OCR Text |
Show 1875.] DR. J. S. BOWERBANK ON THE SPONGIADcE. 289 are projected at right angles to the fibre into the areas, frequently in considerable numbers ; a power of about 300 linear is required to exhibit them in situ in a satisfactory manner; their length rarely exceeds ^fc$ inch. The acuate skeleton-spicula are distinctly different in their proportions from those of the dermis; their diameter is twice that of the dermal ones. A full-sized one measured OTJW m c b hi diameter. Since the above description was written I have examined another specimen of this species, sent to me from the Straits of Gaspar by Commodore Parish. It is, in its external and anatomical characters, very like the type one, but rather larger and more strongly developed. A remarkable circumstance attending this specimen is that it has two very interesting radiate animals seated upon it, the small or basal arms of which are so interwoven amidst the branches of the sponge as to render it impossible to disentangle them without the destruction of the radiate animals, wh'le the larger and longer arms for entangling their prey are thrown out above in every direction. Their mode of anchoring themselves on the sponge is an interesting fact in their natural history. HALICHONDRIA RIGIDA, Bowerbank. Sponge massive, sessile. Surface very rugged and uneven, full of ridges and depressions. Oscula simple, dispersed. Pores inconspicuous. Dermal membrane pellucid, spiculous; tension spicula acuate, the same diameter and nearly the same length as those of the skeleton; retentive spicula bihamate, simple, and contort, rather numerous; and bidentate equianchorate, small, but rather stout, not numerous. Skeleton-rete multispiculous, very wide and open, irregular ; areas very variable in size; spicula purely acuate, rather short and stout. Interstitial membranes sparingly spiculous ; spicula same as those of the dermis. Colour, in the dried state, dull green. Hab. Straits of Malacca (Commodore Parish, B.N.). Examined in tbe dried state. I obtained this sponge from my friend Commodore Parish. It is from the Straits of Malacca. It is 2| inches long, 1 inch wide, and rather exceeds half an inch in average thickness. The dermal membrane is rather sparingly furnished with tension-spicula. There is very little difference between these spicula and those of the skeleton; the latter are rather the longer of the two ; their diameter is about the same. In consequence of the open structure of the skeleton-rete there are a considerable number of surreptitious spicula of various forms amidst the tissues of this sponge ; and fragments of some of these are occasionally incorporated in the skeleton-fibre, as in a Dysidea. The spicula in the fibre are numerous and closely compacted, and the areas very wide, but by no means equal or regular in either form or size. The bihamate retentive spicula are not very abundant; they are rather slender; and the simple and contort forms are about equal in number, and PROC. ZOOL. Soc-1875, No. XIX. 19 |