OCR Text |
Show 24 DR. J. S. BOWERBANK ON HYALONEMA MIRABILE. [Jail. 10, fig. 3 representing a view of the interior of the distal portion of section through the middle of the valve at right angles to the central axis of the oscular tube, by direct light; fig. 4 represents the proximal diaphragm of the same specimen mounted in Canada balsam. The action of these two valvular diaphragms appear to be more or less independent of each other; and the radiating motive fibres, comparatively few in number and very different, in their structure from those of the apical valve, are readily visible in their natural condition when immersed in water or Canada balsam. This is not the case with the motive organs of the more complicated apical valve, which are deeply immersed in the substance of the apical diaphragm, and which cannot be displayed until the internal dissc-pimental structures and the membrane above, which covers them, are removed by the action of a solution of caustic potass for about eight hours-Brander's solution one part and distilled water three parts being of about the required strength. "When these impediments have been removed, the series of motive fibres present a very interesting appearance. The whole censists of numerous spindle-shaped fibres, one end of each being attached to the outer circumference of the corrugated apical area, and the other end to the inner circle of the same part, leaving a circular inner area of transparent membranous structure, the middle of which has the natural orifice of the osculum in its centre, usually in a closed and puckered condition. This parallel radial series of motive filaments, represented in Pl. IV. fig. 5, is doubtless not in its natural condition, the action of the potass having probably increased the motive filaments to two or three times their natural diameter ; so that, when in this state they are forced by pressure or other means through the outer orifice of the osculum, they may have been very readily mistaken for tentacula. The radial motive fibres in the specimen under consideration appear to consist of a strong external membrane filled with dense amber-coloured keratode, apparently the same substance as that of which the corium is composed. The inner membrane, covering the under surface of this radial series of fibres, is apparently a much more delicate tissue than that of the dissepiments of the valvular structure beneath ; and the fragments disrupted by the action of the potass are crowded with minute elongated spiral cells ; but these cells arc not peculiar to this portion of the membranous structures of the corium, as I have found them also in parts of that organ which were not connected with the oscular tubes. Their position, immersed deeply in the sarcodous membrane lining the inner surface of the apical valve, and closely covered by the distal end of the dis-sepimental structures, and also completely immersed in the sarcodous membrane of the inner corium, would seem to indicate them to have some other office in the economy of the animal than that of urti-cating organs as suggested by Prof. M a x Schultze. In the membrane forming the inner diaphragm, and in the parietes of the tubular part of the osculum, there are frequently found cylindro-cruciform and other spicula of the same description as those imbedded in the inner corium. These peculiar forms of spicula |