590 GROWTH OF SPONGES. 
Polyphemus himself might have filled its depths with the ruddy wine which he loved, and 
failed to empty the huge vessel at a draught. 
The substance of this enormous Sponge is porous, rather stiff, and without much elasticity. 
It yields but slightly to pressure, and almost feels to the touch as if it had been made from 
cork. 
This is one of the exotic Sponges, being found only in the hotter seas. In general shape 
it has some resemblance to the Funnel-sponge already described, but is of much coarser texture, 
and, save for its gigantic size, is not nearly so attractive. 
In the PumricE-STONE SponGk, we have an admirable example of the flinty structure 
developed to the utmost degree. The framework is wholly composed of flinty spiculee, all 
fused together, and forming a highly porous mass, which at first sight resembles a madrepore 
rather than a true Sponge. It has not the least elasticity, but is as hard and as stiff as if it 
had been carved from stone. On account of its extreme porosity, it is very light, seeming to 
weigh not more than a piece of cork of the same size. 
The whole surface, above and below, is plentifully sown with pores, which have a lovely 
effect under a magnifier, when the sunbeams fall on the glittering spiculze of which the mass 
is composed. A number of the large apertures appear on both sides, and all converge towards 
the centre. The general shape of this remarkable Sponge is cup-like, but exceedingly shallow, 
and on the inside it is tolerably smooth, becoming rougher and deeply grooved on the outer 
surface. It has a peculiarly rough feel to the touch, almost exactly resembling the well-known 
rasping effect produced by rubbing pumice-stone upon the skin; and it is in consequence of 
this resemblance that it has gained its popular title. 
The peculiarities of this very beautiful Sponge consist in the following distinctive char- 
acters, the most remarkable of which is its being formed entirely of silex, the reticulate 
structure of the mass being composed of transparent, glassy tubes, the silex forming the mass 
itself, and not, as in other instances, arranged as spiculze in the horny membranes ; conse- 
quently, it is perfectly rigid and sonorous when struck. 
When viewed under a microscope of about seventy-five diameters, the net-like meshes are 
seen to be composed of beautiful glassy tubes, uniting one with the other in every direction, 
the external surface of the cylinders having a rugged aspect. The newest or last-formed 
portions appear to emanate from centres, and at certain distances from spherical knobs, from 
which straight tubes again arise, thus forming the net-like mass. 
BeEForE taking leave of these interesting beings, we must glance rapidly at the method by 
which they distribute themselves so widely and increase with such marvellous rapidity. 
It will be remembered that the soft animal matter of which the true Sponge is formed is 
composed of multitudinous bodies which closely resemble the Amoebze, and many of which are 
furnished with thread-like cilia. In certain months of the year, which in moderate climates 
are generally found to be October and November. a vast number of very minute yellowish 
particles are to be seen studding the body of the Sponge. They are not often seen near the 
surface, but are gathered plentifully within its multitudinous cells. Small as are these yellow 
particles, they are formed of many eggs, or ‘“‘gemmules,’’ as they are called, of the Sponge, 
which gradually increase in size, and at last are expelled from the larger orifices, and thrown 
at random into the wide sea. 
There they are, flimsy, minute, shelterless, feeble, and apparently helpless. Small, how- 
ever, as they may be, they still possess the power of transporting themselves through the 
water by means of the cilia with which their bodies are abundantly studded. Their shape is 
very like that of a pear; and as they are wholly covered with cilia, except the narrow end, 
it is evident that their larger end must always be in front. They lead a free life for several 
days after their expulsion from the parental home; and even in this early stage some indica- 
tions of the future framework are to be seen. 
After the lapse of some little time, these gemmules meet with some object which affords 
them a suitable resting-place, and accordingly affix themselves to the spot, from which they 
