On the nature of these genital lamellae, see O. and R. Hertwig, J. Z. xiii. p. 599; Claus, Arb. Zool. Inst. Wien, i. 1878, p. 269 et seqq., and his Untersuchungen, p. 37. Their accounts differ.

2Haeckel believes that the Tesseroniae possess a Scyphostoma stage; Claus that they develope direct. The former is supported by Haacke, who has observed a young Charybdaea Rastonii in which a canal was prolonged aborally from the gastric cavity and closed at the apex of the ex-umbrella by a thin lamella. See Z. A. ix. 1886.

Most Acraspeda are pelagic; a few deep-sea forms are known. The Depastridae and Lucernaridae attach themselves by their peduncle to algae, etc. In some instances the Medusa frequents the surface of mud-banks and coral reefs, and often rests reversed, i. e. upon the convexity of the bell2. Cassiopeia polypoides from the coral banks of the Red Sea has an exumbrellar groove which acts as a sucker. The ectoderm cells of the groove secrete a plentiful mucus which cements the coral sand, and there is also an exumbrellar radial musculature. The Tesseroniae are for the most part small: the Cubomedusan Tamoya attains, however, a diameter of eight inches. Many Ephyroniae are large, e. g. Aurelia aurita four •inches, and the Rhizostome Pilema pulmo ( = Rhizostoma Cuvieri) two feet: but the Semostome family Cyaneidae contains the largest known Medusae. An old example of Cyanea arctica has been measured with a bell seven and-a-half feet across and tentacles a hundred and twenty feet long. Many Acraspeda are brilliantly coloured, and some of them, e. g.

Cotylorhiza, are inhabited by the symbiotic alga Zooxanthella (see pp. 242-4). Most of the fossil Medusae mentioned above, p. 746, belong to this sub-class.

Haeckel classifies the Acraspeda as follows in his System: I. Tesseroniae: rhopalia four or none; stomach surrounded by four wide per-radial gastric pouches separated by longer or shorter septa; genital organs lodged either in the subumbrellar wall or in the cavity of the gastric pouches. Bell of great depth, usually conical. There are three orders.

(1) Stauromedusae: no rhopalia; includes Tesseridae with Depastridae, and Lucernaridae. (2) Peromedusae with four interradial rhopalia. (3) Cubomedusae with four perradial rhopalia and lamellate genitalia, e.g. Charybdaea.

II. Ephyroniae: rhopalia eight, i. e. four per- and four inter-radial, rarely more numerous; stomach surrounded by 8, 16, or 32 gastric pouches or radial canals; genitalia attached to the subumbrellar wall of the central gastric cavity. Bell flat; for the most part disc-like. One order, Discomedusae, with the above-detailed characters; three sub-orders as follows: (1) Cannostomae: mouth simple, square; tentacles solid and usually short; the Ephyridae and Linergidae. (2) Semostomae: mouth a cross, the four oral angles prolonged into long arms; without a circumferential canal, Pelagiidae, e. g. Chrysaora, and Cyaneidae; with one, Flosculidae and Ulmaridae; the last-named includes Aurelia. (3) Rhizostomae: mouth obliterated; four oral arms divided into eight; edges of their grooves united, leaving funnel-shaped apertures; four sub-genital cavities separate, Toreumidae, e.g. Cassiopeia, and Pilemidae, e.g. Pilema, or united to form a syndemnium, Versuridae, e.g. Cotylorhiza, and Crambessidae.

1 It is possible that the planula of Chrysaora may multiply by fission or gemmation: cf. Claus, Untersuchungen, p. 5, and Dk. Wien. Akad. xxxviii. p. 7. Haeckel has described such phenomena together with remarkable forms of Scyphostoma, and even a direct development similar to that of Pelagia in his 'Metagenesis and Hypogenesis von Aurelia aurita,' Jena, 1881. Claus in his Untersuchungen criticises (passim) Haeckel's statements unfavourably. Note his corrigendum, p. 90.

2 The young Cotylorhiza may attach itself in the same fashion, according to Keller.

Claus, in the Arb. Zool. Inst. Wien, vii. p. 109, divides the sub-class as follows: I.Tetrameralia: with four radial sectors.

Orders (I) Calycozoa=Depastridae and Lucernaridae: (2) Marsupialida, including Charybdaea and its allies.

II. Octomeralia: with eight sectors. Order Discophora with two sub-orders: - (1) Catammnata, with persistent septal unions1 including Haeckel's Peromedusae and Cannostomae: (2) Acatammnia, with no septal unions, but with a gastral lamella and the oral angles prolonged into arms, subdivided into (a) Mono-stomeae (==Semostomae) and (b) Rhizostomeae.

For the families he refers to his Untersuchungen, pp. 24 and 60.

Haeckel, System der Medusen, Dk. med. wiss. Gesellschaft, Jena, i. pt. 2 and Atlas, 1879; Id. Deep-sea Medusae, Challenger Reports, iv. 1882, p. 48; Claus, Untersuchungen iiber die Organ. und Entwick. der Medusen, Leipzig, 1883; Id. Dk. Wien. Akad. xxxviii. 1878; cf. for points of Anatomy, O. and R. Hertwig, Organismus der Medusen, Jena, 1878, and Nervensystem und Sinnesorgane der Medusen, Leipzig, 1878; L. Agassiz, Contributions to the Nat. Hist, of U. S., iv. pt. 3, Boston, 1862.

