I. Trachymedusae, Haeckel, System der Medusen, Jena, 1879, pp. 234-359; Id. Deep-sea Medusae, Challenger Reports, iv. 1882, pp. 9-48; anatomy of various species, see in O. and R. Hertwig, Das Nervensystem und die Sinnesorgane der Medusen, Leipzig, 1878; Iid. Organismus der Medusen, Jena, 1878; Nervous system, etc, of Carmarina, Eimer, Die Medusen physiologisch, etc, auf ihr Nervensystem untersucht, Tubingen, 1878. Cf. on Liriope eurybia and Carmarina hastata, Haeckel, J. Z. ii. 1866; critical notes on genera, etc., Metschnikoff, Medusologische Mittheilungen, Arb. Zool. Inst. Wien, vi. 1886, p. 244 (pp. 8 et seqq. of paper).

1For another classification cf. von Lendenfeld, Z. A. vii. 1884.

2Beneath the central gastrozooid of the Discoideae lies a mass of tissue often spoken of as "liver.' Its structure has been worked out by Bedot, who terms it 'central organ.' It consists essentially of a mass of cnidoblasts and tubes. The latter are connected to the central zooid and the canals of the coenosarc, and form a dense layer beneath the pneumatophore, connected to a second but less dense superficial layer. The cells of the first layer contain coloured corpuscles in Velella,. granules and crystals of guanine in Porpita. The blastostyles and tentacles (dactylozooids) are connected to the canal system.

Freshwater Limnocodium, Allman, J. L. S. xv. 1881; E. Ray Lankester, Q. J. M. xx. 1880; developing forms of, Id. op. cit. xxi. 1881; hydroid form (?), A. G. Bourne, P. R. S. xxxviii. 1884. Medusa in Lake Tanganyika, Bohm and von Martens, SB. Ges. Natf. Freunde, Berlin, 1883, p. 197.

Eggs, segmentation, formation of germinal layers, Metschnikoff, Embryologische Studien an Medusen, Wien, 1886. Delamination in Liriope eurybia and Carmarina fungiformis, Id. Z. W. Z. xxxvi. 1882, p. 435.

Development of Cunoctantha octonaria, Brooks, Mem. Boston Soc. Nat. Hist, iii. 1886, p. 360, cf. Metschnikoff, Embryol. Studien, p. 123; C. Kollikeri, F. Muller, A. N. 27 (1), 1861; Sporogony of Cunina proboscidea, Metschnikoff, op. cit. p. 102; cf. also and on C. rhododactyla, Id. Z. W. Z. xxi v. p. 27; C. parasitica, Metschnikoff, Z. W. Z. xxxvi. 1882, p. 437, cf. Embryol. Studien, p. 122, Schulze, Mittheil. Vereins fur Steiermark, Graz. 1875 (Archiv fur Ges. Naturwissenschaften, 46, p. 494, or A. N. 41 (2), p. 404); for figures, Haeckel, J. Z. ii. Taf. ix. figs. 74-77, Fewkes, American Naturalist, xiv. 1880, p. 303, and F. Muller, A. N. 27, Taf. iv. fig. 30. Development of Polyxenia leucostyla (Solmoneta flavescens) and Aegi-nopsis (Solmundella) mediterranea, Metschnikoff, Embryol. Studien, and Z. W. Z. xxiv. 1874, p. 22.

Development of Aglaura, Metschnikoff, Embryol. Studien, supra, p. 93; Liriope mucronata, with re7narks on Geryonia proboscidalis (Carmarina hastatd), Id. ibid. p. 90; on last-named, also Z. W. Z. xxiv. p. 17; Geryonia (Carmarina) fungiformis, Fol, J. Z. vii. 1873; Liriope scutigera, Brooks, op. cit. supra, p. 373.

Metamorphosis of Liriope (Glossocodon) eurybia, Haeckel, J. Z. ii. 1866, p. 129; of Carmarina hastata, Id. ibid. p. 174; of Liriope Catharinensis, F. Muller, A. N. 25 (I), 1859.

II Hydroidea, see p. 249, ante.

