. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. MONOGRAPH ON THE HYDROIDA OF SOUTHERN AFRICA apical process^ stomach 17 subumbrella subumbrellar cavity marginal bulb- marginal tentacle interradius V£W\. ra dial canal circular canal. statocyst Fig. 10. Composite diagram of medusa to illustrate parts. a hypostome, or manubrium, which hangs from the centre, and opens into a stomach, or gastral cavity. From the latter lead radial canals, which com- municate with a circular canal round the margin. From the margin a velum, or horizontal ectodermal shelf
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. MONOGRAPH ON THE HYDROIDA OF SOUTHERN AFRICA apical process^ stomach 17 subumbrella subumbrellar cavity marginal bulb- marginal tentacle interradius V£W\. ra dial canal circular canal. statocyst Fig. 10. Composite diagram of medusa to illustrate parts. a hypostome, or manubrium, which hangs from the centre, and opens into a stomach, or gastral cavity. From the latter lead radial canals, which com- municate with a circular canal round the margin. From the margin a velum, or horizontal ectodermal shelf, projects inwards and demarcates a subumbrel- lar cavity within the bell. The margin also bears the marginal tentacles. At the top of the exumbrella a projecting cone may form an apical process and may contain an apical canal communicating with the stomach. The radial canals are usually four in number and impart a tetramerous symmetry to the whole. From their position the 'axes' or radii of the medusa are derived. The radial canals lie in the perradii; alternating with these are the interradii, and between the perradii and the interradii are the adradii. Occasionally the radial canals are branched or multiplied. The mouth may be simple and circular, Sarsia, or it may be drawn out into oral lips which may be folded or crenulated, Leuckartiara. It may also bear simple or branched oral tentacles. The latter may be borne on the edge of the mouth or may be set back, as in Bougainvillia, so as to arise just above it. The stomach and hypostome may be short, not reaching the edge of the bell, or may be long and extensile, hanging well below the bell. The jelly of the upper part of the bell may bulge down into the base of the stomach forming a PEDUNCLE. The MARGINAL TENTACLES may be SOLID or HOLLOW, FILIFORM, CAPITATE Or moniliform, these terms being used as in the hydranth (Fig. 3). They arise from a swelling of the margin, the marginal bulb, but in some Limnomedusae this.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
