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CILIATA

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Originally appearing in Volume V14, Page 563 of the 1911 Encyclopedia Britannica.
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CILIATA.—The Ciliate Infusoria represent the highest type of Protozoa. They are distinctly animal in function, and the Gymnostomaceae are active predaceous beings preying on other Infusoria or Flagellates. Some possess shells (fig. iii. 3, 5, 21, 22, 25, 26), most have a distinct swallowing apparatus, and in Dysteria there is a complex jaw—or tooth-apparatus, which needs new investigation. In the active Ciliata we find locomotive organs of most varied kinds: tail-springs, cirrhi for crawling and darting, cilia and mernbraneilae for continuous swimming in the open or gliding over surfaces or waltzing on the substratum (Trichodina, fig. iii. 8) or for eddying in wild turns through the water (Strombidium, Tintinnus, Halteria). Their forms offer a most interesting variety, and the flexibility of many adds to their easy grace of movement, especially where the front of the body is produced and elongated like the neck of a swan (Amphileptus, fig. iii. 5; Lacrymaria). The cytoplasm is very highly differentiated : especially the ectoplasm or ectosarc. This has always a distinct elastic " pellicle " or limiting layer, in a few cases hard, or even with local hardenings that affect the disposition of a coat of mail (Coleps) or a pair of valves (Dysteria); but is usually only marked into a rhomboidal network by intersecting depressions, with the cilia occupying the centres of the areas or meshes defined. The cytoplasm within is distinctly alveolated, and frequently contains tubular alveoli running along the length of the animal. Between these are dense fibrous thickenings, which from their double refraction, from their arrangement, and from their shortening in contracted animals are regarded as of muscular function and termed " myonemes." Other threads running alongside of these, and not shortening but becoming wavy in the general contraction have been described in a few species as neuronemes " and as possessing a nervous, conducting character. On this level, too, lie the dot-like granules at the bases of the cilia, which farm definite groups in the case of such organs as are composed of fused cilia; in the deeper part of the ectoplasm the vacuoles or alveoli are more numerous, and reserve granules are also found; here too exist the canals, sometimes developed into a complex net-work, ,i which open into the contractile vacuole. The cilia themselves have a stiffer basal part, probably strengthened by an axial rod, and a distal flexible lash; when cilia are united by the outer plasmatic layer, they form (I) Cirrhi," stiff and either hook-like and pointed at the end, or brush-like, with a frayed apex; (2) membranelles, flattened organs composed of a number of cilia fused side by side, sometimes on a single row, some-times on two rows approximated at either end so as to form a narrow oval, the membranelle thus being hollow; (3) the oral " undulating membrane," merely a very elongated membranelle whose base may extend over a length nearly equal to the length of the animal; such membranes are present in the mouth oral depression and pharynx of all but Gymnostomaceae, and aid in ingestion; a second or third may be present, and behave like active lips; (:f) in Peritrichaceae the cilia of the peristomial wreath are united below into a continuous undulating membrane, forming a spiral of more than one turn, and fray out distally into a fringe; (5) the dorsal cilia of Hypotrichaceae are slender and motionless, its cessation, separation; probably sensory. clotted lines indicate Embedded in the ectosarc of many fission; the spaces Ciliates are trichocysts, little elon- lettered 1-7 successive gated sacs at right angles to the stages in the process; surface, with a fine hair-like process the clear circles projecting. On irritation these elon- cate functionless nuclei gate into strong prominent threads, which degenerate. often with a more or less barb-like head, and may be ejected altogether from the body. Those over the surface of the body appear to be protective; but in the Gymnostomaceae specially strong ones surround the mouth. They can be injected into the prey pursued, and appear to have a distinctly poisonous effect on it. They are combined also into defensive batteries in the Gymnostome Loxophyllum. They are absent from most Heterotrichaceae and Hypotrichaceae, and from Peritrichaceae, except for a zone