THE SHOEES OF BRITAIN. 53 



brown woolly substance, perforated by innumerable 

 pores in all directions, and having in addition, wide 

 canals communicatincr with each other, and terminat- 

 ing in round holes or mouths on the surface. But if 

 we take a small portion of the substance, and place 

 it under a common magnifying lens, we shall see that 

 it is composed of shining, horny, nearly-transparent 

 fibres, which, by uniting with each other at all angles 

 and distances, form a loose and very irregular net- 

 work. Now, when in a living state, every fibre was 

 enclosed in a coating of thin, clear jelly, which 

 formed the living animal, the horny fibres consti- 

 tuting, as I have intimated above, only the skeleton. 

 Imbedded in the substance of many species, some 

 British ones, for example, are found spicula, or 

 needle-like bodies resembling crystals, of pure flint, 

 varying much in shape in various kinds, while other 

 species have similar crystals of lime. Where these 

 occur in considerable numbers, the Sponge does not 

 possess elasticity : it may be crushed, but it will not 

 regain its original form. It is a singular fact, that 

 Sponges of these three different kinds are sometimes 

 found growing close to each other, and all alike 

 nourished by the same simple fluid, pure sea-water ; 

 yet they elaborate therefrom products so diiSerent as 

 horn, flint, and lime. The animal nature of Sponges 

 is not easily to be detected : it has been asserted, 

 indeed, that no indication of sensation has ever been 

 perceived in them when living, even though violence 

 in many modes has been offered to them ; though 

 beaten, pinched with hot irons, cut or torn, or sub- 

 jected to the action of the strongest acids. This, 



