Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/885

CILIATA.] PROTOZOA 861 flagcllata and the Rhynchoflagellata with the true Flagellata in one class. But the peculiarities of the organization of the two former groups is best emphasized by treating them as separate classes de rived from the Flagellata. Neither group leads on to the Ciliata or to any other group, but they must be regarded as forming a lateral branch of the family tree of Corticata. The relationship of Nocti- luca to Peridinium was first insisted upon by Allman, but has quite recently been put in a new light by Biitsehli, who identifies the atrial recess of Noctiluca (Fig. XXII. 20, 1} with the longitudinal furrow or groove of the Dinofiagellata, and the large and minute flagella of the former with the transverse and longitudinal flagella respectively of the latter. The superficial ridge c of Noctiluca appears to represent the continuation of the longitudinal groove. The phosphorescence of the sea, especially on northern coasts, is largely caused by Noctiluca, but by no means exclusively, since Medusae, Crustaceans, Annelids, and various Protozoa often take part in the phenomenon. Not unfrequently, however, the phosphor escence on the British coasts seems to be solely due to Noctiluca, which then occurs in millions in the littoral waters. FIG. XXIII. Ciliata. i. Spirostomum ainbiguum, Ehr.; one of the Hetero tricha; x 120. Observe on the right side the oral groove and special hetero- trichous band of long cilia, a, moniliform nucleus ; b, contractile vacuole. 2. Stentor polymorphus, Miiller ; oiie of the Heterotricha ; x 50 ; group of individuals with the area fringed by the heterotriclious cilia expanded trumpet-wise. 3. Tintinnns layenvla, C. and L.; one of the Hetero tricha; x 300. 4. Strombidium Claparedii, S. K.; one of the 1 eritricha; x 200. 5. Empty shell of Codonella campanella, Haeck.; one of the Heterotricha ; x 180. 0, 7. ToryuateOa typica, Laukester. p, the supra- oral lobe seen through the membranous collar. 8, 9. View of the base and of the side of Trichodina pediculus, Ehr.; one of the Peritricha; x 300. a, nucleus ; c, corneous collar ; d, mouth. 10. Spirochona gemmipara, Stein ; one of the Peritricha ; x 350. a, nucleus ; g, bud 11. VortieeUa citrina, Ehr.; x 150 (Peritricha). At d multiple fission of an individual cell to form "microgonidia." 12. VortieeUa microstmna Ehr. (Peritricha) ; x 300. At e eight "microgonidia" formed by fission of a single normal individual. 13. Same species, binary fission, a, elongated nucleus. 14. VortieeUa nebulifera, Ehr. ; free-swimming zooid resulting from fission in the act of detaching itself and swimming away, possessing a posterior circlet of cilia, e, ciliated disk ; /, Pharynx. 15. VortieeUa microstoma, Ehr. ; normal zooid with two microgonidia (or microzooids) c,d, in the act of conjugation, a, nucleus ; b, contractile vacuole ; e, ciliated disk ; /, pharynx. 16, VortieeUa microstoma, Ehr., with stalk contracted and body enclosed in a cyst, o, nucleus. 17. VortieeUa nebulifera, Ehr. a, nucleus ; b, contractile vacuole ; c, muscular region of the body continuous with the muscle of the stalk; d, pharynx (the basal continuation of the oral vestibule which receives at a higher point the foacal excreta and the ejected liquid from the contractile vacuole). 18. Carchesium upectabile, Ehr. ; retractile colony; x 50. 19 Trichocysts of Epistylis Jlavicanx, Ehr., as figured by Greeff. 20. Opercularia stenostoma, Stein ; x 200 ; a small colony. Observe the ciliation ot the oral vestibule and the upstanding ciliate disk (opercular-like). 21, 22. I yxicola affinis, S. K.; one of the stalked loricate Peritricha, in expanded and retracted states, x, the true oper- culum. 23, 24. Qyrocoris oxyura, Stein ; one of the free-swimming Peritricha, with spiral equatorial cilia-band ; x 250. b, contractile vacuole. 25, 26. Thuricola valvata, Str. Wright ; one of the sessile tubicolous Peritricha. Two individuals are as a result of fission tempo rarily occupying one tube ; 11, the valve attached to the tube, like the door of the trap-door spider s nest and the valve of the Gasteropod Clausilium. CLASS V. CILIATA, Ehrenberg (Infusoria sensu stricto). Characters. Corticata of relatively large size, provided with either a single band of cilia surrounding the anteriorly placed oral aperture or with cilia disposed more numerously over the whole surface of the body. The cilia are distinguished from the flagella of Flagellata by their smaller size and simple movements ot alternate flexion and erection ; they serve always at some period of growth as locomotor organs, and also very usually as organs for the introduction of food particles into the mouth. Besides one larger oblong nucleus a second (the paranucleus) is invariably (?) present (Fig. XXV. 2), or the nucleus may be dispersed in small fragments. Conjugation of equal-sized individuals, not resulting in permanent fusion, is frequent. The conjugated animals separate and their nuclei and paranuclei undergo peculiar changes ; but no formation of spores, either at this or other periods, has been de cisively observed (Fig. XXV. 8 to 15). Multiplication by transverse fission is invariably observed in full-grown individuals (Fig. XXV. 16), and conjugation appears to take place merely as an interlude in the fissiparous process ; consequently young or small Ciliata are (with few exceptions) unknown. Possibly spore-formation may hereafter be found to occur at rare intervals more generally than is at present supposed (Fig. XXIV. 15, 18). A production of micro- gouidia by rapid fission occurs in some Peritricha (Fig. XXIII. 11, 12, 14, 15), the liberated microgonidia conjugating with the normal individuals, which also can conjugate with one another. The Ciliata, with rare exceptions (parasites), possess one or more contractile vacuoles (Fig. XXV. 3). They always possess a delicate cuticle and a body-wall which, although constant, in form is elastic. They may be naked and free-swimming, or they may form horny (Fig. XXIII. 21, 25) or siliceous cup-like shells or gelatinous envelopes, and may be stalked and form colonies like those of Choanoflagellata, sometimes with organic connexion of the con stituent units of the colony by a branching muscular cord (Vorti- cellidre). Many are parasitic in higher animals, and of these some are mouthless. "All are holozoic in their nutrition, though some are said to combine with this saprophytic and holophytic nutrition. The Ciliata are divisible into four orders according to the distribution and character of their cilia. The lowest group (the Peritricha) may possibly be connected through some of its members, such as Strombidium (Fig. XXIII. 4), with the Flagellata through such a form as Lophomonas (Fig. XXI. 9). In the following synopsis, chiefly derived from Saville Kent s valuable treatise (71), the characters of the families and the names of genera are not given at length owing to the limitation of our space. ORDER 1. PERITRICHA, Stein (79). Characters. Ciliata with the cilia arranged in one anterior irclet or in two, an anterior and a posterior ; the general surface of the body is destitute of cilia. Sub-order 1. NATANTIA (animals never attached). Fam. 1. ToRQUATELLin/E. Genus. Torquatclla, Lankester, like Strombidium, but the cilia adherent so as to form a vibratile membranous collar (Fig. XXIII. 6, 7). Fam. 2. DICTYCCYSTID.E. Animals loricate.

Fam. 3. ACTIXOBOLID.E. llloricate, with retractile tentacula.