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Show 1896.] BRITISH HYDROIDS AND MEDUSA. 477 Claparede discovered it off Arran Island, in the Firth of during September 1859. I do not think that Claparede's medusa is a distinct species, but a sta<*e in the development of Lizzia blondina. DISTRIBUTION. Heligoland, Haeckel. Scotland-Shetland Islands, Forbes. Bell Bock (East coast), M'Intosh. Arran Island, Claparede. England-Plymouth, E. T. B. Fowey, Peach. Falmouth, Val-lentin. Isle of Man, Browne. Ireland-Valencia Island, E. T. B. MARGELLIUM OCTOPUNCTATUM (Sars). Cytceis octopunctata, Sars (1836) (1846). Lizzia octopunctata, Forbes (1848); Peach (1849); Agassiz (1862); Bohm (1878); Clubb (1886); M'Intosh (1890) ; Vallentin (1893). Lizzia grata, Agassiz (1865). Rathkea octopunctata, Haeckel (1879) ; Giard (1888); Garstang (1894): Allen (1895;. Margellium octopunctatum, Haeckel (1879); Browne (1895). Margellium gratum, Haeckel (1879). The medusa first reproduces itself by means of buds upon the stomach, and when it reaches the adult condition either ova or spermatozoa appear upon the wall of the stomach ; the sexes being separate. What becomes of the ova after leaving the medusa is at present unknown. The ovum may give rise to a hydroid form or develop directly into a medusa. The young medusae on leaving their parent have not always the same number of tentacles. There are usually three tentacles in each of the four perradial groups, but occasionally only two ; the interradial groups may have either two or three tentacles, rarely only one. As the medusa grows the perradial tentacles increase to five in each group, and the interradial tentacles to three in each group., The change in the number of tentacles has led to some of the early stages being described as distinct species. Sars first described the medusa (Cytceis octopunctata) from specimens with three tentacles in all the groups (-Rathkea of Haeckel). Forbes described specimens (Lizzia octopunctata) having either two or three tentacles in the perradial groups, and three tentacles in the interradial groups. Porbes regarded these specimens as belonging to the same species as those described by Sars. Haeckel, however, has separated these specimens into two genera : those with two tentacles in the perradial groups are placed in the genus Margellium; the others in the genus Rathkea. I have already shown, in the Eeport on the Medusae of the Isle of Man, that Forbes was right in regarding his specimens as identical with the medusae described by Sars as Cgtceis octopunctata. Garstang has also shown that Haeckel was wrong in separating these medusae into two distinct genera. |