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Show 348 DR. J. S. nOWERBANK ON SILICEO-FIBROUS SrONGES. [May 13, hexradiate stellate spicula amidst the sarcode; but the density of that substance rendered them almost invisible. In some of the specimens that I have recently examined, I have observed a remarkable habit of some of the rectangulated hexradiate spicula-that is, that one of the axial radii is more or less sheathed or enveloped by branches of skeleton-fibre, so as to give the spiculum a firm and permanent position ; and this appears to be more frequently the case with those which are projected into the inhalant areas. This attachment of the spiculum by the fibre is not a fusing of one into the other, as when two fibres touch each other, but it is simply a partial envelopment of a portion of one of the radii, so as to give it a secure basal point of attachment to enable it to perform its appointed office of sustaining the interstitial membranes of the sponge under peculiar circumstances, or to protect the orifice over which it is projected. The portion of the ray thus enveloped may frequently be traced within the enveloping fibre. It is a very remarkable fact that none of the other auxiliary spicula, although large and strong, are ever seen to be thus agglutinated by the fibres. This singular habit of the rectangulated triradiate spicula assimilates them in their office in some measure to the auxiliary fibres in the skeletons of Dactylocalyx and Iphiteon. Although thus agglutinated by the fibre, they really form no essential part of the true rigid skeleton of the sponge, but are in reality neither more nor less than auxiliary supports to the interstitial membranes under certain conditions. APPENDIX (May 25, 1869). Since the preceding portion of this paper was written, I have seen several specimens of Alcyoncellum speciosum that were sent home in spirit in the condition they were in when taken from the sea. There were five specimens, all as nearly as possible in the same condition. They were of a dark dirty colour, and looked very much as if they had been dipped into thin mud and then dried. On mounting slices from the surface, and fragments of the entire structure of the skeleton, this dirty-looking substance, when immersed in Canada balsam, proved to be the remains of the membranous and sarcodous tissues ; but I could not find any traces of a dermal membrane, such as might naturally be expected to be present if the sponges were in a living condition when taken from the sea. The largest specimen in spirit had a considerable portion of one side of it entirely deficient of the sarcodous and membranous structures that were abundant in the other parts of the specimen. This circumstance, the deficiency of dermal membrane, and the condition of the sarcode and interstitial membranes in the whole of the specimens, appears to lead to the conclusion that these specimens were dead sponges in a state of partial decomposition, and that we have yet to acquire specimens which were in the living state when brought up from the bottom of the sea. Although not in so satisfactory a condition as may have been desired, they were still in such a state of preservation as to afford some interesting points of information regarding the structural pecu- |
