1825.] Mr. Gray on the Chemical Composition of Sponges. 431 



Article V. 



On the Chemical Composition oj Sponges. By John Edward 



Gray, Esq. MGS. 



(To the Editors of the Annals of Philosophy .) 



GENTLEMEN, British Museum. 



In my paper on Sponges in the ZoologicalJournal, I observed 

 that the sponges " all appear to be essentially formed after the 

 same manner, that is to say, of longitudinally placed transparent 

 fusiform spicule," and further, that " the fibres are composed of 

 spiculsB united by a cartilaginous substance." I collected a 

 quantityofspiculse, by washing them from a sponge in which they 

 were very large and distinct. I accidentally found that they 

 scratched glass, when rubbed hard against it. My attention 

 having been attracted to this fact, having before considered 

 them as mostly composed of carbonate or phosphate of lime, I 

 applied to my friend Mr. Children, stating the circumstance, 

 when he informed me that he had just observed that a sponge- 

 like body lately given to him by Mr. Heuland, which 

 proved to be a Tetht/a (a genus, which, in the before referred to 

 paper, 1 stated to be formed almost entirely of spiculae), consisted 

 wholly oipure silica, and a little animal matter. On subjecting 

 some sponges to experiment, considerable quantities of sihca 

 were found in the ashes o( Spongillafuviatitis, Spongia tomentosa, 

 and two or three other allied species ; and a small quantity in 

 Spongia officinalis, and a distinct trace, sufficient to form a glo- 

 bule before the blowpipe, in the ashes of a piece of the axis of 

 Gorgonia Flabellnm. 



The quantity cf silica appears, as might be expected, to be in 

 proportion to the density of the fibres of the sponge. 



Shortly afterwards, on looking over Ellis's Zoophiles, p. 178, 

 I found that he, in his description of Gorgonia Briareus (which 

 is now considered to be an anomalous species), states, that its 

 hard part (axis) or bone is composed of beautiful purple glassy 

 spiculae lying lengthways almost parallel to each other." 



After considerable search I have not been able to get or even 

 see a specimen of this interesting species, but there can be very 

 little doubt but that these spicule are also sihceous. 



This fact is exceedingly interesting in several points of view; 

 first, because silica is very rarely found as a product of the ani- 

 mal kingdom, and has never hitherto, that I am aware of, been 

 said to be found in the zoophytes, but only spoken of as a con- 

 stituent of hair and horn, to which the axis of the sponges and 

 gorgoniai have some resemblance ; secondly, as proving a consi- 

 derable affinity or resemblance in chemical composition, as well 

 as in external structure, to exist between the sea and freshwater 



