The Infusoria are for the most part microscopic in size; some however are visible to the naked eye, e.g. Stentor polymorphtcs, which attains a length of 1/20 in.; so too the colonies of some Vorticellina, especially the arborescent colonies of Zoothamnium arbuscula; and Ophrydium versatile gives rise to gelatinous hollow masses 5 in. across when full grown. In-fusorians inhabit fresh, salt and brackish waters; some species, indeed, e. g. Chilodon cucullidus, Zoothamnium arbuscida are common to both fresh and salt. The faunae of different seas are not more dissimilar than are the faunae of different freshwaters, and many littoral or brackish-water forms are met with in salt lakes (Geza Entz). A few Infusorians are parasitic; some ectoparasitic, e. g. Ichthyophthirius on freshwater fish, others endo-parasitic in Vertebrata and Non-vertebrates alike, e. g. the Opalinidae. A Heterotrichan Balantidium coli is found in the large intestine of the human subject and in the rectum of swine. Dimorphism is restricted to certain colonial forms (p. 837) or products of fission or gemmation (p. 837 and note I).

The Infusoria are classified as follows: 1. Holotricha: free-swimming, more or less completely ciliate; cilia similar or slightly dissimilar, especially the adoral cilia; an extensile or undulatory membrane sometimes present; trichocysts not uncommon: Paramecium, Prorodon, Nassula, Coleps, Trachelitis, Ichthyophthirius, etc.; Opalinidae, e. g. Opalina, Anoplophrya, Benedenia.

2. Heterotricha: free or attached either at will, or rarely permanently; naked or tubicolous; cilia of small size covering the body, sometimes supplemented by nonvibratile setae; a set of adoral membranellae, disposed in a straight or curved line, in the latter case surrounding a peristomial area: Bursaria, Balantidium, Stentor; Tintinnodea, &C.1

1 Claparede and Lachmann, Etudes sur les Infusoires, etc. ii. p. 229 et seqq.; Stein, Organis-mus, etc. (infra), ii. pp. 10,113.

2 Gruber, Nova Acta, xlvi. pp. 520-1; cf. Geza Entz, Mitth. Zool. Stat. Naples, v. p. 418; Nachtrag, p. 439. Species of Amphileptus prey upon the colonial Vorticellidae, and encyst on the ends of the branches after a meal. Cf. Entz, op. cit. p. 420.

3. Peritricha: free or fixed; solitary or colonial; naked or tubicolous; with an adoral spiral of membranellae, or one or more ciliary girdles; otherwise destitute of cilia: see note 2 p. 832: Torquatella; Halteria; Didinium; Trichodina, etc.; Vorticellina, e. g. Vorticella, Epistylis, Carchesium, Spirochona; Vaginicolina, e. g. Vaginicola, Cothurnia; Ophrydina, e. g. Ophrydium.

4. Hypotricha: free, rarely tubicolous; with one surface, the ventral, flat, the other, the dorsal, more or less convex; ventral surface either entirely ciliate or with compound cilia disposed in special groups or lines; dorsal surface sometimes provided with immobile setae; adoral membranellae usually present; a complex peristome in two families (Oxytrichidae, Euplotidae): Chilodon, Loxodes, Dysteria, etc.; Stichotricha, Schizosiphon, Oxytricha, Stylonychia, etc.; Euplotes, etc.

Manual of the Infusoria, Saville Kent, ii. 1881-82 (with lit.); Organismus der Infusions-thiere, Stein, Leipzig, i. Hypotricha, 1859; ii. Heterotricha, 1867; Etudes sur les Infusoires, etc, Claparede and Lachmann, 2 vols., Geneva, 1858-61 (Me'm. Inst. Nat. Genevois, v. vi. vii).

* Protozoen des Hafens von Genua, Gruber, Nova Acta, 46, 1884, p. 509 et seqq.; *Infusorien des Golfes von Neapel, Ge'za Entz, Mitth. Zool. Stat. Naples, v. 1884; *Ein kleines Beitrag. etc, von Daday, ibid. vi. 1886; Contributions a l'e'tude morphol. et anat. des Infusoriens cilie's, Maupas, A. Z. Expt. (2), i. 1883: * Protozoaires des Vieux-Port de Marseille, Gourret, A. Z. Expt. (2), iv. 1886 j Neue Infusorien, Schizosiphon (= Stichotricha) soda/is, Maryna, etc, Gruber, Z. W. Z. xxxiii. 18782.

Holotricha. Coleps hirtus, Maupas, A. Z. Expt. (2), iii. 1885: C. fusus = Tiarina, Bergh, see Naples Zool. Jahresbericht, 1880, Protozoa, p. 170; Opalina, (various species), Zeller, Z. W. Z. xxix. 1877; Anoplophrya circulans, Schneider, Tablettes Zoologiques, Poictiers, i. 1886; Balbiani, Recueil Zool. Suisse, ii. 1885; Benedenia, Opalinopsis, Foettinger, Archives de Biologie, ii. 1881; Infusorian parasites of Termites, Leidy, Journal Acad. Nat. Sc. Philadelphia, (2), viii. 1881; Ichthyophthirius, Fouquet, A. Z. Expt. v. 1876.

Heterotricha. Bursaria truncatella, Brauer, J. Z. xix. 1885, Schubergh, M. J. xii. 1886; Folliculina (= Frejd) ampulla, Moebius, A. N. H. (5), xvi. 1885; Tin-tinnidium fluviatile, Codonella lacustris, Ge'za Entz, Mitth. Zool. Stat. Naples, vi. 1886 (with lit. on family, p. 214).

