Sponges. 55 



into the outflowing current from the large holes (oscula). At the junction 

 between the two systems of tubes are the most vital organs of the sponge, 

 little swollen cavities of microscopic size walled in with tiny living par- 

 ticles , each bearing a vibrating hair , which it lashes on the current, 

 fcnd a trasparent filmy skirt , with which it catches any food that 

 ' may pass. 



All this labyrinth of canals and cavities is living, soft flesh. To pre- 

 vent it falling a ready prey to the first hungry animal that passes, it 

 is set through and through with little flinty needles or thorns. A smaller 

 group of sponges has its spines of chalk, to serve the same end. A very 

 large number of the flinty sponges cement their spines together with 

 the horny substance already referred to; a few have the flinty spicules 

 entirely, and, to withstand better the shocks of the waves have replaced 

 them by the more elastic cement. The net-like skeletons of this last small 

 group form the sponges bath-sponges, toilet-sponges, and the rest, with 

 which we habitually associate the name. The animals in which they were 

 contained are killed by exposure to the air, and then removed by repeated 

 washing. 



The chalky sponges (Calcarea) are mostly small, and either grey or 

 white. A fair type is the Sycon raphanus , of which a variety pecu- 

 liar to the Aquarium grows thickly on the walls of its tanks (Fig. 159). 

 The flinty sponges (Silicea) are the most nume- 

 rous and varied; to these belong in the Aquarium 

 the orange-coloured branches of Axinella (Fig. 

 120), the yellow balls of Tethya (Fig. 119); also 

 the apparently free moving Suberites (tank 53, 

 see p. 73) under which , however, will be found 

 in such case a crab using it as a protective co- 

 vering. 



The sponge of commerce is of the form we 

 know in its domestic relations, but in life shows 

 on its surface the largest only of its numerous 

 holes (Fig. 118); over all the rest the dark, slate- 

 coloured flesh forms a continuous film. It is obtained Fig- 159. Some specimens 

 i j. . j j . , . .,v i of Sycon raphanus. attached 



by diving , dredgig , or harpooning with a long to p iece O f rock at the 



trident; the principal marktes are at Trieste and left hand. 



Paris. Of the different kinds the finest and most 



costly is the Levantine sponge (Euspongia offidnalis} which , in its va- 

 rieties, extends on all the eastern Adriatic and Mediterranean shores. It 

 is not found west of Naples, and on the Italian coast no sponges occur 

 in remunerative quantity , though quite recently some beds have been 

 discovered near Sicily. The harder Zimocca sponge (Euspongia zimocca), 

 from Asia Minor and Egypt , fetches about one tenth of the price , as 

 does the large coarse horse sponge (Hippospongia equina), found in all 

 the Levant and extending along Africa to the Straits of Gibraltar; it is 

 honey-combed with wide holes. Of the last genus (Hippospongia) are the 

 American glove sponge and sheeps-wool sponge ; their hard- 

 head is related to the European Zimocca, while their velvet sponge 

 and grass sponge are independent species. The Bahamas and Carib- 



