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, "Cœlenterata (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.
1908.Annandale, "Observations on specimens of Hydra from Tibet, with notes on the distribution of the genus in Asia," Rec. Ind. Mus. ii, p. 311.
1910.Powell, "Lessons in Practical Biology for Indian Students" (Bombay).
1910.Lloyd, "An Introduction to Biology for Students in India" (London).

GLOSSARY OF TECHNICAL TERMS USED IN PART II.

Aboral (or basal disk)The disk by means of which a free polyp attaches itself to external objects.
CnidoblastThe living cell of the nematocyst or nettle-cell (q. v.).
CnidocilA minute bristle that projects on the surface in connection with a nettle-cell (q. v.).
ColumnThe upright or potentially upright part of a polyp (q. v.).
EctodermThe external cell-layer of the body-wall.
EndodermThe internal cell-layer of the body-wall.
Green (chlorophyll) corpusclesMinute green bodies contained in cells of polyps or other animals and representing a stage in the life-history of an alga (Chlorella).
MesoglœaThe intermediate, gelatinous layer of the body-wall.
Nettle-cell (nematocyst)A cell capsule full of liquid in which an eversible thread is coiled up.
Oral diskThe eminence that surrounds the mouth and is surrounded by tentacles.
PeristomeSee "oral disk."
PolypAn individual cœlenterate of simple structure that is fixed temporarily or permanently by one end of a more or less cylindrical body and possesses a mouth at the other end.
TentaclesFilamentous outgrowths (in Hydra hollow) of the body-wall round the mouth.

LIST OF THE INDIAN HYDRIDA.


Class HYDROZOA.

Order ELEUTHEROBLASTEA.