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 PUMICE-STONE SPONGE, 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 spiculse 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 spiculse 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. 



BEFORE 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 Amoebae, 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 



