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THE SCIENCE OF LIFE. 



are brought within reach of the bioplasts. (Fig. 72.) 

 The Sponges are divided into three orders : Horny, 



FIG. 72. Sponge in action. 



Silicious, and Calcareous sponges. In the first order 

 (Keratosa) is found the sponge of commerce, which owes 

 its value to the fineness of its fibers and the absence of 

 silicious spicules. Some sponges of this order have 



YIG. 73.. a. Portion of Halichondria (?) from Madagascar, with spicules projecting 

 from the fibrous network, b. Silicious Spicules of Pachymatisma. 



flinty spiculse of various shapes, as pins, clubs, crosses, 

 hooks, and anchors. (Fig. 73.) The silicious sponges 



