SPONGE WEAVERS. 117 



the catalogue of " Geniculated expando-ternate," 

 " Unipocillated bihamate," " Tridentate equi-ancho- 

 rate," or " Floricomo-hexradiate " spicules. Let it 

 suffice, to indicate their great variety of form, referring 

 to some figures in illustration (Plate III). Some of 

 these forms occur chiefly in the principal skeleton, 

 whilst others are confined to special parts, and have 

 their own special function, chiefly of strengthening 

 and supporting the sponge structure. It is noteworthy 

 that these spicules being of flint, and the most inde- 

 structible portion of the sponge, are often found in 

 most unexpected places, like the bones of a skeleton, 

 when no other portion of the sponge is to be seen. 

 They may be washed out from chalk, where they 

 have lain buried for thousands of years, and even 

 seen imbedded in a thin chipping of flint stone. The 

 microscope has detected them mixed with sand, or 

 associated with diatoms, in deposits laid down many 

 generations ago, in the stomachs of molluscs, fishes, 

 and even of marine birds of the present day ; in 

 fact, attached to almost everything that comes out 

 of the sea, and in nearly every spot over which the 

 ocean waters have ever flowed. It must not be for- 

 gotten that we allude in these remarks to the flinty 

 spicules of the siliceous sponges, which are by far 

 the most numerous, and not to the chalky or lime 

 spicules of the calcareous sponges, which are not in- 

 destructible ; the horny or kcratose sponges being 



