. Comparative anatomy and physiology. Chap. SPICULES OF SPONGES. 279 sponges), or the organic substance becomes impregnated with calcareous salts (calcareous sponges), or with siliceous (siliceous sponges). Considerable variations are, moreover, to be seen in the extent to which this impregnation takes place, so that while the fresh-water sponge (Spongilla) has but few and simple siliceous spicules, the Lithistidae are quite hard and strong. In most cases the inorganic skeleton is spicular, and not continuous; but in some, as " Venus's Flower Basket'1 (Euple3tella), a deli- cate fram
. Comparative anatomy and physiology. Chap. SPICULES OF SPONGES. 279 sponges), or the organic substance becomes impregnated with calcareous salts (calcareous sponges), or with siliceous (siliceous sponges). Considerable variations are, moreover, to be seen in the extent to which this impregnation takes place, so that while the fresh-water sponge (Spongilla) has but few and simple siliceous spicules, the Lithistidae are quite hard and strong. In most cases the inorganic skeleton is spicular, and not continuous; but in some, as " Venus's Flower Basket'1 (Euple3tella), a deli- cate framework of siliceous particles is left after all the or- ganic material has been removed (Fig. 114). The spicules vary considerably in form, being uniaxial or needle - shaped, tri- axial (this is the cha- racteristic form in the Calcispongise), or quadriaxial; connected with these are bi, tri, quadri, and sex- radiate spicules, which may by the loss of some, and the greater development of other rays, take on the most different shapes. Some spicules are multi-radiate, and others curved. Some project beyond the body of the sponge, as in the glass-rope sponge (Hyalonema; Fig. 115), where anchoring spicules as much as eighteen inches long have been observed. In addi- tion to these proper skeletal spicules, others which are smaller take an* important part in giving firmness to the sponge body, and even, as in the case of the. Fig. 114.—Section through the Wall of Euplectella (x 75). p, Pores; ?/, flagellated chambers. (After Schultze.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bell, F. J. (Francis Jeffrey), 1855-1924. London, Cassell
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