| OCR Text |
Show 1869.] DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 347 and £ in breadth, which was shaken off a specimen of A. speciosum that I purchased of M r . Geale in January 1867. This fragment of membranous tissue is, comparatively speaking, of considerable thickness, and abounds in amber-coloured sarcode, and there appear to be two well-defined layers of tissue. In the external one there are numerous fasciculi of long slender acerate spicula, the number in each being much too numerous to be counted, and they are very compactly disposed. In one part of the surface the fasciculi radiate from a common basal point, while in two other parts they are nearly parallel to each other. On reversing the specimen the internal layer presented a rudely cellulated appearance, abounding in sarcode, in which two of the most characteristic auxiliary spicula of Alcyoncellum were deeply imbedded-one of them, an incompletely developed stout rectangulated hexradiate interstitial spiculum, exactly represented by fig. 181, plate 7, M o n . Brit. Spongiadse, vol. i., and the other a rectangulated hexradiate one, represented by fig. 198, plate 9, of the same work; and there is also a slender rectangulated hexradiate spiculum, like the one represented by fig. 10, Plate XXIV., illustrating the present paper. With these indications, I think there is little doubt that the structure I have described is a portion of the dermal system oi Alcyoncellum, and that, when we obtain a specimen in the condition in which it is taken from the sea in the living state, we shall find the beautiful skeleton entirely enveloped by such a dermal membrane as I have described from the fragment in m y possession. Should these ideas prove correct, a slight addition would become necessary in m y description of the specific characters oi Alcyoncellum speciosum in the Proc. Zool. Soc. for March 28, 1867, p. 354, line 12 of the specific character, where the dermal membrane is described as "unknown," in place of which should be added, " Dermal membrane abundantly cpiculous ; spicula acerate, long and slender, fasciculated ; fasciculi compact, disposed in radiating or parallel groups." In this description of the dermal structure of the sponge, it will be observed that there are no connecting spicula present; and we may therefore infer that the genus Alcyoncellum is not furnished with an expansile dermal system as in the massive rigid skeletons of Dactylocalyx and other similar siliceo-fibrous sponges. The fistular construction of the skeleton in Alcyoncellum renders such a provision as an expansile dermal system quite as unnecessary as it would be in the genus Grantia and numerous other fistulous sponges. I obtained also two fragments of the skeleton in which there was a considerable quantity of sarcode; and immersed in this substance numerous rectangulated triradiate and rectangulated hexradiate spicula of the slender descriptions were intermixed without any apparent arrangement. Every one of the interstices of the fibrous skeleton, large or small, was abundantly supplied with them. The well-washed specimens of the sponge now so numerous afford no adequate idea of the profusion of these descriptions of spicula that exist in the sponge in its natural condition. There were also numerous indications of the presence of floricomo- |
