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principal siphon, surrounded by gonosiphons, and these again by tentacles.

Three families: (1) Discalidae, for Discalia and allied genera, deep-sea forms not well known; (2) Porpitidae for the familiar genus Porpita (fig. 69) and its allies; and (3) Velellidae, represented by the well-known genus Velella (figs. 70, 71), common in the Mediterranean and other seas.

II. Calycophorida (Calyconectae, Haeckel). Without pneumatophore, with one, two, rarely more nectocalyces.

Three families: (1) Monophyidae, with a single nectocalyx; examples Muggiaea, sometimes found in British seas, Sphaeronectes, &c.; (2) Diphyidae, with two nectocalyces; examples Diphyes (fig. 72), Praya, Abyla, &c.; and (3) Polyphyidae, with numerous nectocalyces; example Hippopodius, Stephanophyes and other genera.

EB1911 Hydromedusae - Physalia anatomy.jpg

From G. H. Fowler, modified after G. Cuvier and E. Haeckel, Lankester’s Treatise on Zoology.

Fig. 75.—A. Physalia, general view, diagrammatic; B, cormidium of Physalia; D, palpon; T, palpacle; G, siphon; GP, gonopalpon; M ♂, male gonophore; M ♀, female gonophore, ultimately set free.

III. Physophorida (Physonectae + Auronectae, Haeckel). With an apical pneumatophore, not divided into chambers, followed by a series of nectocalyces or bracts.

A great number of families and genera are referred to this group, amongst which may be mentioned specially—(1) Agalmidae, containing the genera Stephanomia, Agalma, Anthemodes, Halistemma, &c.; (2) Apolemidae, with the genus Apolemia and its allies; (3) Forskaliidae, with Forskalia and allied forms; (4) Physophoridae, for Physophora (fig. 73) and other genera, (5) Anthophysidae, for Anthophysa, Athorybia, &c.; and lastly the two families (6) Rhodalidae and (7) Stephalidae (fig. 74), constituting the group Auronectae of Haeckel. The Auronectae are peculiar deep-sea forms, little known except from Haeckel’s descriptions, in which the large pneumatophore has a peculiar duct, termed the aurophore, placed on its lower side in the midst of a circle of swimming-bells.

IV. Cystophorida (Cystonectae, Haeckel). With a very large pneumatophore not divided into chambers, but without nectocalyces or bracts. Two sections can be distinguished, the Rhizophysina, with long tubular coenosarc-bearing ordinate cormidia, and Physalina, with compact coenosarc-bearing scattered cormidia.

A type of the Rhizophysina is the genus Rhizophysa. The Physalina comprise the families Physalidae and Epibulidae, of which the types are Physalia (figs. 74, 75) and Epibulia, respectively. Physalia, known commonly as the Portuguese man-of-war, is remarkable for its great size, its brilliant colours, and its terrible stinging powers.

Bibliography.—In addition to the works cited below, see the general works cited in the article Hydrozoa, in some of which very full bibliographies will be found.

