Structure of some Silidous Sponges. S45 



observe the whole texture to consist of polygonal pores systema- 

 tically, though somewhat rudely, constructed of loose fasciculi of 

 minute transparent, colourless, pointed, and slightly curved, 

 needles, entirely imbedded in a viscid yellowish translucent mat- 

 ter ; and we cannot fail to be convinced, on the slightest inspec- 

 tion, that the form, size, composition, and arrangement of these 

 needles have a perfect relation to the function they fulfil of form- 

 ing and defending these passages, and that the spicula could not 

 possibly have been pushed into this dense systematic order round 

 the pores, by worms, insects or animalcules piercing and traver- 

 sing the soft surface, nor have we the least acquaintance with 

 any inhabitant of the ocean, capable of secreting such singular 

 crystalUne bodies, and of piling them up into so complicated a 

 fabric for the protection and development of its ova. We shall 

 see further proofs of this in the anatomy of the soft parts of this 

 animal. By allowing a portion of this sponge to remain a few 

 hours in a watch glass with nitric, sulphuric, or muriatic acid, 

 the soft connecting matter dissolves, and the spicula fall sepa- 

 rate to the bottom, without having suffered any change in their 

 size, form, or appearance. If we rub these spicula with a wooden 

 or glass rod against the bottom of the watch glass, after pouring 

 oflp the acid, and washing them with water, we feel distinctly, 

 that they are of a hard quartzy nature, and that they cut the 

 bottom of the glass; with a lens we can perceive the minute 

 streaks they produce, when they are rubbed on the surface of 

 smooth glass. At a red heat the spicula suffer no change, but 

 when they are kept at a white heat for a few minutes by the 

 blowpipe, they become semiopaque and white, and some of them, 

 are observed to dilate and burst. When the spicula have beea 

 simply dried, we can perceive by the microscope a distinct cavi- 

 ty within them, extending their whole length, and completely 

 shut at both extremities; probably some fluid matter within that 

 cavity prevents it from being so distinctly seen in the recent 

 spicula. To try in a more satisfactory manner the silicious na- 

 ture of these spicula, I removed the animal matter by means of 

 the blowpipe from a portion of the papillaris^ and formed the 

 remaining dried axis into a paste, with three or four times its 

 bulk of pure potassa. On exposing this mixture of spicula and 

 potassa, on a tin plate for a minute or two to the flame of a can- 



