72 



It is of a dull ochreous yellow colour, and has the surface much 

 asperated by the projection of numerous stout sandy fibres. The ex- 

 current canals are large and few in number, and have their termina- 

 tions occasionally projected beyond the surface. The fibre of this 

 species varies considerably in its character. The larger and coarser 

 portion is constructed of grains of sand of various sizes, encysted se- 

 parately in the substance of the horny structure, as described in the 

 preceding part of this paper in treating of the structure of Duseideia 

 Kirkii. Among the arenaceous fibres there are others of a fistulose 

 structure, which have few or none of the grains of sand imbedded in 

 them. In the largest of the arenaceous fibres the grains of sand are 

 accumulated in such numbers, and so closely built together, as fre- 

 quently to render the fibre nearly impervious to light, as represented 

 at figure 12 j but in the smaller ones, as seen in fig. 13, they are few 

 in number, and disposed in nearly the centre of the fibre. A few spi- 

 cula are occasionally found imbedded among the grains of sand or at- 

 tached to the surface of the fibre, as represented at figures 12 and 13. 

 The tubular fibres are smaller than the arenaceous ones, but originate 

 from them and freely anastomose with them. The fistulose cavity is 

 large, continuous, and contains an abundance of spicula of a variety 

 of sizes and forms. In the smallest of these fibres the spicula are 

 usually lying in a longitudinal direction ; but in the larger ones they 

 are disposed without any apparent order, and assume every possible 

 direction. Sometimes the small tubular fibres suddenly expand to 

 twice or thrice their original diameter, and again contract to their for- 

 mer size, the cavity expanding in proportion, and containing a great 

 accumulation of spicula ; at other times the tube becomes attenuated, 

 and terminates by attaching itself to a grain of sand, of eight or ten 

 times its own diameter, around which it spreads its horny structure 

 until the grain is entirely enveloped by it, and firmly supported as it 

 were upon a pedestal. These isolated grains are probably but the 

 first stones in the foundation of the future large arenaceous fibres. Oc- 

 casionally we find a few small grains of sand imbedded in or attached 

 to the external surface of the fistulose fibres, and then the spicula are 

 fewer in number in their immediate neighbourhood, but usually they 

 are without grains of sand. These fibres also appear to be destined 

 to perform another important office in the economy of the animal ; for 

 in many of the Brighton specimens of this sponge I observed ova or 

 gemmules, of various sizes, imbedded in the parietes of the tubes ; 

 some of them projecting from the inner surfaces towards the centre of 

 the fistulose cavity, but the greater number were projected from the 