Peritricha. Actinobolus radians, Mesodinium acarus, and on limits of order, 'Beitrage,' etc, Ge'za Entz, Z. W. Z. xxxviii. 1883; Didinium, Balbiani, A. Z. Expt.

ii. 1873; Trichodina, Rosseter, Journal Roy. Micr. Soc. (2), vi. 1886; Epistylis, Ophrydium, etc, 'Beitrage,' Wrze'sniowski, Z. W. Z. xxix. 1877: Vorticella nebulifcra, Everts, Z. W. Z. xxiii. 1873; Vorticellidae, Greeff, A. N. 36, (1), 1871;

1By Saville Kent the Tintinnodea are divided between the Heterotricha and Peritricha; they appear to be entirely Heterotrichan. The Urceolarine Trichodinopsis he classifies similarly with the Heterotricha on account of its general ciliation; it is better to consider it as an aberrant Peritrichan. See references quoted, note 2, p. 832, ante.

2The asterisks mean that Acinetarians are included in the papers.

Dimorphic zooids of Z,oothcininium ophioidea, Kellicott, Journal R. Micr. Soc. (2), v. 1885, p. 78; Connection of Vorticellidae to other Infusoria, Biitschli, M. J. xi. 1885; Gerda, Phillips, J. L. S. xvii. 1883; Spirochona, Lagenophrys, Plate, Z. W. Z. xliii. 1886, pp. 200-15; Torquatella, E. Ray Lankester, Q. J. M. xiv. 1874.

Hypotricha, 'Beitrage,' etc, Oxytrichidae, Sterki, Z. W. Z. xxxi. 1878; cf. Wrze'sniowski on Kowalewski in Biol. Centralblatt. iii. 1883-4, p. 235.

General Anatomy, Maupas, A. Z. Expt. (2), i. 1883, pp. 570-661.

Envelope of Ophrydium, Halliburton, Q. J. M. xxv. 1885; Harker, Brit. Association Reports, 1885, p. 1074.

Adoral cilia = pectinellae, in Heterotricha and Hypotricha, compound nature of ventral cilia of latter, Moebius, Biol. Centralblatt. vi. 1886-7, P- 539 j cú van Rees, 'Zur Kenntniss der Bewimperung der Hypotrichen,' Amsterdam, 1881; action and insertion of cilia, Engelmann, Pfluger's Archiv fur Physiol, xxiii. 1880, pp. 507, 521, 530; Bristle of Vorticellidans=a membrane, Gruber, Z. W. Z. xxxiii. 1880, p. 460-1; Biitschli, Z. W. Z. xxviii. 1877, p. 67 on Fig. 21, Taf. vi; Ge'za Entz, Mitth. Zool. Stat. Naples, v. 1884, p. 417. Organs of attachment in Stentor, Gruber, Z. A. i. 1878.

Muscle fibrils, Brauer, J. Z. xix. 1886, pp. 500-11; Wrze'sniowski, Z. W. Z. xxix. 1877. pp. 287-95.

Glycogen, Maupas, C. R. ci. 1885, p. 1504; Barfurth, A. M. A. xxv. 1885, pp. 314-18. Birefringent corpuscles, Maupas, A. Z. Expt. (2), i. 1883, p. 616; ibid. iii. p. 352 and note. Stentorin, E. Ray Lankester, Q. J. M. xiii. 1873; chlorophyl, see p. 245, and note 3 p. 833, ante.

Nucleus and paranucleus, Jickeli, Z. A. vii. 1884; multinucleate forms, Gruber, Biol. Centralblatt. iv. 1884-5; Id. Z. W. Z. xl. 1884, pp. 140-48; Maupas, A. Z. Expt. (2), i. 1883, pp. 652-61; division of nuclei in Opalina, 'Zur Kenntniss,' etc, Pfitzner, M. J. xi. 1885.

Contractile vacuole, Wrze'sniowski, Z. W. Z. xxix. 1887, pp. 309-13; Fischer, Archives Slaves de Biologie, 1886; two in some Vorticellae, Stokes, Amer. Monthly Micr. Journal, vi. 1885; cf. Lembach, in Journal R. Micr. Soc. (2), 1882, p. 355.

Conjugation. Exchange and union of paranuclei - or their parts, Maupas, C. R. cii. 1886, p. 1569; ciii. 1886, p. 482; Gruber, A. N. H. (5), xviii. 1886, p. 164; exchange of parts of nuclei, Schneider, Tablettes Zoologiques, i. 1886, pp. 79-80; cf. Biitschli, Abhandl. Senck. Ges. x. 1876, pp. 262 et seqq; Engelmann, M. J. i. 1876; significance of process, Plate, Z. W. Z. xliii. 1886, pp. 215-28; p. 239.

Distribution of marine Infusoria, Ge'za Entz, Mitth. Zool. Stat. Naples, v. 1884, pp. 432-9; Marine Tintinnus in Swiss lakes, Imhof, Z. A. viii. 1885, p. 293.

Influence of light on growth, Fatigati, C. R. lxxxix. 1879, p. 959. Rate of multiplication, Maupas, C. R. civ. 1887, p. 1006; cf. Id. Leucophrys patula, ibid. ciii. 1886, p. 1270, and civ. 1887, p. 308.