_Hydra grisea_, Linné (Gmelin), Systema Naturæ (ed. 13), p. 3870 (1782). _Hydra pallens_, _id_., _ibid_. p. 3871. _Hydra vulgaris_, Ehrenberg, Abhandl. Akad. Wiss. Berlin, 1836, p. 134, taf. ii. _Hydra brunnea_, Templeton, London's Mag. Nat. Hist. ix, p. 417 (1836). _Hydra vulgaris_, Laurent, Rech. sur l'Hydre at l'Éponge d'eau douce (Voy. de la Bonite, Zoophytologie), p. 11, pl. i, pl. ii, figs. 2, 2'' (1844). _Hydra vulgaris_, Johnston, Hist. British Zoophytes (ed. 2), i, p. 122, pl. xxix, fig. 2 (1847). _Hydra vulgaris_, Hincks, Hist. British Hydroid Zoophytes, i, p. 314, fig. 41 (1868). _Hydra aurantiaca_, Kleinenberg, Hydra, p. 70, pl. i, fig. 1, pl. iii, fig. 10 (1872). _Hydra trembleyi_, Haacke, Zool. Anz. Leipzig, ii, p. 622 (1879). _Hydra grisea_, Jickeli, Morph. Jahrb. viii, p. 391, pl. xviii, fig. 2 (1883). _Hydra grisea_, Nussbaum, Arch. mikr. Anat. Bonn, xxix, p. 272, pl. xiii, pl. xiv, figs. 33, 37, 47 (1887). ? _Hydra hexactinella_, v. Lendenfeld, Zool. Jahrb. Jena, ii, p. 96, pl. vi, figs. 13, 14 (1887). ? _Hydra hexactinella_, _id_., Proc. Linn. Soc. N. S. Wales, x, p. 678, p. xlviii, figs. 1-4 (1887). _Hydra grisea_, Brauer, Zeit. wiss. Zool. Leipzig, lii, p. 169 (1891). _Hydra grisea_, Chun, in Brönn's Thier-Reichs, ii (2), pl. ii, figs. 2_b_, 2_c_, 5 (1892). _Hydra grisea_, Downing, Zool. Jahrb. (Anat.) Jena, xxi, p. 381 (1905). _Hydra orientalis_, Annandale, J. Asiat. Soc. Bengal, (new series) i, 1905, p. 72. _Hydra orientalis_, _id._, _ibid._ (new series) ii, 1906, p. 109. _Hydra orientalis_, _id._, Mem. Asiat. Soc. Bengal, i, p. 340 (1906). ? _Hydra orientalis_, Willey, Spol. Zeylan. Colombo, iv, p. 185 (1907). _Hydra grisea_, Weltner, Arch. Naturg. Berlin, lxxiii, i, p. 475 (1907). _Hydra vulgaris_, Brauer, Zool. Anz. xxxiii, p. 792, fig. 1 (1908). _Hydra orientalis_, Annandale, Rec. Ind. Mus. ii, p. 312 (1908). _Hydra grisea_, Frischholz, Braun's Zool. Annal. (Würzburg), iii, pp. 107, 134, &c., figs. 1 and 10-17 (1909). _Hydra grisea_, _id._, Biol. Centralbl. Berlin, xxix, p. 184 (1909). _Hydra vulgaris_, Brauer, Die Süsswasserfauna Deutschlands, xix, p. 192, figs. 336-338 (1909). _Hydra pentactinella_, Powell, Lessons in Practical Biology for Indian Students, p. 24 (Bombay, 1910). Phase _orientalis*_, Annandale. _Colour_ variable; in summer usually pale, in winter either deep orange, dull brown, or dark green. The cells do not contain spherical or oval coloured bodies. [Illustration: Fig. 29.--_Hydra vulgaris_, from Calcutta (phase _orientalis_). A=winter brood; B=summer brood, the same individual in an expanded and a contracted condition. B is more highly magnified than A.]