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Show 326 DR. J. s. B O W E R B A N K O N SILICEO-FIBROUS SPONGES. [May 13, hexangular pores, lined with a thin layer formed of elongate spicula, placed parallel in bungle in a more or less longitudinal direction round the inner mouth of the pores." The whole of this latter description of the structure of the sponge is remarkable for its inaccuracy. He repeats the fallacy that " the sponge is formed of small spicula," and describes their inosculation, when no such inosculation ever takes place among true spicula. He describes the pores in the total absence of the dermal membrane, evidently mistaking the incurrent orifices of the skeleton for those organs, and then he lines the cavities " with spicula placed parallel in bungle." What may be the mode of disposition of spicula in bungle I must leave my readers to imagine, as I really cannot conceive their arrangement under such circumstances, and especially as I have been totally unable to detect any such lining of spicula within the orifices described by Dr. Gray. The sponge, of the natural size, and slightly magnified, has been beautifully represented in plate 11 of the ' Proceedings of the Zoological Society' for 1858. The natural surface, and the whole of the dermal system of this sponge, have been entirely destroyed, and the pores are therefore unknown to us; but from the regularity of the size and mode of disposition of the incurrent orifices of the skeleton, it is very probable that they were congregated immediately above them. Within the sponge, on the surface of the great cloacal cavity, there are a series of large areas for the discharge of the excurrent streams into the cloaca ; they are very like in size and form to those of the inhalant surface, but they are destitute of the elaborate defences that characterize the inhalant organs. Fig. 4, Plate XXI. represents one of these areas X 108 linear. The form and mode of disposition of the oscular area readily indicates the congregation of the oscula after the same manner as that indicated in Alcyoncellum speciosum, and as exhibited in various species of Geodia. The reticulation-fibre closing this area in the sponge under consideration is remarkably complex and beautiful; each fibre of the oscular area is a compound structure. When a portion of it is immersed in Canada balsam, and viewed by a microscopic power of about 150 linear, it is seen to be a complete cylinder formed of a dense network of siliceo-fibrous structure, produced on the same radial principle as that which prevails in the skeleton of the sponge, but in consequence of the small elongate cylindrical space in which it is developed, its structure is necessarily very confused ; yet the indication of radial fibres within it are sufficiently apparent to assure us of this fact. On the surface, and within the reticulations, there were a few very slender, smooth, acerate spicula which, from the mode of their disposition, are evidently the tension-spicula of the membranous tissues of the sponge. From the external surface of the compound fibre there were a few basal portions of, apparently, hexradiate auxiliary fibres projected; but none of them were developed to the extent of the production of the rectangulated lateral fibres. The external fibres of this beautiful com- |
