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Show 1873.] DR. J. S. BOWERBANK ON CEYLONESE SPONGES. 29 when examined microscopically. It is produced partly by the extension of the primary lines of the skeleton, and partly by the projection of single spicula, of the same size and form as those of the skeleton, through the dermal membrane. I could not detect either oscula or pores on any parts of the external surface ; and it is very possible that inhalation takes place on the outer surface, within the folds of the plications of the skeleton-tissues, and that the excur-rent streams are ejected on the inner surface in a similar manner. A n d this mode of inhalation and of exhalation is the more probable as these plications are distinctly visible to the unassisted eye for about half an inch downwards on the outer surface, and to twice as deep on the inner one. The plications are composed of closely packed parallel thin plates of the sponge-tissue, all disposed at right angles to the dermal surface ; but this regular arrangement of the skeleton-tissues does not seem to obtain beyond the limits stated above ; the lower portions of the skeleton-structure appear to meander in every possible direction. The dermal membrane does not spread uniformly over the surfaces of the sponge, but it appears to follow and encase the plications of the skeleton ; and I could obtain a view* of it only on the surface of the plates, and on the terminations of the defensive prolongations of the primary lines of the skeleton projected from the external surface of the sponge, when mounted in Canada balsam, and with a power of about 80 linear. On those parts it was abundantly supplied with the slender tension-spicula, intermixed with which were a considerable number of the larger or skeleton-spicula. The skeleton is very strongly developed. The primary lines frequently throw off branches which pursue their course in lines parallel to the parent braneh. This habit, in conjunction with the great irregularity in the size and mode of disposition of the secondary lines of the skeleton, often produces a considerable amount of confusion among the skeleton-structures. I have never observed the same singularly plicated form of the skeleton-tissues in any other species oi Isodictya with which I am acquainted. Mr. Holdsworth, in his letter to m e, writes :-" The dark, thick, cup-shaped sponge with undulated margin is not uncommon on the large pearl-bank in from 6| to 9 fathoms; and I have met with it once or twice on rough ground on other parts of the coast; it is usually attached to some bit of rock, and is always, when alive, of a uniform bright orange-colour. It turns black an hour or two after being taken out of the water. The largest specimen I have seen was about as large again as the one you have. The general shape and colour are always the same." HALIPHYSEMA TUBULATUM, Bowerbank. (Plate VII.) Sponge massive, sessile. Surface minutely mamillated. Oscula and pores inconspicuous. Dermal membrane obsolete. Skeleton composed of numerous single and separate cylindrical tubuli radiating from the base to the surface of the mass; tubuli closed, termi- |