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Show 1885.] DR. HUBRECHT ON A NEW PENNATULID. 513 whole colony feel hard and rigid when handled. Whereas in the stem these calcareous needles-for such they proved to be on microscopic examination (see fig. 14)-are in no way raised above the common level (faint transverse wrinkles being, however, observable), their aspect on the rhachis is considerably different. Here they unite to form projecting polyp-cells, which have the aspect of shields or scales (figs. 4 & 5), but which merge into the proper surface of the rhachis. These apparent scales are moreover provided with two projecting points, well marked in the different figures, and also wholly consisting of the same needle-like spicules ; whereas they are arranged along the rhachis in what appeared to be faint spirals, ascending from the concave (ventral) side towards the convex (dorsal) one, and directed forwards, i. e. towards the extremity of the scaleless stem. Figs. 6 and 7 show that there are no continuous spirals, but that along the median line of the convex surface the rows of large scales are interrupted by a longitudinal bandof very minute scales, answering, however, to the same type, but apparently without any projecting polyps, and which, after Kolliker, may well be called zooids (vide infra). At the top of the stem the polyp-cells have not yet acquired the definite and characteristic shape which is indicated in fig. 5. The few which may here be noticed have a more circular, nipple-like aspect; those just below the top are intermediate between the lateral and the top ones. The characters above enumerated are sufficient to raise a strong suspicion that the colony in question is a Pennatulid. Longitudinal and transverse sections of stem and rhachis will enable us to test this supposition by means of the internal anatomy. The general impression from a transverse section through the rhachis is this, that the colony is much less massive and solid than the external appearance and the rigidity would lead us to suppose. We notice a spongy arrangement of large-sized spaces, separated by a system of thin septa and trabeculae (figs. 1 3 & 8), the arrangement of which we shall hereafter have occasion to examine in detail. When touched with the forceps the material that builds up this internal framework is found to be stiff and brittle, and microscopic examination shows that this part of the ccenenchyma is also laden with very numerous calcareous spines (fig. 14), similar in shape to those found in the exterior investment. These spines, though of uniform shape, are of different size. The organic ground-substance in which they are imbedded is moreover stiff and horny, and is dissolved in caustic potash. Together with the calcareous spicules, it gives to the internal framework its rigidity. In a section through the stem (fig. 12 and woodcut, p. 515, figs. 1 & 2) the arrangement of these septa is seen to be more regular, the free spaces are very symmetrically arranged, and the outer wall is in comparison thicker than in the rhachis. Towards the inferior extremity of the stem there is only one transverse septum, dividing its inner space into a dorsal and a ventral half. This septum is seen in a longitudinal section (perpendicular to its plane) in fig. 9. It appears gradually to split into two parallel |