Lucernariae and their allies, Clark, Smithsonian Contributions to Knowledge, 1878; Craterolophus Tethys, Kling, M. J. v. 1879. Charybdaea marsupialis, Claus, Arb. Zool. Inst. Wien, i. 1878. Nausithoe, Claus, Untersuchungen, etc, (supra), p. 24; Aurelia, (= Medusa auritd), Ehrenberg, Akalephen des Rothen Meeres, Phys. Abhandl. Akad. Berlin, 1835; ditto, Chrysaora, etc. (and development), Claus, Dk. Akad. Wien, xxxviii; Aurelia, Cyanea, Pelagia, Stomolophus, Polyclonia, L. Agassiz, Contributions, etc. (supra); Cyanea Annaskala, von Lendenfeld, Z. W. Z. xxxvii. 1882; C. arctica, Wagner, Wirbellosen des Weissen Meeres, Leipzig, 1885, p. 83. Cassiopeia polypoides, Keller, Z. W. Z. xxxviii. 1883, p. 632; Rhizostoma Cuvieri, = Pilema pulmo, Brandt, Mem. Imp. Acad. St. Petersburg (7), xvi. 1871 metamorphosis of ditto and of Cotylorhiza, Claus, Untersuchungen, etc. (supra), p. 43, and Arb. Zool. Inst. Wien, v. 1884; Pseudorhiza aurosa, von Lendenfeld, Z. A. v. 1882, p. 380; Ps. Haeckelii, Haacke, Biol. Centralblatt, iv. 1884-85, p. 291; Crambessa Tagi, Grenacher and Noll, Abhandl. Senckenberg Ges. x. 1876, and Greeff, Z. A. iv. 1881.

Oral arms of Rhizostomae, Hamann, J. Z. xv. 1882.

Monstrous forms of Aurelia, Romanes, J. L. S. xii. 1876, p. 527; xiii. 1878, p. 191, with two plates; Ehrenberg, op. cit. supra, p. 199, and Pl. II.

Development of genitalia in Lucernaria, Craterolophus, Charybdaea, Aurelia, Discomedusa, Chrysaora, Claus, Untersuchungen, etc. (supra), p. 39 et seqq.; cf. p. 88; cf. also O. and R. Hertwig, J. Z. xiii. 1879, p. 599 et seqq. Formation of sperm in Cassiopeia borbonica (= Cotylorhiza tuberculata), Merejkowski, A. Z. Expt. x. 1882.

1By septal unions (Septalknoten) Claus appears to mean from p. 27 of the Untersuchungen, four interradial spots to the outer or abaxial side of the gastral filaments where the exumbrellar and, subumbrellar layers of endoderm have fused: cf. note 2, p. 784, and note, p. 786, ante.

Development of Lucernatia, Korotneff, Z. A. vii. 1884. Young stage of a Charybdaea, Haacke, Z. A. ix. 1886. Egg and Scyphostoma of Nausithoe mar-ginata, Metschnikoff, Embryol. Studien an Medusen, Wien, 1886, pp. 28 and 86; ditto and Strobila of Aurelia and Chrysaora, Claus, Untersuchungen, etc, and Dk. Akad. Wien, xxxviii. (supra), with lit. cited; cf. on Aurelia and Cotylorhiza, Gotte, Abhandl. zur Entwickelungsgeschichte der Thiere, pt. iv. 1886; and pp. 747-8, ante. Cf. Haeckel, System (supra), p. 474; also von Lendenfeld, Proc. Lin. Soc. N. S. Wales, ix. 1885, for ontogeny of Cyanea Annaskala, p. 275, of Pseudorhiza aurosa, p. 293, and Stylorhiza punctata, p. 297. Ontogeny of Pelagia, Krohn, Archiv f. Anat. und Physiol. 1855, p. 491; Kowalewsky, in Hoffmann and Schwalbe's Jahresbericht, ii. 1873, p. 280; and L. Agassiz, Contributions (supra), p. 128. Scyphostoma of Rhizo-stoma (=Rilema), Claus, Z. A. iv. 1881, p. 79.

Medusa in reversed position, Guppy, Nature, xxvii. 1882-83, P- 31 (with ref.); Keller on Cassiopeia (supra); Id. on Cotylorhiza, Recueil Zool. Suisse, i. 1884, p. 405.

Local colour varieties of Scyphomedusae, von Lendenfeld, A. N. H. (5), xiv. 1884. Colouring matter of Jellyfish, McKendrick, Journal of Anat. and Physiol, xv. 1881; of Rhizostoma (= Cyanein), Blanchard, Z. A. vi. 1883; Krukenberg, ibid. Zooxanthellae in Cotylorhiza, Keller, Recueil Zool. Suisse, i. 1884, p. 413.

Locomotor system of Medusae, Romanes, Ph. Tr. 166, 1876; 167, 1877; 171, 1880; Eimer, Die Medusen physiologisch und morphologisch auf ihr Nervensystem untersucht, Tubingen, 1878. Cf. Wagner, Wirbellosen des Weissen Meeres, 1885, pp. 81-2.