and Functions of the Sponge. 389 
to be a species of sponge resembling in texture the S. oculata 
{ Beob . p. 29). 
The axis differs so entirely in its nature in different sponges, 
that the living properties observed in one species, ought with 
very great caution to be extended to any other, and naturalists 
may probably take advantage of this difference, in classifying or 
subdividing this numerous and obscure tribe. In some species 
as the S. communis , usitatissima , lacinulosa , fulva , jistulosa , 
the axis consists only of cylindrical tubular horny fibres, which 
dissolve without effervescence in acids, leave no trace when rub- 
bed on glass, and consume like hair when burnt, emitting the 
same horny odour. In others, as the S. compressa , nivea , (a 
small sessile species with triradiate, quadriradiate, and simple 
spicula, to be noticed hereafter, which I have so named from 
its beautiful white colour), botryoides, coronata , pulverulenta , 
the skeleton consists entirely of calcareous spicula, which dis- 
appear before the blowpipe, do not scratch glass, and dis- 
solve with effervescence in nitric, sulphuric, and muriatic acids. 
And in others as the S. cristaia , papillaris , tomentosa , panicea , 
coalita , oculata , dichotoma , stuposa , alcicornis , compacta , jruti- 
cosa , parasitica , hirsuta , palmata , infundibidiformis , ventila- 
brum , hispida , suberica , nodosa , we observe neither the horny 
tubular fibres of the first variety, nor the calcareous spicula of 
the second, but their whole axis is composed of minute siliceous 
tubular spicula, which, in dried specimens, appear drawn toge- 
ther into a longitudinal direction by the hardening of their con- 
necting matter*; these spicula scratch glass, do not dissolve in the 
above acids, nor ^consume by the blowpipe. The siliceous spe- 
cies abound on our shores, the calcareous are more rare, and I 
am not aware that any of the horny sponges has ever been ob- 
served so far north as the British shores. 
Every one is familiar with the softness and remarkable elasti- 
city of the common sponge, S. communis , which is the best ex- 
ample of the horny kind of axis. When a piece of it is brought 
near the flame of a candle, its fibres coil up, melt, and consume 
to a very small, light ash, with a horny smell, like hair ; when 
a portion of it, well washed from sandy particles, is rubbed with 
a wooden instrument on glass, it leaves no perceptible streaks ; 
when thrown into sulphuric or nitric acid, it diminishes in size, 
softens, and dissolves, without effervescence, into a brown pulpy 
