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Show 1867-] DR. BOWERBANK ON ALCYONCELLUM SPECIOSUM. 357 code of the sponge. They consist of attenuated rectangulated hexradiate spicula and of rectangulated triradiate ones. There are two well-characterized descriptions of the attenuated rectangulated hexradiate spicula. The first has the radii comparatively short and very stout; this form is exceedingly protean, the full complement of rays being rarely developed. They vary from the form of an inequiacerate spiculum to the completely developed hexradiate one, with intermediate incomplete forms in every imaginable variety. They are dispersed abundantly on the outer surface of the skeleton-tissues, especially near the bases of the diagonal ridges. The varieties of this form of spiculum are described in detail in the ' Philosophical Transactions of the Royal Society' for 1858, p. 309, pl. 25. figs. 24 to 33, and in 'Monograph of British Spongiadee,' vol. i. p. 52, pl. 7. figs. 174 to 183. The second form of attenuated rectangulated hexradiate spiculum is much more constant in its development, an incomplete one being of rare occurrence ; their proportions are more equable and slender than those of the first description. Their radii are comparatively long and slender ; and the basal ray of the axial portion is frequently very much elongated, and has its termination somewhat clavate and more or less spinous, while the distal and lateral rays are usually acute and without spines. These spicula in situ are grouped together in considerable numbers in the interstitial spaces of the skeleton, their positions being coincident, and their axes frequently very nearly touch each other. Their office is apparently the same as those of the larger and stouter description of the same form-that of affording points of attachment to the interstitial membranes, so as to produce innumerable surfaces for the multiplication of the nutrimental membranes of the sponge. They are described and figured in the •Philosophical Transactions' for 1858, p. 310, pl. 25. fig. 34, and in 'Monograph of British Spongiadse,' vol. i. p. 260, pl. 7. fig. 184. The attenuated rectangulated triradiate spicula are not the triradiate stage of development of a hexradiate spiculum; their form is a normal one, and their proportions are distinctly different from either of the hexradiate ones. Sometimes the radii are attenuated and smooth ; but usually the apices of the rays are more or less spinous, and occasionally somewhat clavate. They are not so numerous as the hexradiate forms. They are described and figured in the ' Philosophical Transactions' for 1858, p. 313, pl. 26. fig. 7, and in •Monograph of British Spongiadee,' vol. i. p. 260, pl. 9. fig. 198. The sarcode of this sponge affords two of the most elegant and complicated forms of spicula with which we are acquainted-the trifurcated attenuato-hexradiate, and the floricomo-hexradiate form. The first is not peculiar to Alcyoncellum, as it is also found abundantly in the sarcode of Dactylocalyx pumicea and other siliceo-fibrous sponges. The latter I have never found in any other sponge than the one under consideration. The trifurcated attenuato-hexradiate stellate, spiculum, with a power not exceeding four or five hundred linear, appears as a simple multiradiate spiculum ; but viewed with a power of about 1000 linear |