round the collar of the peristome. The openings of the body are the mouth, absent in a few parasital species (Opalinopsis, fig. i. 1, 2), the anus and the pore of the contractile vacuole. The mouth is easily recognizable; in the most primitive forms of the Gymnostomaceae and some other groups, it is terminal, but it passes further and further back in more modified species, thereby defining a ventral, and correspondingly a dorsal surface; it usually lies on the left side. The anus is usuallyonly visible during excretion, though its position is permanent; in a few genera it is always visible (e.g. Nyctotherus, fig. i. i6). The pore of the contractile vacuole might be described in the same terms. The endoplasm has also an alveolar structure, and containsbesijes large food-vacuoles or digestive vacuoles, and shows movements of rotation within the ectoplasm. from which, however, it is not usually distinctly bounded. In Ophryoscolex and Didinium (fig, i. 13) a permanent cavity traverses it from mouth to anus. Ingestion of food is of the same character in all the Hymenostomata. The ciliary current drives a powerful stream into the mouth, which impinges against the endosarc, carrying with it the food particles; these adhere and accumulate to form a pellet, which ultimately is pushed by an apparently sudden action into the substance of the endosarc which closes behind it (fig. ii. 2). In some Q b C From Calkins' Protozoa, by permission of the Macmillan Company, N.Y. of the Aspirotrichaceae accessory undulating membranes play the part of lips, and there is a closer approximation to true deglutition. The mouth is rarely terminal, more frequently at the bottom of a depression, the " vestibule," which may be prolonged into a slender canal, sometimes called the " pharynx " or " oral tube," ciliated as well as provided with a membrane, and extending deep down into the body in many Peritrichaceae. In Spirostomaceae the " adoral wreath " of membranelles encloses more or less completely an anterior part of the body, the " peristome," within which lies the vestibule. This area may be depressed, truncate, convex or produced into a short obconical disk or into one or more lobes, or finally form a funnel, or a twisted spiral like a paper cone. In most Peritrichaceae a collar-like rim surrounds the peristome, and marks out a gutter from which the vestibule opens; the peristome can be retracted, and the collar close over it. This rim forms a deep permanent spiral funnel in Spirochona (fig. iii. Io). Movements of Ciliata.—H. S. Jennings has made a very detailed study of these movements, which resemble those of most minute free-swimming organisms. The following account applies practically to all active " Infusoria " in the widest sense. The position of the free-swimming Infusoria, like that of Rotifers and other small swimming animals, is with the front end of the body inclined out- ward to the axis of advance, constantly changing its azimuth while pre- A serving its angle constant or nearly so; if advance were ignored the body would thus rotate FIG. vii.—Diagram of a mode of progression so as to trace out of a Ciliate like Paramecium; m, mouth and a cone, with the Pharynx; the straight line A, B, represents the hinder end at the axis of progression described by the posterior apex, and the front end, and the spiral line the curve described by describing the base. the anterior end ; the clear circles are the On any irritation, contractile vacuoles on the dorsal side. (I) the motion is arrested, (2) the animal reverses its cilia and swims backwards, (3) it swerves outwards away from the axis so' as to make a larger angle with it, and (a.) then swims forwards along a new axis of progression, to which it is inclined at the same angle as to the previous axis (figs. vi., vii.). In this way it alters its axis of progression when it finds itself under conditions of stirhulation. Thus a Paramecium coming into a region relatively too cold, too hot, or too poor in CO2 or in nutriment, alters its direction of swimming; in this way individuals come to assemble in crowds where food is abundant, or even where there is a slight excess of CO2. This reaction may lead to fatal results; if a solution of corrosive sublimate (Mercuric chloride) diffuses towards the hinder end of the animal faster than it progresses, the stimulus affecting the hinder end first, the axis of progression is altered so as to bring the From Zoology. M, Old meganucleus under-going disintegration. m, Micronucleus. \, migratory, and S, Stationary pairing--nucleus. M', M', the new meganuclei, and