1872.] DR. J. S. BOWERBANK ON THE SPONGIADjE. 117 



organs. The skeleton-fasciculi contain comparatively few spicula. 

 They vary considerably in size ; a portion of them are very large 

 and long, frequently exceeding £ inch in length with a diameter of 

 yi^j inch. The smallness of their number is compensated by the 

 intermixture in their fasciculi of the stout long shafts of the ternate 

 connecting spicula ; and the interstices of these larger organs are fre- 

 quently filled in with smaller and more attenuated skeleton-spicula, 

 rendering the whole skeleton firm and compact. 



The recurvo-ternate spicula are comparatively few in number ; their 

 apices rarely reach quite to the dermis ; and, as in other genera in 

 which they occur, their office appears to be to act as defences in the 

 intermarginal cavities. The slender spiculated recurvo-ternate ones 

 are of rare occurrence. 



The basal portion of the sponge is furnished with a few soft 

 flexible radical processes, about f- inch in length. They are appa- 

 rently prolongations of the skeleton-fasciculi of the sponge, and 

 are composed of the same description of spicula, but very slender 

 in their proportions ; among them there were a few small recurvo- 

 ternate spicula, and their ternate heads were frequently in opposite 

 directions. Apparently these spicula are thus present in accordance 

 with the laws of production existing in the animal, and not to assist 

 in any manner in the attachment of the sponge to the spot on which 

 it is based. There were also a few very immature expando-ternate 

 bifurcating spicula, apparently quite as much out of place as the 

 recurvo-ternate ones. The same description of appendages, but 

 stouter and stronger, are found at the base of Tethea hjncurium 

 when the necessities of the animal require their presence. 



Mr. W. Saville Kent has described a mutilated specimen of this 

 species in the 'Monthly Microscopical Journal' for 1870, p. 203, 

 under the designation of Dorvillia agariciformis. The upper portion 

 of the sponge has evidently been torn away from its basal one, causing 

 the part described to assume a form very much like that of an 

 Agaric ; and the under surface of the specimen, having secreted a 

 new dermal membrane, has contributed greatly to the deception that 

 it was a natural form of the animal. The perfect secretion of anew 

 dermal membrane to cover the torn surface is a natural operation 

 that in other sponges frequently takes place within twenty-four hours 

 of the infliction of such a wound; and the new membrane in due 

 course would secrete the stellate spicula which are natural to that 

 organ. The filiform appendages at the base of the specimen figured 

 by Mr. Kent have very much the appearance of being some of the 

 skeleton-fasciculi of the sponge drawn out of the basal portion at 

 the time of its mutilation. 



In treating of the spicula, the author has fallen into the error of 

 describing some of those organs that do not belong to the species 

 under consideration. In the plate accompanying his paper the 

 figures 1 to 9 and fig. 13 certainly belong to his Dorvillia agarici- 

 formis, fig. 13 being a tortuous specimen of a skeleton-spiculum, 

 the normal form of which is straight or very slightly curved. The 

 figures 10, 11, 12, 14, 16, 17, 18, and 19 are certainly extraneous 



