88 



♦ KNOV/LEDGE . 



[Aug. 10, 1883. 



into their minute structure and developmental history, 

 ■without which their real nature could never have been 

 determined. This, then, affords an explanation of how it 

 was that the older naturalists looked upon them as plants, 

 and subsequently regarded them as composite animals of a 

 primitive type. 



The sponges are amongst the most useful and beautiful 

 objects in the Exhibition. Their utility is obvious to 

 everyone in the civilised world, and particularly to a large 

 community of individuals who depend for their living 

 entirely upon the sponge fisheries. 



ijij- 



Fig. S. — Commercial Sponge, showing outgoing cnrrents^of water. 



In modern times the chief sponge fisheries are'confined 

 to the regions around the Bahamas and in the Mediterra- 

 nean Sea, especially in the Grecian Archipelago, and the 

 respective products of both localities are well represented 

 in the foreign gallery of the Exhibition buildings which 

 runs parallel with the aquarium. 





Fig 9 — Outer surfice of d fferei t k i Is f cj i <»(. (nat inl 

 size). A, c„i, olcp^J Voi.oo^ , B, u^ucy^-u^.b ^^uu-c ; C, luhui,- 

 sponge ; D, Bahamas sponge, partly in sections, showing projecting 

 extremities and internal tubular character. 



Let us confine our attention at present to the external 

 forms presented by these sponges, and revert in future 

 communications to their anatomical characteristics and 

 affinities. 



There are thousands of sponges which are of no com- 

 itercial value, either from a strictly utilitarian or an 



aesthetic point of view. The useful sponges, known as the 

 sponges of commerce, belong to one small group, the 

 ySpongia, of which Fig. 8 is an example ; they are divided 

 into two principal subdivisions : 1. The common sponges 

 {Spo7i(jia officinalis) of large rounded or flat forms, soft 

 tissue, convex beneath, and of coarse texture. 2. The fine 

 sponges {Spoiiffia ttsilalissimuin) of concave or cup-like 

 form and tine texture. 





Fig. 10.- 



-Siliceous skeleton of Tenus's flower-basket, 

 Euplectella speciosa. 



It must be borne in mind that we are now speaking 

 merely of the commercial article sponge, and not of the 

 living animal of that name. The former is merely the 

 skeleton of the latter, and consists, in the case of the 

 sponges of commerce, entirely of a horny material 

 called keralose, in the form of fine fibres matted 

 together in such a way as to leave :.umerous large 

 apertures and smaller pores throughout its substance. 

 Fig. 9 shows these differences in texture of some of the 

 principal sponges of commerce. As a rule, the sponges of 

 the Mediterranean are liner than those of the West Indies ; 

 they are, therefore, of higher value for domestic purposes. 

 The usefulness of the sponge must also largely depend on 

 the purity of the fiVires of its keratose skeleton and their 

 elasticity, for upon these qualities do their absorbent 

 powers depend. 



But some of the sponges of commerce live under such 

 adverse circumstances, amidst debris of all kinds, that 

 particles of grit, itc. , become inextricably woven into their 



