_Hydra_ has been examined by thousands of students in biological laboratories all over the civilized world, and the literature upon it is hardly surpassed in magnitude by that on any other genus but _Homo_. The following is a list of a few of the more important general memoirs and of the papers that refer directly to Asiatic material. A systematic bibliography is given by Bedot in his "Matériaux pour servir a l'Histoire des Hydroïdes," Rev. Suisse Zool. xviii, fasc. 2 (1910). (a) _General._ 1743. BAKER, "An attempt towards a natural history of the Polyp"* (London). 1744. TREMBLEY, "Mémoires pour servir à l'histoire d'un genre de polypes d'eau douce"* (Paris). 1755. RÖSEL VON ROSENHOF, "Insecten-Belustigung: iii, Hist. Polyporum." 1766. PALLAS, "Elenchus Zoophytorum." 1844. LAURENT, "Rech. sur l'Hydre et l'Eponge d'eau douce" ("Voy. de la Bonite, Zoophytologie"). 1847. JOHNSTON, "A History of the British Zoophytes" (2nd edition). 1868. HINCKS, "History of British Hydroid Zoophytes." 1872. KLEINENBERG, "Hydra. Eine Anatomisch Entwicklungsgeschichtliche Untersuchung." 1882. JICKELI, "Der Bau der Hydroidpolypen," Morph. Jahrb. viii, p. 373. 1887. NUSSBAUM, "Ueber die Theilbarkeit der lebendigen Materie. II. Mittheilung. Beiträge zur Naturgeschichte des Genus Hydra," Arch. mikr. Anat. Bonn, xxix, p. 265. 1891. BRAUER, "Über die Entwicklung von Hydra," Zeitschr. wiss. Zool. Leipzig, lii, p. 169. 1892. CHUN, "Coelenterata (Hohlthiere)," in Bronn's Thier-Reichs II (2). 1905. DOWNING, "The spermatogenesis of Hydra," Zool. Jahrb. (Anat.) xxi, p. 379. 1908. BRAUER, "Die Benennung und Unterscheidung der Hydra-Arten," Zool. Ann. xxxiii, p. 790. 1909. FRISCHHOLZ, "Biologie und Systematik im Genus Hydra," Braun's Annal. Zool. (Würzburg) iii, p. 105. 1910. BERNINGER, "Über Einwirkung des Hungers auf Hydra," Zool. Anz. xxxvi, p. 271. (b) _Asiatic References._ 1894. RICHARD, "Sur quelques Animaux inférieurs des eaux douces du Tonkin (Protozoaires, Rotifères, Entomostracés)," Mém. Soc. zool. France, vii, p. 237. 1904. VON DADAY, "Mikroskopische Süsswasserthiere aus Turkestan," Zool. Jahrb. (Syst.) xix, p. 469. 1906. ANNANDALE, "Notes on the Freshwater Fauna of India. No. IV. _Hydra orientalis_ and its bionomical relations with other Invertebrates," J. Asiat. Soc. Bengal (new series), ii, p. 109. 1906. ANNANDALE, "The Common _Hydra_ of Bengal: its Systematic Position and Life History," Mem. As. Soc. Bengal, i, p. 339. 1907. ANNANDALE, "Notes on the Freshwater Fauna of India. No. X. _Hydra orientalis_ during the Rains," J. Asiat. Soc. Bengal (new series), iii, p. 27. 1907. ANNANDALE, "Notes on the Freshwater Fauna of India. No. XI. Preliminary Note on the occurrence of a Medusa (_Irene ceylonensis_, Browne) in a brackish pool in the Ganges Delta and on the Hydroid Stage of the species," J. Asiat. Soc. Bengal (new series), iii, p. 79. 1907. WILLEY, "Freshwater Sponge and Hydra in Ceylon," Spolia Zeylan. Colombo, iv, p. 184.