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Show 1875.] DR. BOWERBANK ON SILICEO-FIBROUS SPONGES. 503 5. A Monograph of the Siliceo-fibrous Sponges. By J. S. BOWERBANK, LL.D., F.R.S., F.Z.S., &c-Part IV. [Received June 8, 1875.] (Plates LVI. & LVII.) Further observations on the anatomy and physiology of A L C Y O N C E L L U M SPECIOSUM, Quoy et Gaimard. (Plate LVI.) Euplectella aspergillum, Owen, Trans. Zool. Soc. iii. p. 203. Euplectella cucumer, Owen, Trans. Linn. Soc. xxii. p. 17, pl. 21. In m y former observations on the anatomy and physiology of this singular and very beautiful Sponge, published in the Society's ' Proceedings' for 1867, p. 351, and for 1869, p. 346, I have stated that I had tried in vain to obtain a knowledge of the dermal structures of this sponge. In m y paper of May 13, 1869, I detailed m y examination of a very small fragment of what appeared to me to be the dermis ; and subsequent examinations of other minute pieces of a similar description have confirmed the opinion I had then formed. Since 1869 I have made every possible effort to solve the problem of its dermal structure, but without any satisfactory result. What my best efforts could not attain, the good fortune of m y friend Dr. John Miller, F.G.S. & c , has achieved by the acquisition of a specimen in which the skeleton of the dermal organization is in a perfect state of preservation ; and I am much indebted to him for having kindly presented me with part of this beautiful and valuable specimen for examination and description. No portion of the sarcodous structures remain on any part of the specimen. These tissues appear to have been removed from the dermis by gradual undisturbed decomposition, leaving its siliceous skeleton in situ in a remarkably perfect state of preservation; and not only so with regard to the dermal skeleton, but the rigid skeleton of the sponge appears to be precisely in the same state as when living, every portion of it appearing to occupy its appropriate position, so as to enable us to render a much more correct account of its general structure. Hitherto the only specimens available for examination have been in such a well-washed condition as to render it extremely difficult to determine the true positions of the unattached spicula found among those of the rigid skeleton; and in many cases the rectangulated sexradiate spicula of the dermis and the floricomo-sexradiate ones have evidently been washed into the interstices of the rigid skeleton. On examining a portion of the sponge presented to me by Dr. Miller, mounted iu Canada balsam, with a power of 100 linear, we find that at the inner surface of the specimen the large primary fibres of the skeleton are strikingly distinct; and in the irregularly shaped interstices of their reticulation there were numerous stout rectangulated sexradiate spicula, and a large number of the same form of various degrees of tenuity ; their positions were mostly un- |