m', The new micronuclei in the products of the first fission of each of the ex-conjugates; the continu ous vertical line indicates period of fusion, animal after a few changes into a region where the solution is strong enough to kill it. This " motile reaction," first noted by H. S. Jennings, is the explanation of the general reactions of minute swimming anirnals to most stimuli of whatever character, including light ; the practical working out is, as he terms it, a method of " trial and error." The action, however, of a current of electricity is distinctly and immediately directive; but such a stimulus is not to be found in nature. The motile reaction in the Hypotrichaceae which crawl or dart in a straight line is somewhat different, the swerve being a simple turn to the right hand—i.e. away from the mouth. Parasitism in the Infusoria is by no means so important as among Flagellates. Ichthyophlhirius alone causes epidemics among Fishes, and Balantidium tali has been observed in intestinal disease in Man. The Isotricheae, among Aspirotrichaceae and the Ophryoscolecidae among Heterotrichaceae are found in abundance in the stomachs of Ruminants, and are believed to play a part in the digestion of cellulose, and thus to he rather commensals than parasites. A large number of attached species are epizoic commensals, some very indifferent in choice of their host, others particular not only in the species they infest, but also in the special organs to which they adhere. This is notably the case with the shelled Peritrichaceae. Lichnophora and Trichodina (fig. iii. 8, 9) among Peritrichaceae are capable of locomotion by their permanent posterior wreath or of attaching themselves by the sucker which surrounds it; Kerona polyporum glides habitually over the body of Hydra, as does Trichodina pediculus. Several Suctoria are endoparasitic in Ciliata, and their occurrence led to the view that they represented stages in the life-history of these. Again, we find in the endosarc of certain Ciliates green nucleated cells, which have a cellulose envelope and multiply by fission inside or outside the animal. They are symbiotic Algae, or possibly the resting state of a Chlamydomonadine Flagellate (Carteria?), and have received the name Zoochlorella. They are of constant occurrence in Paramecium bursaria, frequent in Stentor polymorphus and S. igneus, and Ophrydium versatile, and a few other species, which become infected by swallowing them. Classification. Order I.—Section A.—Gymnostomaceae. Mouth habitually closed; swallowing an active process; cilia (or membranelles) uniform, usually distributed evenly over the body; form variable, sometimes of circular transverse section. Section B.—Trichostomata. Mouth permanently open against the endosarc, provided with i or 2 undulating membranes often prolonged into an inturned pharynx; ingestion by action of oral ciliary apparatus. Order 2.—Subsection (a).—Aspirotrichaceae. Cilia nearly uni- form, not associated with cirrhi or membranelles, nor forming a peristomial wreath. Form usually flattened, mouth unilateral. (N.B.—Orders 1, 2 are sometimes united into the single order Holotrichaceae.) Subsection (b).—Spirotricha. Wreath of distinct membranelles—or of cilia fused at the base—enclosing a peristomial area and leading into the mouth. §§ i.—Wreath of separate membranelles. 1-der 3.—Heterotrichaceae; body covered with fine uniform cilia, usually circular in transverse section. Order 4.—Oligotrichaceae; body covering partial or wholly absent; transverse section usually circular. Jrder 5.—Hypotrichaceae; body flattened; body cilia represented chiefly by stiff cirrhi in ventral rows, and fine motion-less dorsal sensory hairs. Order 6.—§§ ii.—Peritrichaceae. Peristomial ciliary wreath, spiral, of cilia united at the base; posterior wreath circular of long membranelles; body circular in section, cylindrical, taper, or bell-shaped. Illustrative Genera (selected). 1. Gymnostomaceae. (a) Ciliation general or not confined to one surface. Coleps Ehr., with pellicle locally hardened into mailed plates; Trachelocerca Ehr. ; Prorodon Ehr. (fig. i. 6, 7) ; Trachelius Ehr., with branching endosarc (fig. i. 8) ; Lacrymaria Ehr. (fig. i. 5), body produced into a long neck with terminal mouth surrounded by offensive trichocysts; Dileptus Duj., of similar form, but anterior process, blind, preoral; Ichthyophlhirius Fouquet (fig. i. 9-12), cilia represented by two girdles of membranellae; Didinium St. (fig. i. 13), cilia in tufts, surface with numerous tentacles each with a strong terminal trichocyst; Actinobolus Stein, body with one adoral tentacle; Ileonema Stokes. (b) Cilia confined to dorsal surface. Chilodon Ehr.; Loxodes Ehr., body flattened, ciliated on one side only, endosarc as in Trachelius; Dysteria Huxley, with the dorsal surface hardened and hinged along the median line into a bivalve shell, ciliated only on ventral surface, with a protrusible foot-like process, and a complex pharyngeal armature. (c) Cilia restricted to a single equatorial girdle, strong (probably membranelles) ; dfesodiniuni, mouth 4-lobed. 