346' T>r GranVs Observatio7is 091 ihe ^'^' 



die, a white brittle dry crust was produced, which was entirety 

 sblu'Me in [water ; on examining the aqueous sokition of this 

 crust, under the microscope, I found that the siUcious spicula 

 had been fused by the aid of the alkaU, and had entirely disap- 

 peared. I have now preserved the spicula of this sponge for 

 more tlian twenty months immersed in nitric, sulphuric, and 

 muriatic acids, and they have suffered no change in their hard- 

 ness, size, transparency or symmetry ; they still scratch glass, 

 and retain their sharpest points unblunted. From the spicula 

 suffering a diminution of their transparency, by the action of 

 heat, it is probable that they possess some animal matter in their 

 composition, which, however, would be very difficult to demon- 

 strate. Mr Children is said to have detected animal matter in 

 the silicious spicula of some species of Tethya, (An. of Phil., 

 vol. ix. p. 431), but his experiments have not yet been made 

 known. I have not had an opportunity of trying their solubili- 

 ty in fluoric acid, and have relied on the above chemical charac- 

 ters, in examining the silicious spicula of marine sponges. The 

 spicula of the Spongia papillaris very much resemble those of 

 the SpongillaJ'riabilis ; they are slightly curved, thickest in the 

 middle, from which they taper gradually to a sharp point at each 

 end, they are of one form though of very different sizes, their length 

 ranges from the tenth to the fifteenth of a line, and their diame- 

 ter from the sixth to the tenth of that of a human hair. They have 

 a vitreous lustre, their texture appears quite homogeneous, and 

 their internal cavity occupies scarcely a third of their diameter. 

 They exhibit neither joints, fibres, nor granular bodies in their 

 substance, nor any kind of motion of themselves, or within their 

 cavity, and appear incapable of contributing to produce the 

 currents of this animal, both from their arrangement round the 

 pores and canals, and from their internal cavity being complete- 

 ly shut at both ends. A number of these spicula lying in the 

 same direction, and close to each other, form a fasciculus, the fas- 

 ciculi which lie parallel to the surface, and form the strong 

 walls of the pores, may be called the hounding ^fasciculi of the 

 pores, to distinguish them from certain others, which project from 

 the margin over the entrances of the pores, and are termed the 

 defending fasciculi of the pores. Both bounding and defending 

 fasciculi are seen also in the course of the canals, and the 



