OCR Text |
Show 1873.] DR. J. S. BOWERBANK ON THE SPONGIAD.E. 1/ The pitting or areolation of the surface of the sponge is scarcely seen by the unassisted eye; with the aid of a two-inch lens it very closely resembles the pock-marks on the human face. The disposition of the large sphero-stellate spicula in the dermal rind is different from those in any other nearly allied species. Instead of being evenly distributed throughout its substance, they are collected into two dense strata at the outer and inner surfaces of that organ, while the intervening space has comparatively a few only distributed in its substance, and in these comparatively clear spaces the smaller description of subsphero-stellate retentive spicula are abundant. The large sphero-stellate spicula very closely resemble those of Tethea robusta and T. Ingalli; but they are less robust in form than those of the former, and more so than those of the latter species. The greatest diameter of one of the largest size was -4-^r inch. The minute subsphero-stellate retentive spicula with clavated cylindrical radii are exceedingly various in both size and form. In some the radii are slender with very slightly developed bulbous terminations, while others, with the radii quite as slender, have large well-developed distal terminations; and in some the radii are short and stout with a very slightly developed bulb. These minute organs are strikingly different in form from the corresponding ones in any of the nearly allied species, and are certainly the most distinctive of all the specific characters of the species. The average size of the greatest number is TITOO *ncn extreme diameter; but there were a few that measured -g-Jpy inch in diameter. They require a power of about 700 linear to distinctly demonstrate their forms; one of the smallest did not exceed -g-jyVij inch in extreme diameter. The skeleton-spicula vary to a considerable extent in size and in the degree of their fusiformity, so as in some almost to simulate the acerate form. The really acerate and cylindrical ones are of very rare occurrence. The sarcode in all parts of the sponge appears to be very dense. It is most likely that succeeding specimens of this species may not exhibit any of the extraordinary basal appendages that render the specimen figured so singular in its appearance. Such organs appear to be only thrown out when a necessity for them arises from the peculiarities of the locality impeding the safe attachment of the young sponge. Similar appendages are projected from the bases of Tethea norvagica; and there is little doubt that such organs will be observed to be thrown out by other species of Tethea when a necessity for them arises. LEUCONIA GLOMEROSA, Bowerbank. (Plale IV.) Sponge sessile? composed of a closely compressed mass of repeatedly divaricating, slender, compressed, ascending branches. Surface smooth. Cloacae continuous from base to apex of the branch through all its divarications; terminal orifice rarely ciliated; oscular surface coarsely reticulated; rete multispiculous. Oscula large and open. Pores inconspicuous. Dermis-dermal membrane thin, spiculous ; PROC. ZOOL. Soc-18/3, No. II. 2 |