OCR Text |
Show 330 DR. J. S. BOWERBANK ON THE SPONGIADcE. [Mar. 18, by a thick layer of indurated sarcode. The distal ends of these organs are protected by an irregular fringe of small fusiformi-sub-acuate or acerate external defensive spicula. These conditions of the dermal crust and the intermarginal cavities unmistakably indicate the congregation of the pores on the dermal membrane. The oscula are few in number; they are congregated in a slightly depressed area; the largest does not exceed the tenth of an inch in diameter. The connecting-spicuia are comparatively small and few in number; they do not penetrate the dermal crust, but their ternate terminations are closely applied to the proximal surface of the stratum of indurated sarcode immediately beneath the dermal crust. The greater portion of them are subexpando-ternate; but some of them are nearly patento-ternate. They vary in length from about 3^ to -^ inch. The fusiformi-acerate spicula of the skeleton are very numerous; they average ^V m c n in length, while the fusiformi- acerate tension ones, which are abundantly intermixed with them, seldom exceed jfo inch in length. The two forms of cylindro-stellate retentive spicula differ considerably in size. Two of them, imbedded closely adjoining each other in the interstitial membranes, measured from the distal extremities of their opposite radii as follows:-the largest one yy1^ inch extreme diameter, the minute cylindro-stellate form -g-g-^-g- inch extreme diameter, while the radii in each were nearly of the same diameter. They do not appear to pass into each other by variations in the proportional length of the radii, %ut each variety seems to adhere to nearly the same dimensions ; neither do they appear to occupy particular positions on the tissues, but are irregularly dispersed over the interstitial membranes. The adult ovaries are perfectly globular, or very slightly depressed at the foramen; they measure ^-g-g- inch in diameter; the cuneiform spicula of which they are composed are comparatively large, and the distal extremities are strongly developed and are very angular. Ovaria in all stages of development were present in abundance in all parts of the interior of the sponge. The structural peculiarities of the ovaries in this species are more than usually beautiful when viewed with a power of about 700 linear. The distal termination of each spiculum in the adult specimens presents an acutely angulated stellate appearance, closely resembling a five- or six-rayed star, the radii of which are acutely conical, cemented together by translucent silex, so that each ovarium resembles a beautiful crystal sphere, regularly ornamented with innumerable minute stellae. Many years have passed since I first examined this sponge, but I have never been fortunate enough to meet with another specimen. TETHEA HISPIDA, Bowerbank. (Plate XXXI.) Sponge sessile (?) ; surface strongly and thickly hispid. Oscula and pores inconspicuous ? Dermis abundantly spiculous ; spicula disposed at right angles to the surface, uniformly crowded together; superfusiformi-subovo-spinulate, very minute, forming a secondary series of defensive spicula. Primary series of defensive spicula super- |