The affinities of the Acinetaria are very obscure. The fact that the bud is ciliated does not necessarily attach them to Infusoria, and Stein's view that they are embryonic forms of different Infusorians has been laid to rest long ago. It is probable, however, that they are descended from ciliated ancestors, and a remarkable Infusorian, Actinobolus radians, is known which is provided with retractile tentacles. The latter appear to be used for the softening of the cellulose membrane of the cells of Cladophora; see Geza Entz, Z. W. Z. xxxviii. pp. 169, 171-2. He points out that the ends of the tentacles in Acinetaria kill and assist in breaking up the prey. See his remarks on affinities, pp. 173 - 5.

The Acinetaria are classified as follows by Saville Kent: I. Suctoria. Suctorial tentacles, with or without adhesive tentacles (= retinacula).

(a) Non-colonial. Rhynchaetidae, one or two tentacles only: Rhynchaeta, motile and naked; Urnula, sessile and loricate. Acinetidae, tentacles simple and numerous; (1) naked, with tentacles all suctorial, the free-swimming Sphaerophrya, the sessile and irregularly shaped Trichophrya, the pedicellate Podophrya, or with tentacles suctorial and adhesive, Hemiophrya; (2) loricate with suctorial tentacles, the sessile Solenophrya, the pedicellate Acineta, with tentacles suctorial and adhesive, Podocyathus. Dendrocomeiidae, sessile, with 4-6 branched arms, Den-drocometes paradoxus.

(b) Colonial. Dendrosomidae, sessile, with branched stems and stolon, Den-drosoma radians.

II. Actinaria (s. Non-Suctoria, E. Ray Lankester). Only retinacula. Ephelotidae, tentacles simple, ray-like; animals pedicellate; the naked Ephelota, and loricate Actinocyathus. Ophryodendridae, tentacles represented by one or more retractile proboscidiform organs; the organ simple, Acinetopsis, or with terminal cirri, Ophryodendron; but see note 1, p. 827, ante.

Plate proposes (Z. W. Z. xliii. p. 198) to divide the class into (1) Radiformiae, with isolated tentacles, and (2) Fascicularia, with tentacles borne upon arms or proboscides. The second subdivision includes Dendrocometes and Ophryodendron.

Saville Kent, Tentaculifera, Manual of the Infusoria, ii. 1880-1, pp. 801-56; Maupas, 'Contributions,' etc. A. Z. Expt. ix. 1881; Fraipont, 'Recherches,' etc. Bull. Acad. Roy. Belg. xliv. 1877; xlv. 1878; R. Hertwig, 'Beitrage,' etc. M. J. i. 1876, pp. 50-80.

Rhynchaeta, Zenker, A. M. A. ii. 1866, p. 345. Acineta gelatinosa, Buck, Ber. Senck. Ges. 1884; Acinetae and Ophryodendron variabile, Gruber, Nova Acta, xlvi. 1884, pp. 526-33; Dendrocometes, Plate, Z. W. Z: xiii. 1886, pp. 175-200. Many Acinetaria are described in papers relating to Infusoria: such papers are denoted by an asterisk on p. 839, infra.

Changeability of form: in Acineta Livadina, Mereschkowski, A. N. H. (5), vii. 1881, p. 214; in Ophryodendron variabile, Gruber, op. cit. supra.

Assumption of a motile phase. Podophrya libera = P. fixa var. Algirensis, Maupas, A. Z. Expt. v. 1876; P. fixa, R. Hertwig, op. cit. p. 78, note; Acineta mystacina, Biitschli, M. J. x. 1877, p. 307; Dendrocometes, Plate, op. cit. supra.

Paranuclei, Maupas, A. Z. Expt. ix. 1881, p. 360. Gas bubble in a Sphae-rophrya, Engelmann, Z. A. i. 1878, p. 152.

Fission: Urnula, Claparede and Lachmann, Etudes sur les Infusoires, etc. ii.

1860-1, p. 208; Podophrya libera=fixa, Maupas, A. Z. Expt. v. 1876, p. 409; P. fixa, Cienkowski, Bull Imp. Acad. St. Petersburg, xiii. 1855, columns 299-300;

Carter, A. N. H. (3), xv. 1865, p. 287; P. mollis, note 2, p. 827, ante; Acineta mystacina, Biitschli, J. Z. x. 1877, p. 307; cf. Gruber, Z. W. Z. xxxvi. 1882, p. 118.

Gemmation. (1) External; Hemiophrya-= Podophrya gemmipara, R. Hertwig, M. J. i. 1876; H. = P. Benedeni, Fraipont, op. cit. supra, xlv. p. 278; Ophryoden-dron Belgicum, Id. op. cit. xliv. p. 784. (2) Internal; Podophrya quadripartita, Biitschli, J. Z. x. 1877; Trichophrya, Id. ibid. p. 308; Dendrocometes, Plate, op. cit. supra. Cf. note 1, p. 828, ante. Embryoes are described in the general works, supra.

Conjugation-. Claparede and Lachmann, op. cit. supra, ii. pp. 122, 123, 136, 228-9; Fraipont, op. cit. xlv. p. 502; cf. note 2, p. 827, ante; in Dendrocometes, Plate, op. cit. supra; A. Schneider, Tablettes Zoologiques, Poitiers, i. 1886, p. 82.