52 HALF AN HOUR WITH SPONGES. 



do you perceive ? That the substance to which you 

 have always given the name of sponge, is only the 

 skeleton, in reality, of the entire animal. Inside the 

 large and small openings, and outside the whole 

 skeleton, is a gelatinous substance resembling white 

 of egg, which is sometimes faintly coloured. This is 

 the real " sponge flesh." It frequently has distri- 

 buted through it minute spicules, as if for support ; 

 whilst these spicules interlace, and, with the horny 

 fibre, make up the body of the skeleton that which 

 when dried always goes by the name of " sponge." 

 When this gelatinous flesh, commonly called sarcode, 

 is examined, it is seen to possess a granular structure. 

 These grains very much resemble the simple organism 

 one of the very lowest in the animal kingdom 

 which is common in stagnant ponds, the little 

 Amoeba. In fact, the " sponge-flesh " may be re- 

 garded as a colony of these amoeboid animals united 

 together, just as a coral reef is composed of a colony 

 of zoantharians. You will observe that both in 

 this gelatinous exterior and the internal skeleton 

 there are certain openings, large and small. In the 

 species we have mentioned the commonest thrown 

 ashore after a storm you see the larger orifices 

 running in rows down each branch .(see Fig. 25). 

 Of these two kinds of perforations, the larger are 

 termed " oscula," and the smaller go by the com- 

 moner name of " pores." The former are " ex- 

 halent," that is, they throw out wasted matter and 

 excreted food ; whilst the " pores " are " inhalent," 