Contributions to Nat. Hist.United States, L. Agassiz, iv. 1862, pp. 183 et seqq.; Wirbellosen des Weissen Meeres, Wagner, Leipzig, 1885, pp. 69-81; cf. Australian Hydromedusae, von Lendenfeld, Proc. Lin. Soc. New South Wales, ix; x. Antho-medusae andLeptomedusae, Haeckel, System der Medusen, Jena, 1879, pp. 3-233.

Hydroid forms: Hydra, pp. 328-9, ante; Microhydra, Ryder, American Naturalist, xix. 1885; Protohydra, Greeff, Z. W. Z. xx. 1870; Polypodium, p. 766, ante; Tiarella, Schulze, Z. W. Z. xxvii. 1876; Lar Sabellarum, Hincks, A. N. H. (4), x. 1872; Amphibrachium Euplectellae, Schulze, Trans. Royal. Soc. Edinburgh, xxix. 1880, p. 671; Monobrachium, Mereschkowsky, 'New genus,' etc, A. N. H. (4), xx. 1877; Sarsia radiata and its flexor muscles, von Lendenfeld, Z. A. vii. 1884; Cladocoryne, du Plessis, Mitth. Zool. Stat. Naples, ii. 1881; Myriothela, Allman, Ph. Tr. 165, 1875; Podocoryne, Grobben, SB. Akad. Wien, lxxi. Abth. 1. 1875, Hamann, J. Z. xv. 1882, p. 517; Oorhiza, Mereschkowsky, A. N. H. (5), i. 1878, p. 325, Wagner, op. cit. supra, p. 71; various genera, Jickeli, M. J. viii. 1883. For various hydroids reared from Medusan ova, see Metschnikoff, Embryol. Studien, infra; and for Turritopsis and Eutima, Brooks, infra.

Deep-water Hydroidea from Norway and Iceland, Hincks, A. N. H. (4), xiii. 1874; cf. Allman, Hydroidea of Porcupine, Tr. Z. S. viii. 1874; cf. Quelch, A. N. H. (5), xvi. 1885. Gigantic Monocaulus, Nature, xii. 1875, p. 555. Hydra and Cordylophora of Australia, von Lendenfeld, Spengel's Zool. Janrbucher, ii. 1886.

Sarcothecae, or machopolypes, von Lendenfeld, Z. W. Z. xxxviii. 1883, transl. A. N. H. (5), xii. 1883; Mereschkowsky, A. Z. Expt. x. 1882; cf. Metschnikoff, Q. J. M. xxiv. 1884, p. 91.

Medusa. Laodice (Cosmetira) salinarum, du Plessis, A. N. H. (5), iii. 1879; Mnestra parasites, Claus, Verhandl. z. b. Ges. Wien, xxv. 1876, Fewkes, American Naturalist, xviii. 1884, pp. 197-8; Orchistoma, Keller, 'Mittheilungen,' Recueil Zool. Suisse, i. 1884; Aequorea and its development, Claus, Untersuchungen uber die Organisation, etc., der Medusen, Leipzig, 1883, pp. 61 et seqq.; Octorchis with Campanopsis, Irene (=Tima), Phialidium, Id. Arb. Zool. Inst. Wien, iv. 1882; Gastroblasta timida, Keller, Z. W. Z. xxxviii. 1883, p. 622; history and development of Turritopsis and Eutima, W. K. Brooks, Mem. Boston Soc. Nat. Hist. iii. 1886, pp. 386-404; 'Notes,' etc., Id. Studies Biol. Lab. Johns Hopkins University, ii. 1883; 'Notes,' Fewkes, Amer. Naturalist, xviii. 1884; Eleutheria, Hartlaub, Z. A. ix. 1886.

Deep-sea forms, Haeckel, Challenger Reports, iv. 1882, pp. 1-9.

Fission in Medusae, Lang on Gastroblasta Rajfaelei, with lit. cited, J. Z. xix. 1886. Gemmation in ditto, see table in Bohm, J. Z. xii. 1879, p. 136; Brooks, American Naturalist, xiv. 1880, p. 670; Allman, Gymnoblastic Hydroids, Ray Soc. 1871, p. 82; Haeckel, 'System,' Pls. I and VI.

