles.
Didinium nasutum, Mull.; (Gymnostomaceae); X200. The pharynx is everted and has seized a Paramecium as food. a, meganucleus; b, contractile vacuole; c, everted pharynx.
Euplotes charon, Mull., (Hypotrichaceae); lateral view of the animal when using its great cirrhi, x, as ambulatory organs.
Euplotes harpa, Stein (Hypotrichaceae); X 150. h, mouth; x, cirrhi. 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.
prolongation of the ectosarc containing a bundle of myonemes, so that by the contractions of the bundle the stalk is pulled down into a corkscrew spiral, and on the relaxation of the muscle the elasticity of the hollow stalk straightens it out.
On fission the stalk may become branched, as the solid one of Epistylis and Opercularia (fig. iii. 20); and the myoneme also in the tubular stem of Zoothaminum; or the branch-myoneme for the one offspring may be inserted laterally on that for the other in Carchesium (fig. iii. 18). In several tubicolous Peritrichaceae there is some arrangement for closing their tubes. In Thuricola (fig. iii. 25-26) there is a valve which opens by the pressure of the animal on its protrusion, and closes automatically by elasticity on retraction. In Lagenophrys the animal adheres to the cup a little below the opening, so that its withdrawal closes the cup: at the adherent part the body mass is hardened, and so differentiated as to suggest the frame of the mouth of a purse. In Pyxicola (fig. iii. 21-22) the animal bears some way down the body a hardened shield (" operculum ") which closes the mouth of the shell on retraction.
The cytoplasm of the Infusoria is very susceptible to injuries; and when cut or torn, unless the pellicle contracts rapidly to enclose the wounded surface, the substance of the body swells up, becoming frothy, with bubbles which rapidly enlarge and finally burst; the cell thus disintegrates, leaving only a few granules to mark where it was. This phenomenon, observed by Dujardin, is called " diffluence." The contractile vacuole appears to be one of the means by which diffluence is avoided in cells with no strong wall to resist the 1, Surface view of Paramecium, showing the disposition of the cilia in longitudinal rows.
2, a, mega-; b, micro-nucleus; c, junction of ectoand endosarc; D, pellicle; E, endosarc; f, cilia (much too numerous and crowded); g, trichocysts; g', same with thread; h, discharged; i, pharynx, its undulating membrane not shown; k, absorption of water in excess: for after growing in size for some time, its walls contract suddenly, and its contents are expelled to the outside by a pore, which is, like the anus, usually invisible, but permanent in position. The contractile vacuole may be single or multiple; it may receive the contents of a canal, or of a system of canals, which only become visible at the moment of the contraction of the vacuole (fig. ii. 4-7), giving liquid time to accumulate in them, or when the vacuole is acting sluggishly or imperfectly, as in the approach of asphyxia (fig. ii. 3). Besides this function, since the system passes a large quantity of water from without through the substance of the cell, it must needs act as a means of respiration and excretion. In all Peritrichaceae it opens to the vestibule, and in some of them it discharges through an intervening reservoir, curiously recalling the arrangements in the Flagellate Euglenaceae.
The nuclear apparatus consists of two parts, the meganucleus, and the micronucleus or micronuclei (fig. iii. 17 d, iv. 1). The meganucleus alone regarded and described as " the nucleus " by older observers is always single, subject to a few reservations. It is most frequently oval, and then is indented by the micronucleus; but it may be lobed, the lobes lying far apart and connected by a slender bridge or moniliform, or horseshoe-shaped (Peritrichaceae). It often contains darker inclusions, like nucleoles.
It has been shown, more especially by Gruber, that many Ciliata are multinucleate, and do not possess merely a single meganucleus and a micronucleus. In Oxytricha the nuclei are large and numerous (about forty), scattered through the protoplasm, whilst in other cases the nucleus is so finely divided as to appear like a powder diffused uniformly through the medullary protoplasm (Trachelocerca). Carmine staining, after treatment with absolute alcohol, has led to this remarkable discovery. The condition described by Foettinger in his Opalinopsis (fig. i. 1, 2) is an example of this pulverization of the nucleus. The condition of pulverization had led in some cases to a total failure to detect any nucleus in the living animal, and it was only by the use of reagents that the actual state of the case was revealed. Before fission, whatever be its habitual character, it condenses, becomes oval, and divides by constriction; and though it usually is then fibrillated, only in a few cases does it approach the typical mitotic condition. The micronucleus described by older writers as the " nucleolus " or " paranucleus " (" endoplastule " of Huxley), may be single or multiple. When the meganucleus is bilobed there are always two micronuclei, and at least one is found next to every enlargement of the moniliform meganucleus. In the fission of the Infusoria, every micronucleus divides by a true mitotic process, during which, however, its wall remains intact. From their relative sizes the meganucleus would appear to discharge during cell-life, exclusively, the functions of the nucleus in ordinary cells. Since in conjugation, however, the meganucleus degenerates and is in great part either digested or excreted as waste matter, while the new nuclear apparatus in both exconjugates arises, as we shall see, from a conjugation-nucleus of exclusively micronuclear origin, we infer that the micronucleus has for its function the carrying on of the nuclear functions of the race from one fission cycle to the next from which the meganucleus is excluded.