1. G. J. Allman, “A Monograph of the Gymnoblastic or Tubularian Hydroids,” Ray Society (1871-1872); 2. A. Brauer, “Über die Entwickelung von Hydra,” Zeitschr. f. wiss. Zool. lii. (1891), pp. 169-216, pls. ix.-xii.; 3. “Über die Entstehung der Geschlechtsprodukte und die Entwickelung von Tubularia mesembryanthemum Allm.,” t.c. pp. 551-579, pls. xxxiii.-xxxv.; 4. W. K. Brooks, “The Life-History of the Hydromedusae: a discussion of the Origin of the Medusae, and of the significance of Metagenesis,” Mem. Boston Soc. Nat. Hist. iii. (1886), pp. 259-430, pis. xxxvii.-xliv.; 5. “The Sensory Clubs of Cordyli of Laodice,” Journ. Morphology, x. (1895), pp. 287-304, pl. xvii.; 6. E. T. Browne, “On British Hydroids and Medusae,” Proc. Zool. Soc. (1896), pp. 459-500, pls. xvi., xvii., (1897), pp. 816-835, pls. xlviii. xlix. 12 text-figs.; 7. “Biscayan Medusae,” Trans. Linn. Soc. x. (1906), pp. 163-187, pl. xiii.; 8. “Medusae” in Herdman, Rep. Pearl Oyster Fisheries, Gulf of Manaar, iv. (1905), pp. 131-166, 4 pls.; 9. “Hydromedusae with a Revision of the Williadae and Petasidae,” Fauna and Geogr. Maldive and Laccadive Archipelagos, ii. (1904), pp. 722-749, pls. liv.-lvii.; 10. “On the Freshwater Medusa liberated by Microhydra ryderi, Potts, and a Comparison with Limnocodium,” Quart. Journ. Micr. Sci. I (1906), pp. 635, 645, pl. xxxvii.; 10a. “On the Freshwater Medusa Limnocnida tanganicaeBudgett Memorial Volume (Cambridge, 1908, pp. 471-482, pl. xxviii.; 11. C. Claus, “Über die Struktur der Muskelzellen und über den Körperbau von Mnestra parasites Krohn,” Verhandl. zool. bot. Ges. Wien, xxv. (1876), pp. 9-12, pl. i.; 11a. C. Dawydov, “Hydroctena salenskii,” Mém. Acad. Imp. St. Pétersbourg (viii.) xiv. No. 9 (1903), 17 pp., 1 pl.; 12. A. Dendy, “On a Free-swimming Hydroid, Pelagohydra mirabilis,” n. gen. et sp., Quart. Journ. Micr. Sci. xlvi. (1903), pp. 1-24, pls. i. ii.; 13. H. Driesch, “Tektonische Studien an Hydroidpolypen,” (1) Jen. Zeitschr., xxiv. (1890), pp. 189-226, 12 figs.; (2) t.c. pp. 657-688, 6 figs.; (3) ibid. xxv. (1891), pp. 467-479, 3 figs.; 14. G. Duplessis, “On Campanularia volubilis,” Soc. Vaud. Bull. 13 (Lausanne, 1874-1875); 15. J. W. Fewkes, “On Mnestra,” Amer. Natural., xviii. (1884), pp. 197-198, 3 figs.; 16. S. Goto, “Dendrocoryne Inaba, Vertreterin einer neuen Familie der Hydromedusen,” Annot. Zool. Tokyo, i. (1897), pp. 93-104, pl. vi., figs. 106-113; 17. “The Craspe dote Medusa Olindias and some of its Natural Allies,” Mark Anniversary Volume (New York, 1903), pp. 1-22, 3 pls.; 18. H. Grenacher, “Über die Nesselkapseln von Hydra,” Zool. Anz. xviii. (1895), pp. 310-321, 7 figs.; 19. R. T. Günther, “On the Structure and Affinities of Mnestra parasites Krohn; with a revision of the Classification of the Cladonemidae,” Mitt. Stat. Neapel, xvi. (1903), pp. 35-62, pls. ii. iii.; 20. E. Haeckel, “Das System der Medusen,” Denkschr. med.-nat.-wiss. Ges. (Jena, 1879-1881); 21. “Deep Sea Medusae,” in Reports of the Challenger Expedition, Zool. iv. pt. 2 (London, 1882); 22. P. Hallez, “Bougainvillia fruticosa Allm. est le faciès d’eau agitée du Bougainvillia ramosa Van Ben.” C.-R. Acad. Sci. Paris, cxl. (1905), pp. 457-459; 23. O. & R. Hertwig, Der Organismus der Medusen (Jena, 1878), 70 pp., 3 pls.; 24. Das Nervensystem und die Sinnesorgane der Medusen (Leipzig, 1878), 186 pp., 10 pls.; 25. S. J. Hickson, “The Medusae of Millepora,” Proc. Roy. Soc. lxvi. (1899), pp. 6-10, 10 figs.; 26. T. Hincks, A History of British Hydroid Zoophytes (2 vols., London, 1868); 27. N. Iwanzov, “Über den Bau, die Wirkungsweise und die Entwickelung der Nesselkapseln von Coelenteraten,” Bull. Soc. Imp. Natural, Moscou (1896), pp. 323-355, 4 pls.; 28. C. F. Jickeli, “Der Bau der Hydroidpolypen,” (1) Morph. Jahrbuch, viii. (1883), pp. 373-416, pls. xvi.-xviii.; (2) t.c., pp. 580-680, pls. xxv.-xxviii.; 29. Albert Lang, “Über die Knospung bei Hydra und einigen Hydropolypen,” Zeitschr. f. wiss. Zool. liv. (1892), pp. 365-384, pl. xvii.; 30. Arnold Lang, “Gastroblasta Raffaelei. Eine durch eine Art unvollständiger Theilung entstehende Medusen-Kolonie,” Jena Zeitschr. xix. (1886), pp. 735-762, pls. xx., xxi.; 31. A. Linko, “Observations sur les méduses de la mer Blanche,” Trav. Soc. Imp. Nat. St Pétersbourg, xxix. (1899); 32. “Über den Bau der Augen bei den Hydromedusen,” Zapiski Imp. Akad. Nauk (Mém. Acad. Imp. Sci.) St Pétersbourg (8) x. 3 (1900), 23 pp., 2 pls.; 33. O. Maas, “Die craspedoten Medusen,” in Ergebn. Plankton Expedition, ii. (Kiel and Leipzig, 1893), 107 pp., 8 pls., 3 figs.; 34. “Die Medusen,” Mem. Mus. Comp. Zool. Harvard, xxiii. (1897), i.; 35. “On Hydroctena,” Zool. Centralbl. xi. (1904), pp. 240-243; 36. “Revision des méduses appartenant aux familles des Cunanthidae et des Aeginidae, et groupement nouveau des genres,” Bull. Mus. Monaco, v. (1904), 8 pp.; 37. “Revision der Cannotiden Haeckels,” SB. K. Bayer. Akad. xxxiv. (1904), pp. 421-445; 38. “Meduses,” Result. Camp.