Egg and development, Metschnikoff, Embryologische Studien an Medusen, Wien, 1886; of Hydra, pp. 328-9, ante; of Tubularia, Ciamician, Z. W. Z. xxxii. 1879, Conn, Z. A. v. 1882; of Myriothela, Korotneff, Z. A. ii. 1879, cf. Allman, Ph. Tr. 1875; of Obelia, Mereschkowsky, Bull. Soc. Zool. France, viii. 1883; of Turritopsis and Eutima, Brooks, Mem. Boston Soc. Nat. Hist. iii. 1886, (supra).

Migration of sexual cells in Obelia, Hartlaub, Z. W. Z. xli. 1885.

Origin of sexual cells; with many facts relating to the structure of the colony, the development of the egg, and Medusa, as well as to the structure of the sexual zooid, Weismann's Entstehung der Sexualzellen bei den Hydromedusen, Jena, 1883.

Hydrocorallina, Moseley, Challenger Reports, ii. 1881 (cf. Milleporidae, Ph. Tr. 167, 1877, and Stylasteridae, Ph. Tr. 169, 1878). Milleporidae, Quelch, Reef Corals, Challenger Reports, xvi. 1886, p. 190; ampullae in M. Murrayi, Id. p. 192 of Reef Corals, or in Nature, xxx. p. 539; generative capsules, Hickson, P. R. S. xl. 1886, p. 325. New Stylasteridae, Quelch, A. N. H. (5), xiii. 1884; xvi. 1885.

Graptolithidae s. Rhabdophora, Zittel, Handbuch der Palaeontologie, Abth. 1, Palaeozoologie, i. p. 290, or Nicholson's Manual of Palaeontology, 1879, i. p. 162; Lap worth, Geological Magazine, x. 1873; Id. on the geological distribution of ditto, A. N. H. (5), iii. and iv. 1879; v.and vi. 1880. Cf. Allman's critical remarks in the Gymnoblastic Hydroids, pp. 176-186, and p. 769, ante. Other fossil forms, Zittel, op. cit.; and cf. note 1, p. 756, ante.

III. Siphonophora. Oceanic Hydrozoa (with lit. p. 139), Huxley, Ray Society, 1858; Neue Beitrage, etc, Gegenbaur, Nova Acta, xxvii. 1860. Zur Kenntniss der Siphonophoren von Nizza, Leuckart, A. N. xx. (1), 1854; Zool. Untersuchungen, Id. Giessen, 1853. Schwimmpolypen von Messina, Kolliker, Leipzig, 1853. Siphonophora of deep waters, Studer, Z. W. Z. xxxi. 1878. Cf. Fewkes, Bull. Mus. Harvard, ix. pp. 246, 302.

Halistemma tergestinum, Claus, Arb. Zool. Inst. Wien, I, 1878; Agalmopsis utricularia, Id. op. cit. ii. 1879; Porpitidae and Velellidae, Agassiz, Mem. Harvard Mus. viii. 1881-84; Velella and Rataria, Bedot, Recueil Zool. Suisse, i. 1884; the same and Porpita, Id. op. cit. ii. 1885; Notes on Rhizophysa and Physalia, Chun, SB. Akad. Berlin, 1882, pp. 1168-70; Diphyes subtilis, Id. op. cit. 1886, p. 681; Diphyozooids, Id. ibid. p. 686; Cyclical evolution and Monophyidae, see p. 774, ante.

Histology in general, Korotneff, Mitth. Zool. Stat. Naples, v. 1884. Nervous system of Porpita, Conn and Beyer, Studies from Biol. Laboratory, Johns Hopkins Univ. iii. 1883; of Velella, Chun, Z. A. iv. 1881.

Origin of sexual cells. Weismann, Entstehung der Sexualzellen bei den Hydro-medusen, Jena, 1883, pp. 193-213; pp. 212, 265, 291.

Development. Entwickelungsgeschichte der Siphonophoren, Haeckel, Utrecht, 1869; Metschnikoff, Z. W. Z. xxiv. 1874; of Agalma, Fewkes, Bull. Mus. Harvard, xi. 1885.