Fission is the ordinary mode of reproduction in the Infusoria, and is usually transverse, but oblique in Stentor, &c., as in Flagellata, longitudinal in Peritrichaceae; in some cases it is always more or less unequal owing to the differentiation of the body, and consequently it must be followed by a regeneration of the missing organs in either daughter-cell. In some cases it becomes very uneven, affording every transition to budding, which process assumes especial importance in the Suctoria. Multiple fission (brood-formation or sporulation) is exceptional in Infusoria, and when it occurs the broods rarely exceed four or eight - another difference from Flagellata. The nuclear processes during conjugation suggest the phylogenetic loss of a process of multiple fission into active gametes. As noted, in fission the meganucleus divides by direct constriction; each micronucleus by a mode of mitosis. The process of fission is subject in its activity to the influences of nutrition and temperature, slackening as the food supply becomes inadequate or as the temperature recedes from the optimum for the process. Moreover, if the descendants of a single animal be raised, it is found that the rapidity of fission, other conditions being the same, varies periodically, undergoing periods of depression, which may be followed by either (I) spontaneous recovery, (2) recovery under stimulating food, (3) recovery through conjugation, or (4) the death of the cycle, which would have ensued if 2 or 3 had been omitted at an earlier stage, but which ultimately seems inevitable, even the induction of conjugation failing to restore it. These physiological conditions were first studied by E. Maupas, librarian to the city of Algiers, in his pioneering work in the later 'eighties, and have been confirmed and extended by later observers, among whom we may especially cite G. N. Calkins.
Syngamy, usually termed conjugation or " karyogamy," is of exceptional character in the majority of this group - the Peritrichaceae alone evincing an approximation to the usual typical process of the permanent fusion of two cells (pairing-cells or gametes), cytoplasm to cytoplasm, nucleus to nucleus, to form a new cell (coupled cell, zygote).
This process was elucidated by E. Maupas in 1889, and his results, eagerly questioned and repeatedly tested, have been confirmed in every fact and in every generalization of importance.
Previously all that had been definitely made out was that under certain undetermined conditions a fit of pairing two and two occurred among the animals of the same species in a culture or in a locality in the open; that after a union prolonged over hours, and sometimes even days, the mates separated; that during the union the meganucleus underwent changes of a degenerative character; and that the micronucleus underwent repeated divisions, and that from the offspring of the micronuclei the new nuclear apparatus was evolved for each mate. Maupas discovered the biological conditions leading to conjugation: (1) the presence of individuals belonging to distinct stocks; (2) their belonging to a generation sufficiently removed from previous conjugation, but not too far removed therefrom; (3) a deficiency of food. He also showed that during conjugation a " migratory " nucleus, the offspring of the divisions of the micronucleus, passes from either mate to the other, while its sister nucleus remains " stationary "; and that reciprocal fusion of the migratory nucleus of the one mate with the stationary nucleus of the other takes place to form a zygote nucleus in either mate; and that from these zygote nuclei in each by division, at least two nuclei are formed, the one of which enlarges to form a meganucleus, while the other remains small as the first micronucleus of the new reorganized animal, which now separates as an " exconjugate " (fig. iv). Moreover, if pairing be prevented, or be not induced, the individuals produced by successive fissions become gradually weaker, their nuclear apparatus degenerates, and finally they cannot be induced food granules collecting into a bolus; 1, m, n, o, food vacuoles, their contents being digested as they pass in the endosarc along the path indicated by the arrows.
3, Outline showing contractile vacuoles in commencing diastole, surrounded by five afferent canals.
4-7 Successive stages of diastole of contractile vacuole.
under suitable conditions to pair normally, so that the cycle becomes extinct by senile decay. In Peritrichaceae the gametes are of unequal sizes (fig. iii. II, 12), the smaller being formed by brood fissions (4 or 8); syngamy is here permanent, not temporary, the smaller (male) being absorbed into the body of the larger (female); and there are only two nuclei that pair. Thus we have a derived binary sexual process, comparable to that of ordinary bisexual organisms.