2. Aspirotrichaceae. Paramecium Hill (fig. ii. 1-3) ; Ophryoglena Ehr.; Colpoda 0. F. Muller; Colpidium St.; Lembus Cohn, with posterior strong cilium for springing; Leucophrys St.; Urocentrum Kitsch, hare, with polar and equatorial zones and a posterior tuft of long cilia; Opalinopsis Foetlinger (fig. i. I, 2); Anoplophyra St. (fig. i. 3, 4). (The last two parasitic mouthless genera are placed here doubtfully.) 3. Heterotrichaceae. (a) Wreath spiral; Stentor Oken. (fig. iii. 2), oval when free, trumpet-shaped when attached by pseudopods at apex, and then often secreting a gelatinous tube; Blepharisma Pcrty, sometimes parasitic in Heliozoa; Spirostomum Ehr., cylindrical, up to 1" in length; (b) Wreath straight, often oblique; Nyctotherus Leidy, parasitic anus always visible; Balantidium Cl. and L., parasitic (B. coil in man) ; Bursaria, O.F.M., hollowed into an oval pouch, with the wreath inside. 4. Oligotrichaeceae. Tintinnus Schranck (fig. iii. 3) ; Trichodinopsis Cl. and L. ; . Codonella Haeck. (fig. iii. 5) ; Strombidiunt Cl. and L. (fig. iii. 4), including Torqualella Lank. (fig. iii. 6, 7), according to Butschli; Haheria Duj., with an equatorial girdle of stiff bristle-like cilia; Caenomorpha Perty (fig. iii. 23, 24); Ophryoscolex St., with straight digestive cavity, and visible anus, parasitic in Ruminants. 5. Hypotrichaceae. Stylonychia Ehr.; Oxytricha Ehr. ; Euplotes Ehr. (fig. i. 14, IS); Kerona Ehr. (epizoic on Hydra). 6. Peritrichaceae. 1. Peristomial wreath projecting when expanded above a circular contractile collar-like rim. (a) Fam. Urceolaridae: posterior wreath permanently present around sucker-like base. Trichodina Ehr. (fig. iii. 8, 9), epizoic on Hydra; Lichnophora Cl. and L.; Cyclochaeta Hatchett Jackson ; Gerda Cl. and L.; Scyphidia Duj. (b) Fam. Vorticellidae =Bell Animalcules: posterior wreath temporarily present, shed after fixation. Subfam. 1. Vorticellinae animals naked. (i.) Solitary; Vorticella Linn. (fig. iii. 11-17), stalk hollow with spiral muscle; Pyxidium S. Kent, stalk non-contractile. (ii.) Forming colonies by budding on a branched stalk: Carchesium Ehr., hollow branches and muscles discontinuous; Zoothamnium. Ehr., branched hollow stem and muscle continuous through colony; Epistylis Ehr., stalk rigid—(the animal body in these three genera has the same characters as Vorticella)—Campanella Goldf., stalked like Epistylis, wreath of many turns (nematocysts sometimes present) (fig. iii. 19) ; Opercularia, stalk of Epistylis, disk supporting wreath obconical, collar very high (fig. iii. 20). Subfam. 2. Vaginicolinae; body enclosed in a firm theca: Vaginicola Lam., shell simple, sessile; Thuricola St. Wright, shell sessile, with a valve opening inwards (fig. iii. 25-26) ; Cothurnia Ehr., shell stalked, simple; Pyxicola S. Kent, shell stalked, closed by an infraperistomial opercular thickening on the body (fig. iii, 21-22). Subfam. 3. Shells gelatinous; those of the colony aggregates into a floating spheroidal mass several inches in diameter Ophrydium Bory, O. versatile contains Zoochlorella, which secretes oxygen, and the gas-bubbles float the colonies like green lumps o'. jelly. 2. Peristomial wreath, not protrusible, surrounded by a very high usually spiral collar. Fam. Spirochonina. Spirochona St. (fig. iii. 1o); Kentrochona Rompel; both genera epizoic on gills, &c., of small Crustacea. SucToRuA.—These are distinguished from Ciliata by their possession of hollow tentacles (one only in Rhyncheta, fig. viii. 1, and Urnula) through which they ingest food, and by not possessing cilia, except in the young stage. Fission approximately equal is very rare. Usually it is unequal, or if nearly equal one of the halves remains attached, and the other, as an embryo or gemmule, develops cilia and swims off to attach itself else-where; Sphaerophrya (fig. viii. 2-6) alone, often occurring as an endoparasite in Ciliata, may be free, tentaculate and unattached. The ectosarc is usually provided with a firm pellicle which shows a peculiar radiate " milling " in optical section, so fine that its true nature is difficult