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Show 830 MB. E. T. BROWNE ON BRITISH MEDUSJE. [Nov. 16, 55 mm. in diameter, keeps pace with the growth of the umbrella and becomes longer and more funnel-shaped. The mouth, as in all these specimens, has a considerable number of folds and is capable of considerable expansion (35 m m . in diameter when expanded). There are 43 tentacles of various sizes, and between every two tentacles usually one large and two small marginal bulbs, and between the latter several marginal vesicles. Tbe radial canals (153 in number) nearly all enter the ring-canal. The genital bands are very conspicuous. The velum is about 4 m m . broad. No. 6. Umbrella ]60 m m . in diameter. This is the largest specimen of the series, and to judge from the immature condition of the ova the medusa bas not yet reached its full development and probably grows to a larger size. The diameter of the stomach is 53 mm., and the mouth has a very large number of folds. There are 56 tentacles, and between every pair of tentacles usually one large and two small bulbs, which may develop tentacles later on. The radial canals are only 88 in number and nearly all join the ring-canal, and nearly all have generative cells in different stages of development. The following is a general description of the different organs of the specimens above described :- The Stomach and Mouth. The stomach is remarkable on account of its size; the upper part, as already stated, is circular and convex in shape; the convexity is more marked in the larger specimens. In shape, the stomach is like a short, broad funnel with the side marked by longitudinal lines, like frosted glass, which alternate with the openings of the radial canals. The lines extend from the base of the stomach up to the edge of the mouth. The closing of the mouth is effected by the wall of the stomach becoming spirally twisted. When the mouth is closed the stomach becomes more elongated and the twisted portion forms a kind of oesophagus (" Schlundrohr" of Haeckel), just as in Polycanna fungina, Haeckel (Taf. xiv. fig. 4). The mouth does not always hang in the centre of the umbrella-cavity, but at times moves very slowly round and round the margin of the stomach. The edge of the mouth, in the smallest specimen, has simple folds, which become more complex in the larger specimens. The Radial Canals and Generative Organs. Allman gives in his Monograph (p. 79) an excellent diagram showing the development of the radial canals of an HZquorea (probably AVquorea forskalea, Forbes). The specimens taken at Valencia show that the radial canals do not develop in any definite order. In the smallest specimen about one-third join the ring-canal, and tbe remainder show various stages of growth-some of them are only just leaving the stomach. The number of canals appears to be very variable, as the largest specimen has only 88 canals, and |
