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Show ] 396.] BRITISH HYDROIDS AND MEDUSA. 495 TEACHOMEDUS.E. Fam. GERYONIDJ;. LlRIANTHA APPENDICULATA (Forbes). Geryonia appendiculata Forbes (1848). Liriope appendiculata, Gegenbaur (1856) ; Agassiz (1862). Xanthea appendiculata, Haeckel (1864). Liriantha appendiculata, Haeckel (1879). This medusa was exceedingly abundant at Plymouth during the whole of September and the early part of October, 1893. As most of the specimens belonged to the early stages, I was able to trace its development. First Stage.-Umbrella sub-globose, from 1 to 2 m m . wide, and about as long. Velum very broad. On the margin of the umbrella there are four interradial tentacles, about half the length of the umbrella, and are usually carried in au upright position alongside the ex-umbrella. O n the inner side of these tentacles there are rows of nematocysts, which are directed outwards when the tentacle is alongside the umbrella. These tentacles remain throughout life. On the ex-umbrella, about one-third the distance from the margin, are situated four little, perradial, primary tentacles; each consists of a large cluster of nematocysts upon a short stalk. Within the bulb containing the nematocysts there is a fine whip-like tongue, which I have seen occasionally protruded and after moving rapidly about in every direction withdrawn again inside the bulb. These primary tentacles disappear later in life. The characteristic features of this stage are the primary perradial tentacles and the absence of a manubrium. Second Stage.-During this stage the manubrium commences to grow downwards, a continuation of the edge of tbe circular opening in the first stage. At the same time four perradial tentacles commence to grow from the margin of the umbrella. They differ considerably from the interradial tentacles, and are not carried in an upright position, but hang down or trail behind the umbrella when the medusa is in motion and can be extended to a considerable length. Each tentacle has numerous rings of nematocysts. The lateral primary tentacles on the umbrella are usually present, but one or two may be absent. Medusae belonging to this stage may be characterized by possessing four perradial tentacles on the margin of the umbrella, and a short manubrium, not reaching to the velum. Umbrella about 3 m m . in diameter and colourless. Third Stage.-This is really the commencement of the adult stage, as the gonads begin to develop upon the radial canals. The lateral tentacles disappear and small scars mark their former position upon the ex-umbrella. The manubrium extends slightly beyond the cavity of the umbrella. Umbrella about 4 m m . in diameter. 1 have divided the early stages into these three |