to make out; it may be due to radial rods, regularly imbedded, or may be the expression of radial vacuoles. The tentacles vary in many respects, but are always retractile. They are tubes covered by an extension of the pellicle; this is invaginated into the body round the base of the tentacle as a sheath, and then evaginated to form the outer layer of the tentacle itself, over which it is frequently raised into a spiral ridge, which may be traced down into the part sunk and ensheathed within the body: in Choanophrya, where the tentacles are largest, the pellicle is further continued into the interior of the tentacle. The tentacles are always pierced by a central canal opening at the apex, which may be (1) enlarged into a terminal capitate sucker, (2) slightly flared, (3) truncate and closed in the resting state to become widely opened into a funnel, or (4) pointed. The tentacles are always capable of being waved from side to side, or turned in a definite direction for the reception or prehension of food; in Rhyncheta, the movements of the long single tentacle recall those of an elephant's trunk, only they are more extensive and more varied. In the majority of cases the food consists of Ciliata : and the contents of the prey may be seen passing down the canal of the sucker beyond where it becomes free from the general surface. In Choanophrya the food appears to consist of the debris of the prey of the carnivorous host (Cyclops), which is sucked into the wide funnel-shaped mouths of the tentacles—by what mechanism is unknown. The endosarc is full of food-granules and reserve-granules (oil, colouring matter and proteid). The meganucleus and the micronucleus are both usually single, but in Dendrosoma (fig. viii. 2o), of which the body is branched, and the meganucleus with it, there are numerous micronuclei. In most cases the micronucleus has not been recorded, though from the similarity of conjugation, and its presence in most cases of fission and budding that have been accurately described, we may infer that it is always present. In unequal fission the meganucleus sends a process into the bud, while the micronucleus divides as in Ciliata. The bud may be nearly equal to the remains of the original-animal, or much smaller, and in that case a depression surrounds it which may deepen so as to form a brood-cavity, either communicating by a mere " birth-pore " with the outside or entirely closed. In some cases the budding is multiple (fig. viii. 8), and a large number of buds are formed and liberated at the same time. In all cases the bud escapes without tentacles, and possesses a characteristic supply of cilia, whose arrangement is constant for the species. In some cases an adult may withdraw its tentacles, moult its pellicle and develop an equipment of cilia and swim away: this is the case with Dendrocometes, parasitic on Gammarus, when its host moults. The numerous species of Suctoria, often so abundant on various species of Cyclops, are not found on the other fresh-water Copepoda, Diaptomus and Canthocamptus, belonging indeed to other families. Again, these Suctoria affect different positions, those found on the antennae not being present on the mouth parts; the ventral part of the thorax has another set; and the inside of the pleural fold another. Rhyncheta occupies the front of the " couplers " or median down-growths uniting the coxopodites of the swimming legs, and Choanophrya settles in the immediate neighbourhood of the mouth, preferably on the epistoma, labrum and metastomatic region, but also on the adoral appendages and in rare cases extends, when the settlement is extensive, to the bases of the two pairs of antennae; while distinct species of Podophrya settle on the antennae, the front of the thorax and the inside of the pleural folds. Dendrocometes is common on the gills of the freshwater shrimp (Amphipod) Gammarus and Stylocometes on the gills and gill-covers of the Isopod Asellus, the water-slater. The independence of the Acinetaria was threatened by the erroneous view of Stein that they were phases in the life-history of Vorticellidae. Small parasitic forms (Sphaerophrya) were also regarded erroneously as the " acinetiform young " of Ciliata. They now must be regarded as an extreme modification of the Protozoon series, in which the differentiation of organs in a unicellular animal reaches its highest point. Principal Genera. 1. Unstalked simple forms. Urnula Cl. and L., permanently ciliate; Rhyncheta Zenker (fig. viii. 1), on the limb couplers of Cyclops; Sphaerophrya Cl. and L. (fig. viii. 2-6, 12), endoparasitic in Ciliata and formerly taken for embryos thereof, never attached; Trichophrya CI. and L. (fig. viii. 7), of similar habits, but temporarily attached, sessile. 