Sponges. 55 



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

 tion 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 particles each bearing a vibrating hair , which it lashes on the 

 current, and a transparent filmy skirt, with which it catches any food 

 that may pass. 



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

 prevent 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 5 a few have lost 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 pe- 

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

 The flinty sponges [Silicea] are the most 

 numerous 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 23, see p. 73) under which, 

 however, will be found in such case a crab 

 using it as a protective covering. 



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. 1 1 S) ; over all the rest the dark, 



slate-coloured flesh forms a continuous film. *'% 159 - S ? me specimens 

 T , . i , . j i j. . , , . , of buconrapfuinus, attached 



It is obtained by diving, dredging, or harpoon- to * piec / of ro ; k at the 



ing with a long trident; the principal markets left hand, 



are at Trieste and Paris. Of the different kinds 



the finest and most costly is the Levantine sponge (Euspongia offici- 

 nalis] which, in its varieties, 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 (Hippo upon gia 

 tquina, 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 



