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Show 470 MR. E. T. BROWNE O N [Mar. 17 The stomach is on a very short peduncle, and has six short prolongations or lobes from which the radial canals start. The mouth is variable in shape, being either round or with four to six lips. Six radial canals run from the lobes of the stomach direct to the ring-canal without giving off any branches. Six tentacles, equal in size, on the margin of the umbrella, one opposite the termination of each radial canal. The basal bulb of each tentacle is large and conspicuous, containing dark brown or blackish pigments. Midway between every two tentacles a small cluster of nematocysts is situated on the ex-umbrella just above the margin. This stage corresponds to the description given by Hincks of tbe medusa of Lar sabellarum. Second Stage. Twelve uniform tentacles.-The commencement of the second stage is indicated by the growth of six small bulbs on the margin of the umbrella, midway between the primary tentacles. From each of these bulbs a tentacle grows until it resembles in size the tentacles belonging to the first stage. A bulb on its first appearance is of a yellowish-brown colour, but when fully grown it becomes dark brown or black. As soon as a bulb makes its appearance on the margin of the umbrella, a branch is given off from the radial canal and joins the ring-canal opposite the bulb. The branch is always given off from the same side of each radial canal, and leaves the canal about the middle of its course on the side of the umbrella. The six lobes of the stomach have now become more conspicuous and extend over the upper part of the sub-umbrella. It is on the sides of these lobes that the reproductive cells develop. The clusters of nematocysts belonging to the first stage still remain, and twelve new clusters appear close to the margin, one midway between every two tentacles. Medusae belonging to the second stage are about 2 m m . in diameter. Third Stage. Eighteen uniform tentacles. (Plate X V I . fig. 4).- This stage commences with the growth of another set of six bulbs, which develop tentacles in the same manner as in the previous stage. The new bulbs are not on the same side of the main radial canals as those belonging to the second stage, but on the opposite side. A new branch leaves each radial canal nearly opposite the junction of the first branch and runs down to the buib on the ring-canal. In this stage each radial canal has two branch canals, one on each side of it, the whole forming a kind of three-pronged fork, with a tentacle at the end of each canal. At this stage the reproductive cells are clearly visible, and are situated along the six lobes of the stomach and arch over the top of the sub-umbrella, forming a star-like pattern of a yellowish-brown colour, hence Forbes's specific name of tbe medusa. The clusters of nematocysts belonging to the first stage, and probably some belonging to the second stage, have now disappeared, and a new cluster is developed midway between every pair of tentacles. The clusters of nematocysts form an excellent mark for |