2. Stalked simple forms; Podophrya Ehr. (fig. viii. to, 13, 16), tentacles all knobbed or flared; Ephelota Strethill Wright, tentacles all pointed; Hemiophrya S. Kent (fig. viii. 8, 9, 14), tentacles of both kinds; Choanophrya Hartog, tentacles thick, truncate, very retractile, when expanded opening into funnels for aspiration of floating prey, never for attachment—epizoic on antero-ventral parts of Cyclops. 3. Cupped forms; Solenophrya Cl. and L., cup sessile; Acineta Ehr., cup stalked; Acinetopsis Biitschli, like Acineta, but the cu flattened, closed distally with only slit-like apertures (" pylomes for the bundles of tentacles; Podocyathus, like Acineta, but with pointed as well as knobbed tentacles. 4. Tentacles in bundles at the tips of one or more processes or branches of the body. Ophryodendron Cl. and L., tentaculiferous process single (fig. viii. 21); Dendrocometes Stein (fig. viii. 15), body rounded, processes repeatedly branched, epizoic on gills of Gammarus pulex; Dendrosoma Ehr. (fig. viii. 17-20), body freely branched from a basal attached stolon, meganucleus branching with the body. 14, Hemiophrya benedenii, Fraip. ; the suctorial tentacles retracted. 15, Dendrocometes paradoxus, Stein. Parasitic on Gammarus pulex; captured prey. 16, Asinle tentacle of Podophrya. R. Hertwig. 17-20, Dendrosoma radians, Ehr.: -17, free-swimming ciliated embryo. 18, Earliest I, Rhyncheta cyclopum, Zenker; only a single tentacle and that suctorial; epizoic on Cyclops. 2, Sphaerophrya urostylae, Mau-pas; normal adult; parasitic in Ciliate Urostyla. 3, The same dividing by trans-verse fission, the anterior moiety with temporarily developed cilia. 4, 5, 6, Sphaerophrya slentorea, Maupas. Parasitic in Stentor, and at one time mistaken for its young. 7, Trichophrya epistylidis, Cl. and L. 8, Hemiophrya gemmipara, Hertwig. Example with six buds, into each of which a branch of the meganucleus a is extended. 9, The same species, showing the two kinds of tentacles (the suctorial and the pointed), and two contractile vacuoles b. lo, Ciliated embryo of Podophrya steinii, Cl. and L. 11, A cineta grandis, Saville Kent ; showing pedunculated cup, and animal with two bunches of entirely suctorial tentacles. 12, Sphaerophrya magna, Mau-pas. It has seized with its tentacles, and is in the act of sucking out the juices of six examples of the Ciliate Colpoda parvifrons. 13, Podophrya elongata, Cl. and L. fixed condition of the embryo. 19, Later stage, a single tentaculiferous process now developed. 20, Adult colony; c, en-closed ciliated embryos; d, branching stolon; e, more minute reproductive (?) bodies. 21, Ophryodendron pedicellatum, Hincks. a ks Rhisopodes (1858—1861); F. von Stein, Der Organismus der 'nfusionstiere (1859—1883);; W. Saville Kent, A Manual of the Infusoria, including a description of all known Flagellate, Ciliate and Tentaculiferous Protozoa (188o-1882). (c) Infusoria, as limited by Biitschli. O. Biitschli, Bronn's Tierreich, vol. i. Protozoa, pt. 3 Infusoria (1887–1889), the most complete work existing, but without specific diagnoses; S. J. Hickson, " The Infusoria " in Lankester's Treatise on Zoology, vol. i. fasc. 2 (1903), a general account, well illustrated, with a diagnosis of all genera. See also Delage and Herouard, Traite de Zoologie concrete, vol. i. " La Cellule et les Protozoaires " (1896), with an illustrated conspectus of the genera; E. Maupas, Recherches experimentales sur la multiplication des Infusoires cilies," Arch. zool. exp. vi. (1888); and " Le Rajeunissement karyogornique chez les Cilies," ib. vii. (1889); R. Sand, Etude monographique sur le groupe des Infusoires tentaculiferes (Suctoria), (1899), with diagnoses of species; A. Lang, Lehrb. der vergleich. A natomie der wirbellosen Tiere, vol. i. " Protozoa " (1901) (a view of comparative anatomy, physiology and bionomics) ; Marcus Hartog, " Protozoa," in Cambridge Natural History, i. (1906); H. S. Jennings, Contributions to the Study of the Behaviour of Lower Organisms (1904) ; G. N. Calkins, " Studies on the Life History of Protozoa " (Life cycle of Paramecium), I. Arch. Entw. xv. (1902), II. Arch. Prot. i. (1902), III. Biol. Bull. iii. (1902), IV. J. Exp. Zool. i. (1904). Numerous papers dealing especially with advances in structural knowledge have appeared in the Archiv fur Protistenkunde, founded by F. Schaudinn in 1902. (M. HA.)
End of Article: CILIATA
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