OCR Text |
Show 324 DR. J. S. BOWERBANK ON THE SPONGIAD.E. [Mar. 18, attenuato-expando-ternate, rarely patento-ternate; radii short and stout, occasionally cylindrical. Interstitial membranes-tension-spicula acerate, small and slender, few in number, and tuberculated, subcylindrical, the same as those of the dermal membrane. Retentive spicula: attenuato-stellate, radii spinous; cylindro-sphero-stellate, radii spinous; and cylindro-sphero-stellate, radii short and spineless. Colour, in the dried state, ochreous yellow. Hab. Fiji Islands (Sir Everard Home). Museum Royal College of Surgeons. Catalogue of Porifera, part i. I860, p. 127, B. 171. Examined in the dried state. This sponge, 2\ inches in height and 2 inches greatest diameter, is massive but inclined to be cyathiform, and it has apparently been attached by its base to a small oval pebble. In the dried condition, the ternate heads of the connecting-spicuia project beyond the surface of the dermal membrane, imparting an asperated sensation to the touch; this character, it is probable, would not exist in the living sponge. In consequence of the destruction of the greater part of the dermal membrane, the oscula are not very readily to be distinguished ; but the few that are apparent are small and simple in their structure. The dermal membrane, when mounted in Canada balsam and examined with a power of 160 linear, appears almost opaque from the profusion of the tuberculated subcylindrical spicula with which it is furnished ; they are irregularly but very closely packed in a single stratum on its internal surface; an average-sized one measured, length YTTZ incri> diameter ys1 ^ inch. When exceeding the ordinary size, they are frequently somewhat fusiform. The skeleton-spicula are irregular in their size and proportions, and frequently have a sudden decrease of diameter at the distal termination two or three times their own diameter from the apex; and sometimes this contraction may be observed at both terminations of a spiculum. The retentive spicula of the interstitial membranes afford excellent specific characters. The attenuato-stellate ones have their radii always more or less spinous: sometimes their apices only are thus armed; but in their fully developed state the spination extends over every part of them. There are two distinct forms of cylindro-sphero- stellate spicula:-one in which the central sphere is comparatively small, and which has the cylindrical radii spinous; the other in which the central sphere is largely produced, and the cylindrical radii are perfectly smooth. These varieties of sphero-stellate spicula are perfectly distinct and permanent, and never appear to graduate into each other. These stellate forms are very abundant, but they are not readily to be detected in situ without the section being immersed in Canada balsam, in consequence of the great density of the sarcodous tissues. They are mixed together and are irregularly dispersed on the interstitial tissues; and along with them |