DUSEIDEIA. 189 



them, and freely anastomose with them. The fistulose cavity 

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

 variety of sizes and forais. In the smallest of these fibres, the 

 spicula are usually disposed in a longitudinal direction, but in 

 the larger ones they are disposed without any apparent order, 

 and assume every possible direction. Sometimes the small tu- 

 bular fibres suddenly expand to twice or thrice their original 

 diameters, and again contract to their foi-mer size, the cavity ex- 

 panding in proportion, and containing a great accumulation of 

 spicula ; at other times the tube becomes attenuated, and termi- 

 nates by attaching itself to a grain of sand eight or ten times its 

 own diameter, around which it spreads its horny structure un- 

 til the grain is entirely enveloped by it, and firmly supported, 

 as it were, upon a pedestal. These isolated grains are proba- 

 bly but the first stones in the foundation of the future large are- 

 naceous fibres. Occasionally, we find a few small grains im- 

 bedded in or attached to the external surface of the fistulose 

 fibres, and then the spicula are less in number in their imme- 

 diate neighbourhood ; but usually they are without grains of 

 sand. These fibres also appear to be destined to perform ano- 

 ther important office in the economy of the animal, — for in 

 many of the Brighton specimens of this species I observed ova 

 or gemmules of various sizes imbedded in the parietes of the 

 tubes ; some of them projecting from the inner surface towards 

 the centre of the fistulous cavity, but the greater number were 

 projected from the outer surface of the fibre in all degrees short 

 of absolute separation. When viewed as ti-ansparent objects, 

 with a power of 300 linear, these gemmular bodies have a large 

 opaque nucleus, of a somewhat granulated character, which fills 

 the whole of its interior, and is surrounded by a thin horny- 

 looking shell or coat. 



" The spicula are exceedingly variable in size and form. The 

 greater portion of them are slightly ciu'ved, and attenuating to- 



